2011 Vol. 29, No. 4
Display Method:
2011, 29(4): 613-621.
Abstract:
Jijihu modern subaqueous aggradational fan (SAF) in Jungar Basin, Xinjiang Province, China, is 24m arch length and 10m radii. Jijihu SAF consists of alluvial fan 1, unit A (SAF), unit B (slop beds, retrogradational beds and flooding mudsand beds), unit C (alluvial fan 2) and unit D (alluvial fan 3) , which have been documented by Li by observing and digging during one week in the condition of 40 degree centigrade Junggar Basin after desert flood in 2007 summery time.
Field observation directs as followings: (1) Exception of alluvial fan 1, Jijihu SAF has the similar stacking patterns with East Coulee Delta (Posamentier et al., 1992). Especially, there is a 1cm red mud bed between alluvial fan 1 and SAF, directing that they belong to continuous sedimentation documented by digging. Although SAF covers alluvial fan 1 in the Northern side of pool, another isochronous unit opposite Jijihu SAF about 10m away in the Southern side directs the lowest alluvial fan clearly. Thereby, alluvial fan 1 becomes the lowest unit that may be interpreted as falling stage systems tract (FSST) during forced regression associated with incision, showing that pond water reaches lowest level. (2) Subsequently, pond level begins to rise, sediments supply exceeds the rate of level rise, and SAF (unit A) develops during normal regression, so that SAF may be interpreted as lowstand systems tract (LST) according to present scenario of sequence stratigraphy. (3) Associated with level rise exceeds sediments supply, unit B develops as follows: Firstly, fine mudsands begin to accumulate in front of SAF forming slope beds (i.e., healing phase wedge of Posamentiaer and Allen (1993)). Secondly, coarse sediments such as gravels deposits on the top of SAF, directing retrogression stacking patterns landward. Finely, level reaches to maximum, flooding mudsand beds begin to precipitate under hot wind in the Junggar Desert. Therefore, three parts (unit B) above may record as transgressive systems tract (TST) during transgression. (4) The second desert flood forms alluvial fan 2 (unit C) and 3 (unit D) incising one by one, they may be interpreted as falling stage systems tract (FSST) of another sequence during forced regression.
This article has compared the sequence stratigraphic significance between East Coulee Delta in Alberta and Jijihu subaqueous aggradational fan (SAF), and concluded as follows: (1) East Coulee Delta develops LSTTST superposition and FSST superposition that belong to two different depositional sequences; (2) Jijihu SAF develops FSSTLSTTST superposition and FSST superpositions that are attributed to two depositional sequences, too; (3) two outcrops has proved that no highstand systems tract develops after maximum flooding surface in modern smallscale pond, it is possible to represent difference between marine and nonmarine settings due to transporting energy in nonmarine setting not enough to carry sediments into pond. This paper has also discussed some key problems such as sequence boundary that is redefined as remnant maximum flooding surface (RMFS) and its correlative subaerial unconformity (CSU). Furthermore, this paper suggests avoidance of highstand normal regression term. In subsequent thesis authors will suggest that stillstand normal regression replace highstand normal regression.
Jijihu modern subaqueous aggradational fan (SAF) in Jungar Basin, Xinjiang Province, China, is 24m arch length and 10m radii. Jijihu SAF consists of alluvial fan 1, unit A (SAF), unit B (slop beds, retrogradational beds and flooding mudsand beds), unit C (alluvial fan 2) and unit D (alluvial fan 3) , which have been documented by Li by observing and digging during one week in the condition of 40 degree centigrade Junggar Basin after desert flood in 2007 summery time.
Field observation directs as followings: (1) Exception of alluvial fan 1, Jijihu SAF has the similar stacking patterns with East Coulee Delta (Posamentier et al., 1992). Especially, there is a 1cm red mud bed between alluvial fan 1 and SAF, directing that they belong to continuous sedimentation documented by digging. Although SAF covers alluvial fan 1 in the Northern side of pool, another isochronous unit opposite Jijihu SAF about 10m away in the Southern side directs the lowest alluvial fan clearly. Thereby, alluvial fan 1 becomes the lowest unit that may be interpreted as falling stage systems tract (FSST) during forced regression associated with incision, showing that pond water reaches lowest level. (2) Subsequently, pond level begins to rise, sediments supply exceeds the rate of level rise, and SAF (unit A) develops during normal regression, so that SAF may be interpreted as lowstand systems tract (LST) according to present scenario of sequence stratigraphy. (3) Associated with level rise exceeds sediments supply, unit B develops as follows: Firstly, fine mudsands begin to accumulate in front of SAF forming slope beds (i.e., healing phase wedge of Posamentiaer and Allen (1993)). Secondly, coarse sediments such as gravels deposits on the top of SAF, directing retrogression stacking patterns landward. Finely, level reaches to maximum, flooding mudsand beds begin to precipitate under hot wind in the Junggar Desert. Therefore, three parts (unit B) above may record as transgressive systems tract (TST) during transgression. (4) The second desert flood forms alluvial fan 2 (unit C) and 3 (unit D) incising one by one, they may be interpreted as falling stage systems tract (FSST) of another sequence during forced regression.
This article has compared the sequence stratigraphic significance between East Coulee Delta in Alberta and Jijihu subaqueous aggradational fan (SAF), and concluded as follows: (1) East Coulee Delta develops LSTTST superposition and FSST superposition that belong to two different depositional sequences; (2) Jijihu SAF develops FSSTLSTTST superposition and FSST superpositions that are attributed to two depositional sequences, too; (3) two outcrops has proved that no highstand systems tract develops after maximum flooding surface in modern smallscale pond, it is possible to represent difference between marine and nonmarine settings due to transporting energy in nonmarine setting not enough to carry sediments into pond. This paper has also discussed some key problems such as sequence boundary that is redefined as remnant maximum flooding surface (RMFS) and its correlative subaerial unconformity (CSU). Furthermore, this paper suggests avoidance of highstand normal regression term. In subsequent thesis authors will suggest that stillstand normal regression replace highstand normal regression.
2011, 29(4): 631-643.
Abstract:
Studies of the corresponding seismic data revealed the division plane is a sequence boundary (SB) (T3x truncated by the boundary and along which J1z onlaps). So it can be dertermined by LUNA principle. LUNA regards sequence boundary unconformity as can be recognized by strata geometry of abrupt change of accomodation generation rate which is marked by the paleochannel scale and the superimposition of channel sandstones, and base of the almagmated sandstone body is just the situ of the sequence boundary. In welllog, SB is presented by break point of Gr and Rt curvesthe reverse rhythm of the underlain sequence turns into positive rhythm of the overlying sequence upwards at the point. This plane coincides well with the base of basal conglomerate. Measuring the transboundary short columns along the west edge of Huayingshan and coresection studies have revealed that apparent differences of paleontologypaleoecology and sedimentology exist in between T3x and J1z successions, which reflect the inreversibility of geological evolution. Paleontology: mostly fossil plants, plants are plentiful and wellpreserved in T3x6 black shale, and plant stems are considerably common in coarse sandstone of the same member. Fossils are rare in J1z, however, allochthonous small carbonized plant debris or occasionally coal "pebbles" are seen. Sedimentary and diagenetic feafures: most aspects are quite different beween T3x6 and J1z, except that siderite concretions occur in the interval from below to above the boundary by several meters. Lithologythe lowermiddle part of T3x6 is represented by thick graywhite median (coarse)fine sandstone with single bed thickness of several to decades meters, the upper part by interbeds of light gray, yellowish gray fine sandstone to siltstone and black shales; however J1z is characterized by intercalations of light gray, grayishgreen thin siltstone and red, stained mudstome at its lower part, the mudstone are grading into gray colour and sandstone are getting thicker at its upper part. Composition——the guartz content in lower J1z is higher than the sandstones of T3x6, but its chert and metamorphic rock debris are apparently lower than the later; Texture maturity——J1z siltstone is much worsesorted than the T3xv6 sandstone, the thin turbidites in J1z are not seen in T3x successions. Sedimentary sturcturesbiclaylayers, herringbone structure, abrupt facies change, lenticular and flaser bedding and thin interbedds are common in T3x but not seen in J1z. Siliceous cobblethe J1z basal cobble is a reliable boundary marker which is easily differentiated from the basal ones of T3x6; the storminduced conglomerate and "oxhorn coal" occur only in T3x; rootlets are common seen in J1zv and occassionaly presented in T3x. Sedimenfary facies: the abovemention differences between T3x and J1z are thought to be derived from original sedimentary environments, the authors attribute T3x to shallow sea and estuarine origin and J1z to lacustrine delta system. The two successions are also different from each other in welllogging responses and can be easily discerned. This paper proved that to judge the reached stratigraphic level during welldrilling swiftly on the basis of cutting information can be achieved.
Studies of the corresponding seismic data revealed the division plane is a sequence boundary (SB) (T3x truncated by the boundary and along which J1z onlaps). So it can be dertermined by LUNA principle. LUNA regards sequence boundary unconformity as can be recognized by strata geometry of abrupt change of accomodation generation rate which is marked by the paleochannel scale and the superimposition of channel sandstones, and base of the almagmated sandstone body is just the situ of the sequence boundary. In welllog, SB is presented by break point of Gr and Rt curvesthe reverse rhythm of the underlain sequence turns into positive rhythm of the overlying sequence upwards at the point. This plane coincides well with the base of basal conglomerate. Measuring the transboundary short columns along the west edge of Huayingshan and coresection studies have revealed that apparent differences of paleontologypaleoecology and sedimentology exist in between T3x and J1z successions, which reflect the inreversibility of geological evolution. Paleontology: mostly fossil plants, plants are plentiful and wellpreserved in T3x6 black shale, and plant stems are considerably common in coarse sandstone of the same member. Fossils are rare in J1z, however, allochthonous small carbonized plant debris or occasionally coal "pebbles" are seen. Sedimentary and diagenetic feafures: most aspects are quite different beween T3x6 and J1z, except that siderite concretions occur in the interval from below to above the boundary by several meters. Lithologythe lowermiddle part of T3x6 is represented by thick graywhite median (coarse)fine sandstone with single bed thickness of several to decades meters, the upper part by interbeds of light gray, yellowish gray fine sandstone to siltstone and black shales; however J1z is characterized by intercalations of light gray, grayishgreen thin siltstone and red, stained mudstome at its lower part, the mudstone are grading into gray colour and sandstone are getting thicker at its upper part. Composition——the guartz content in lower J1z is higher than the sandstones of T3x6, but its chert and metamorphic rock debris are apparently lower than the later; Texture maturity——J1z siltstone is much worsesorted than the T3xv6 sandstone, the thin turbidites in J1z are not seen in T3x successions. Sedimentary sturcturesbiclaylayers, herringbone structure, abrupt facies change, lenticular and flaser bedding and thin interbedds are common in T3x but not seen in J1z. Siliceous cobblethe J1z basal cobble is a reliable boundary marker which is easily differentiated from the basal ones of T3x6; the storminduced conglomerate and "oxhorn coal" occur only in T3x; rootlets are common seen in J1zv and occassionaly presented in T3x. Sedimenfary facies: the abovemention differences between T3x and J1z are thought to be derived from original sedimentary environments, the authors attribute T3x to shallow sea and estuarine origin and J1z to lacustrine delta system. The two successions are also different from each other in welllogging responses and can be easily discerned. This paper proved that to judge the reached stratigraphic level during welldrilling swiftly on the basis of cutting information can be achieved.
2011, 29(4): 658-664.
Abstract:
Mesoproterozoic folded basement was unexposed in central Guizhou province. The thickness and facies of the regional Neoproterozoic sedimentary cover and stratigraphic contact relationship reveal that the Central Guizhou palaeouplift was on the high position of the folded basement before Nanhuaian. South and north margins were still receiving deposits within relative low position of the basement. Neoproterozoic rifting history and geophysical proof also indicate that the basement might have some differences between the palaeouplift area and the marginal area. Thus, we could speculate that there has Mesoproterozoic folded basement under the sedimentary cover in correspondence with Sibao Group. Central Guizhou palaeouplift was lying on the high position of the folded basement. Compressive stress of southnorth direction of the folded basement determines the palaeouplift's distribution in the eastwest direction after uplifted above the seawater level. During the period of Sinian and Cambrian, the folded basement of the palaeouplift was under the sedimentary strata. The strata in this area are continuous deposits with a relatively stable structure. Honghuayuan Formation's offlap and Meitan Formation's overlap shows that the folded basement and sedimentary strata above were uplifted and became a palaeouplift at the beginning of Ordovician. Periphery area, however, was still receiving deposits. The palaeouplift's obvious uplift by the influence of Duyun Movement between the Ordovician and Silurian had made the periphery area exposure, resulting in karst and offlapoverlap of the strata. Within the process of uplift, the sedimentary system of the south and north margins was separated with certain degrees. In MidLate Silurian, the last episode of Caledonian Movement occurred strongly. During this movement period, seawater regressed from the Middle and Upper Yangtze block, and the Central Guizhou Palaeouplift became one part of the land. Duyun Movement had great impact on this palaeouplift, but the effect of basement forms and structural trend was its forming mechanism.
Mesoproterozoic folded basement was unexposed in central Guizhou province. The thickness and facies of the regional Neoproterozoic sedimentary cover and stratigraphic contact relationship reveal that the Central Guizhou palaeouplift was on the high position of the folded basement before Nanhuaian. South and north margins were still receiving deposits within relative low position of the basement. Neoproterozoic rifting history and geophysical proof also indicate that the basement might have some differences between the palaeouplift area and the marginal area. Thus, we could speculate that there has Mesoproterozoic folded basement under the sedimentary cover in correspondence with Sibao Group. Central Guizhou palaeouplift was lying on the high position of the folded basement. Compressive stress of southnorth direction of the folded basement determines the palaeouplift's distribution in the eastwest direction after uplifted above the seawater level. During the period of Sinian and Cambrian, the folded basement of the palaeouplift was under the sedimentary strata. The strata in this area are continuous deposits with a relatively stable structure. Honghuayuan Formation's offlap and Meitan Formation's overlap shows that the folded basement and sedimentary strata above were uplifted and became a palaeouplift at the beginning of Ordovician. Periphery area, however, was still receiving deposits. The palaeouplift's obvious uplift by the influence of Duyun Movement between the Ordovician and Silurian had made the periphery area exposure, resulting in karst and offlapoverlap of the strata. Within the process of uplift, the sedimentary system of the south and north margins was separated with certain degrees. In MidLate Silurian, the last episode of Caledonian Movement occurred strongly. During this movement period, seawater regressed from the Middle and Upper Yangtze block, and the Central Guizhou Palaeouplift became one part of the land. Duyun Movement had great impact on this palaeouplift, but the effect of basement forms and structural trend was its forming mechanism.
2011, 29(4): 677-688.
Abstract:
As an important sedimentary phenomenon, gravity flow sedimentation is widespread in deepmarine and deeplacustrine environments. Obviously, differentiation of different types of gravityflow sediments is crucial for reconstructing paleodepositional environment. Four distinct types of gravity flows and their diagnostic sedimentary structures are introduced, which can be used as guide for field identification. Debris flow depositions are characterized of their disorganized internal texture, flat bed base, and parallelism of planar clasts to bedding. Thickbedded and massive sandstones are usually formed by hyperconcentrated density flow; typified by occurrence of outsized clasts, ripup mudstones, water escape structures and other liquefactionrelated structures. Grain flow is a subtype of hyperconcentrated density flows, and inverse grading is characteristic of its deposits. Concentrated density flow possesses the depositional characteristics of both hyperconcentrated density flow and turbidity current. Tad divisions in Bouma sequence are the products of one turbidity current event, but only Ta is formed from turbidity current. Tbc divisions are actually generated from traction flow, whereas Td division is fallout deposits. Flow transformation can occur in the processes of gravity flows, and the gravityflow sediments are often reworked by bottom currents and bypass flows to varying degrees.
As an important sedimentary phenomenon, gravity flow sedimentation is widespread in deepmarine and deeplacustrine environments. Obviously, differentiation of different types of gravityflow sediments is crucial for reconstructing paleodepositional environment. Four distinct types of gravity flows and their diagnostic sedimentary structures are introduced, which can be used as guide for field identification. Debris flow depositions are characterized of their disorganized internal texture, flat bed base, and parallelism of planar clasts to bedding. Thickbedded and massive sandstones are usually formed by hyperconcentrated density flow; typified by occurrence of outsized clasts, ripup mudstones, water escape structures and other liquefactionrelated structures. Grain flow is a subtype of hyperconcentrated density flows, and inverse grading is characteristic of its deposits. Concentrated density flow possesses the depositional characteristics of both hyperconcentrated density flow and turbidity current. Tad divisions in Bouma sequence are the products of one turbidity current event, but only Ta is formed from turbidity current. Tbc divisions are actually generated from traction flow, whereas Td division is fallout deposits. Flow transformation can occur in the processes of gravity flows, and the gravityflow sediments are often reworked by bottom currents and bypass flows to varying degrees.
2011, 29(4): 695-703.
Abstract:
Slope channel complex is one of the most important sedimentary architecture elements in Pliocene in Rakhine Basin, offshore Myanmar. This study is carried out under the guidance of the relationship between the seismic response and deepwater reservoir. The strong amplitude attributes on 2D and 3D seismic data are applied to deduce coarse sediment existing in slope channel complexes. Technologies that include coherence slice analysis, geoanomaly processing and 3D visualization are used for distinguishing slope channel complexes from background. Detailed descriptions, involving the external geometric shape, the nature of internal fill and reservoir characters are executed.
Three kinds of slope channel complexes have been observed and identified based on the 3D seismic data. Multiple phase aggradational confined channel complexes have been detected in Pliocene in Rakhine Basin. Several large sand bodies, ranging from 7 km to 16 km in the downcurrent direction and usually no more than 10 km in width, have been indentified. These sands comprised 3~5 layers vertically and are related with each other.
Channel complexes analysis and characterization in this research area result in the recognitions that the confined channel complexes with complicated shapes and sustainable change on morphology and packing characteristics downstream in lower Pliocene are developed. The confined channel complexes in Pliocene can be characterized by three major categories of erosional confined channel complexes, erosional/external aggradational confined channel complexes and aggradational confined channel complexes according to the difference of sedimentary fill. This study reveals that aggradational channel complexes are richer in reservoir than other two types. They are composite features made up of smaller various sandrich subenvironments, such as inside channels, frontal splays, crevasse splays and overbanks that can be identified by seismic anomaly process method. It is inferred that some sands with larger thickness and high vertical continuity probably exit in aggradational confined channel complexes according to the data measured by previous researchers. It is hoped to become Highrate, highultimaterecovery reservoirs and be considered as the most beneficial targets in the Rakhine Basin.
Slope channel complex is one of the most important sedimentary architecture elements in Pliocene in Rakhine Basin, offshore Myanmar. This study is carried out under the guidance of the relationship between the seismic response and deepwater reservoir. The strong amplitude attributes on 2D and 3D seismic data are applied to deduce coarse sediment existing in slope channel complexes. Technologies that include coherence slice analysis, geoanomaly processing and 3D visualization are used for distinguishing slope channel complexes from background. Detailed descriptions, involving the external geometric shape, the nature of internal fill and reservoir characters are executed.
Three kinds of slope channel complexes have been observed and identified based on the 3D seismic data. Multiple phase aggradational confined channel complexes have been detected in Pliocene in Rakhine Basin. Several large sand bodies, ranging from 7 km to 16 km in the downcurrent direction and usually no more than 10 km in width, have been indentified. These sands comprised 3~5 layers vertically and are related with each other.
Channel complexes analysis and characterization in this research area result in the recognitions that the confined channel complexes with complicated shapes and sustainable change on morphology and packing characteristics downstream in lower Pliocene are developed. The confined channel complexes in Pliocene can be characterized by three major categories of erosional confined channel complexes, erosional/external aggradational confined channel complexes and aggradational confined channel complexes according to the difference of sedimentary fill. This study reveals that aggradational channel complexes are richer in reservoir than other two types. They are composite features made up of smaller various sandrich subenvironments, such as inside channels, frontal splays, crevasse splays and overbanks that can be identified by seismic anomaly process method. It is inferred that some sands with larger thickness and high vertical continuity probably exit in aggradational confined channel complexes according to the data measured by previous researchers. It is hoped to become Highrate, highultimaterecovery reservoirs and be considered as the most beneficial targets in the Rakhine Basin.
2011, 29(4): 712-723.
Abstract:
The lower part of Xingouzui Formation of Mawangmiao area is an important producing pay and profitable range to find lithologic hydrocarbon reservoir in the future. Based on the synthetical analysis of cores description, thin section analysis and logs, and combined with sedimentary marks of lithology, paleoclimate, sedimentary structure, and so on,
the lower segment of Xingouzui Formation is ascertained shallow water deltashoreshallow lacus depositional system, and is further divided into subfacies as follows: delta front, prodelta, shoreshallow lacus, etc. and several microfacies. Provenance analysis results indicate that the study area is controlled by northeastern Hanchuan provenance and northwestern Hanshui provenance, the study area develops two lobate deltas of NESW and NWES distribution, especially the NESW delta develop more widely. During the Ⅱoil group depositional stage, depositional water depth is the most deep, and the delta develop most widely, Ⅲoil group takes second place. And during the Ⅰoil group depositional stage, depositional water depth is the most shallow and the delta develop most shallowly. Most of all, the underwater distributary channel microfacies develop most widely. Through analyzing sedimentary facies distribution and reservoir sands distributing rule of three oil groups and important sections of Xia31,Xia25 and Xia13, indicate that the underwater distributary channel microfacies of Xia25 has most wide scale and most thick sand, the sand distribution rule according to underwater distributary channel distribution. The sedimentary facies distribution of Xia31 and Xia13 coincide with the Xia25 and northwestern delta front sand of Xia31 develop more wide. The result of analyzing every microfacies reservoir physical property indicates that underwater distributary channel has highest porosity. Thus underwater distributary channel microfacies and thicker sand distribution region of each section should be optimum reservoir facies and beneficial region to seek for lithologic hydrocarbon reservoirs.
The lower part of Xingouzui Formation of Mawangmiao area is an important producing pay and profitable range to find lithologic hydrocarbon reservoir in the future. Based on the synthetical analysis of cores description, thin section analysis and logs, and combined with sedimentary marks of lithology, paleoclimate, sedimentary structure, and so on,
the lower segment of Xingouzui Formation is ascertained shallow water deltashoreshallow lacus depositional system, and is further divided into subfacies as follows: delta front, prodelta, shoreshallow lacus, etc. and several microfacies. Provenance analysis results indicate that the study area is controlled by northeastern Hanchuan provenance and northwestern Hanshui provenance, the study area develops two lobate deltas of NESW and NWES distribution, especially the NESW delta develop more widely. During the Ⅱoil group depositional stage, depositional water depth is the most deep, and the delta develop most widely, Ⅲoil group takes second place. And during the Ⅰoil group depositional stage, depositional water depth is the most shallow and the delta develop most shallowly. Most of all, the underwater distributary channel microfacies develop most widely. Through analyzing sedimentary facies distribution and reservoir sands distributing rule of three oil groups and important sections of Xia31,Xia25 and Xia13, indicate that the underwater distributary channel microfacies of Xia25 has most wide scale and most thick sand, the sand distribution rule according to underwater distributary channel distribution. The sedimentary facies distribution of Xia31 and Xia13 coincide with the Xia25 and northwestern delta front sand of Xia31 develop more wide. The result of analyzing every microfacies reservoir physical property indicates that underwater distributary channel has highest porosity. Thus underwater distributary channel microfacies and thicker sand distribution region of each section should be optimum reservoir facies and beneficial region to seek for lithologic hydrocarbon reservoirs.
2011, 29(4): 734-743.
Abstract:
As the world's deep water oil and gas exploration continue to strengthen, the deepwater basin has increasingly become the new areas to gain growth in oil and gas reserves. The deepsea oil and gas exploration has developed the inevitable challenges. Therefore, to make related research about the deep exploration and development in particular characteristic of the reservoir is a necessary requirement to find deep water oil and gas and also the direction of ocean exploration. Pearl River Mouth Basin is a major basin in China's offshore oil and gas basins with low level of exploration and the lacking comprehensive research on the variation law and influencing factors of reservoir properties. Deep reservoir with high porosity has been increasingly developed the concern problem with oil exploration performing to deep zone by petroleum geologists. The formation mechanism and controlling factors of the secondary porosity are reasonably explained or not, which directly impacts on the establishment of oil and gas basin clastic reservoir quality prediction model and serious impact on the objective evaluation of the reservoir. In this paper, the constraints of the factors of the secondary porosity in the study area are discussed systemically by isotope geochemistry, organic geochemistry methods combined with sedimentology. The study area contains a large number of grains and grain dissolution pore, according to sandstone sheet, cast thin sections, scanning electron microscopy analysis. Based on reservoir property data, two secondary porosity zones can be found in the Tertiary reservoirs, Baiyun Sag, mainly in the 2 750～3 800 m and 3 500～4 600 m. Mineral grains and carbonate cement are dissolved forming large of intergranular dissolution pores and dissolution pores. By isotope tracing method, it is found that the formation of secondary porosity is caused by the organic acid. Organic maturity and acidic water in which CO2 is released by decarboxylation of organic matter in the process of diagenesis were the main reason. The feldspar particles, containing feldspar volcanic debris, early carbonate cements and fossils in the reservoir are dissolved by organic acid. The distribution of oxygen and carbon isotope of clastic rocks in the study area is that the value of δ13C changes in between 11.8 ‰ and 3.4 ‰ and δ18O value changes in between 17.8 ‰ and 2.4 ‰. If 13C in carbonate cements is only from the depositional pore water, δ13C value can not be so low. So, organic acids from kerogen decarboxylation must join in the process of the formation carbonate cements in the deep burial. Affecting the secondary porosity of the geological factors include the distribution and types of hydrocarbon source rocks, sandbodies distribution in the sedimentary facies and sandstone types, fracture resulting from tectonic activity. In Pearl River Mouth Basin, there are 4 sets of hydrocarbon source rocks including the Eocene Wenchang Formation, the Eocene oligocene Enping Formation, upperthe Oligocene Zhuhai Formation and under the Miocene Zhujiang Formation. As the types of organic matter are mainly Ⅰand Ⅱin these 4 sets of hydrocarbon source rocks, the research area's hydrocarbon source rocks are suitable to produce the acid and have strong ability to produce the sour fluid. Wenchang source rocks in which the value of Ro is up to 3.0% has been in mature or even over mature. Enping source rocks has dnter the mature stage, Ro=1.0% to 1.5%. The Ro value of Zhuhai source rocks is 0.43% ~ 0.53%. The main hydrocarbon source rocks enter the stage of producing sour fluid, which can provide the massive acidic fluid for dissolving the oil gas reservoir. The reservoir clastic rocks are main the silicarenite and the debris silicarenite which have the high constitute and structure maturity. Therefore, it is advantageous that the organic acid enters the reservoir to form the secondary pores. The development of faults and sandstone layer which act as the bridge between source rocks and reservoir to make a steady stream of organic acids migrating from the lower strata to shallow reservoirs in the Panyu lower uplift Baiyun Sag North Slope. In addition, secondary porosity is also controlled by the matching hydrocarbon source rock maturity time with migration pathway system which includes faults, sand body and ancient structural ridge. When the organic acids migrate into the study area, there are the active faults and sands which can provide the longdistance lateral migration of oil and gas. Formation of secondary porosity is a systematically geological processes. Its formation and preservation are relevant to many aspects such as basin heat flow, tectonic evolution, sedimentation, diagenesis, fluid nature, and fluid migration and so on. After comprehensively analyzing various geological factors, the model which describes the organic acids forming secondary porosity can be summed up as "production, transportation, matching, and dissolution." Only the geological factors matching with each other can the secondary porosity be produced. These cognitions have good guidance for predicting highquality reservoir in the studied area.
As the world's deep water oil and gas exploration continue to strengthen, the deepwater basin has increasingly become the new areas to gain growth in oil and gas reserves. The deepsea oil and gas exploration has developed the inevitable challenges. Therefore, to make related research about the deep exploration and development in particular characteristic of the reservoir is a necessary requirement to find deep water oil and gas and also the direction of ocean exploration. Pearl River Mouth Basin is a major basin in China's offshore oil and gas basins with low level of exploration and the lacking comprehensive research on the variation law and influencing factors of reservoir properties. Deep reservoir with high porosity has been increasingly developed the concern problem with oil exploration performing to deep zone by petroleum geologists. The formation mechanism and controlling factors of the secondary porosity are reasonably explained or not, which directly impacts on the establishment of oil and gas basin clastic reservoir quality prediction model and serious impact on the objective evaluation of the reservoir. In this paper, the constraints of the factors of the secondary porosity in the study area are discussed systemically by isotope geochemistry, organic geochemistry methods combined with sedimentology. The study area contains a large number of grains and grain dissolution pore, according to sandstone sheet, cast thin sections, scanning electron microscopy analysis. Based on reservoir property data, two secondary porosity zones can be found in the Tertiary reservoirs, Baiyun Sag, mainly in the 2 750～3 800 m and 3 500～4 600 m. Mineral grains and carbonate cement are dissolved forming large of intergranular dissolution pores and dissolution pores. By isotope tracing method, it is found that the formation of secondary porosity is caused by the organic acid. Organic maturity and acidic water in which CO2 is released by decarboxylation of organic matter in the process of diagenesis were the main reason. The feldspar particles, containing feldspar volcanic debris, early carbonate cements and fossils in the reservoir are dissolved by organic acid. The distribution of oxygen and carbon isotope of clastic rocks in the study area is that the value of δ13C changes in between 11.8 ‰ and 3.4 ‰ and δ18O value changes in between 17.8 ‰ and 2.4 ‰. If 13C in carbonate cements is only from the depositional pore water, δ13C value can not be so low. So, organic acids from kerogen decarboxylation must join in the process of the formation carbonate cements in the deep burial. Affecting the secondary porosity of the geological factors include the distribution and types of hydrocarbon source rocks, sandbodies distribution in the sedimentary facies and sandstone types, fracture resulting from tectonic activity. In Pearl River Mouth Basin, there are 4 sets of hydrocarbon source rocks including the Eocene Wenchang Formation, the Eocene oligocene Enping Formation, upperthe Oligocene Zhuhai Formation and under the Miocene Zhujiang Formation. As the types of organic matter are mainly Ⅰand Ⅱin these 4 sets of hydrocarbon source rocks, the research area's hydrocarbon source rocks are suitable to produce the acid and have strong ability to produce the sour fluid. Wenchang source rocks in which the value of Ro is up to 3.0% has been in mature or even over mature. Enping source rocks has dnter the mature stage, Ro=1.0% to 1.5%. The Ro value of Zhuhai source rocks is 0.43% ~ 0.53%. The main hydrocarbon source rocks enter the stage of producing sour fluid, which can provide the massive acidic fluid for dissolving the oil gas reservoir. The reservoir clastic rocks are main the silicarenite and the debris silicarenite which have the high constitute and structure maturity. Therefore, it is advantageous that the organic acid enters the reservoir to form the secondary pores. The development of faults and sandstone layer which act as the bridge between source rocks and reservoir to make a steady stream of organic acids migrating from the lower strata to shallow reservoirs in the Panyu lower uplift Baiyun Sag North Slope. In addition, secondary porosity is also controlled by the matching hydrocarbon source rock maturity time with migration pathway system which includes faults, sand body and ancient structural ridge. When the organic acids migrate into the study area, there are the active faults and sands which can provide the longdistance lateral migration of oil and gas. Formation of secondary porosity is a systematically geological processes. Its formation and preservation are relevant to many aspects such as basin heat flow, tectonic evolution, sedimentation, diagenesis, fluid nature, and fluid migration and so on. After comprehensively analyzing various geological factors, the model which describes the organic acids forming secondary porosity can be summed up as "production, transportation, matching, and dissolution." Only the geological factors matching with each other can the secondary porosity be produced. These cognitions have good guidance for predicting highquality reservoir in the studied area.
2011, 29(4): 752-760.
Abstract:
he Shamuluo Formation of Upper Jurassic in Dongqiao is mainly composed of a series of tidal flat and carbonate platform deposits and especially characterized by a lot of organic reefs. Reefbuilding organisms are chiefly Stromatoproids, and secondly hexacorals. Among Stromatoporoids, there are different forms such as dendritic, cylindric and massive,which reflects the second prosperous period since the late Devonian recession during geological history. The reefbuilding organisms mentioned above are the majority preservated at the original growth state, which all require warm, clean and normal shallow water environment with abundant light and better circulation. Through the study of individual ecology and analysis on the assemblage of reefbuilding organisms, three reefbuilding communities are recognized, namely MilleporidiumCladocoropsis, CladocoropsisMilleporidiumMilleporella and MilleporidiumActinatraea community.
〓〓The analysis of sealevel changes indicate that it exists three sealevel change cycles of the reefbearing strata in the study areas, among them, the first cycles developed in the lower section of the Shamuluo Formation, namely clastic rocks Member; whereas the second cycle developed in the lower part of the second Member of Shamuluo Formation and sealevel rising caused reefbuilding organisms prosperous breeding such as stromatoproids to form the first prosperous period since the late Devonian recession and shaped the first buildingreefs community, namely MilleporidiumCladocoropsis community; the third sealevel change occurs in the upper part of the second Member of Shamuluo Formation and shaped the secondthirdterm reefs resulting the development of the Cladocoropsis—Milleporidium—Milleporella community and Milleporidium—Actinatraea community. Replacement is the only form to the evolution of community，which is duo to the unstable of relative sealevel changes during the sealevel change peroid. It is due to the existing of the several subordinate cycles during the sealevel change peroid that the reefs are characterized by discontinuous and little thickness.The decline of reefs in the area is mostly due to slow rising of sealevel, resulting in the growth rate of accommodation was slower than the sediment accumulation, and showing by mostly sparry calcarenite of he reefcovers.
〓〓The authors hold that the existence of reef communities is of great significance for further studying BangongcuoNujiang suture zone merging time. They consider that oceanic crust subduction time of middle BangongcuoNujiang River suture zone(i.e. Dongqiao region of Anduo) should be in the late Jurassic or before the deposition of Shamuluo Formation of Late Jurassic (Shamuluo Formation is unconformably on the Late Jurassic hyperbasite) and after ultramafic rock Formation of the Late Jurassic. Because of the subduction, the study area was uplift as land and formed angular unconformity between Shamuluo Formation and the underlying Late Jurassic ultramafic rock. The existence of reef communities of Late Jurassic Shamuluo Formation showed that the study area may belong to a part of shallow continental shelf of the remaining backarc basin after BangongcuoNujiang River oceanic crust subduction.
he Shamuluo Formation of Upper Jurassic in Dongqiao is mainly composed of a series of tidal flat and carbonate platform deposits and especially characterized by a lot of organic reefs. Reefbuilding organisms are chiefly Stromatoproids, and secondly hexacorals. Among Stromatoporoids, there are different forms such as dendritic, cylindric and massive,which reflects the second prosperous period since the late Devonian recession during geological history. The reefbuilding organisms mentioned above are the majority preservated at the original growth state, which all require warm, clean and normal shallow water environment with abundant light and better circulation. Through the study of individual ecology and analysis on the assemblage of reefbuilding organisms, three reefbuilding communities are recognized, namely MilleporidiumCladocoropsis, CladocoropsisMilleporidiumMilleporella and MilleporidiumActinatraea community.
〓〓The analysis of sealevel changes indicate that it exists three sealevel change cycles of the reefbearing strata in the study areas, among them, the first cycles developed in the lower section of the Shamuluo Formation, namely clastic rocks Member; whereas the second cycle developed in the lower part of the second Member of Shamuluo Formation and sealevel rising caused reefbuilding organisms prosperous breeding such as stromatoproids to form the first prosperous period since the late Devonian recession and shaped the first buildingreefs community, namely MilleporidiumCladocoropsis community; the third sealevel change occurs in the upper part of the second Member of Shamuluo Formation and shaped the secondthirdterm reefs resulting the development of the Cladocoropsis—Milleporidium—Milleporella community and Milleporidium—Actinatraea community. Replacement is the only form to the evolution of community，which is duo to the unstable of relative sealevel changes during the sealevel change peroid. It is due to the existing of the several subordinate cycles during the sealevel change peroid that the reefs are characterized by discontinuous and little thickness.The decline of reefs in the area is mostly due to slow rising of sealevel, resulting in the growth rate of accommodation was slower than the sediment accumulation, and showing by mostly sparry calcarenite of he reefcovers.
〓〓The authors hold that the existence of reef communities is of great significance for further studying BangongcuoNujiang suture zone merging time. They consider that oceanic crust subduction time of middle BangongcuoNujiang River suture zone(i.e. Dongqiao region of Anduo) should be in the late Jurassic or before the deposition of Shamuluo Formation of Late Jurassic (Shamuluo Formation is unconformably on the Late Jurassic hyperbasite) and after ultramafic rock Formation of the Late Jurassic. Because of the subduction, the study area was uplift as land and formed angular unconformity between Shamuluo Formation and the underlying Late Jurassic ultramafic rock. The existence of reef communities of Late Jurassic Shamuluo Formation showed that the study area may belong to a part of shallow continental shelf of the remaining backarc basin after BangongcuoNujiang River oceanic crust subduction.
2011, 29(4): 761-766.
Abstract:
The settling particulate matter(SPM) was collected respectively by selfmade sediment trap in Jiulongjiang estuary from March 28 to March 29 in 2009. The collected samples were analyzed using scanning electron microscope (SEM), laser particle size analyzer and ICPMS instrument, and the particulate vertical fluxes were caculated. SEM analysis using the LEO1530 scanning electron microscope made in Philip company in nanometer technology centre of Xiamen University(resolution for the 3 nm, the largest magnification is 30 millions times). Grain size analysis was analyzed by Mastersizer 2000 type laser granulometer, samples were determined after ultrasonic dispersed, particle size interval for 0.25, precision is 2%, the work was done by open laboratory of ocean & coast environmental geology, third institute of oceanography. ICPMS analysis, element analysis are finished by using inductively coupled plasma mass spectrometer (Agilent 7500ce ICPMS, American Agilent) in key laboratory of global change and marineatmospheric chemistry,SOA. We have analyzed 47 elements, including Na, Mg, Al, K, Ca, Fe, V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Sn, Sb, Hg, Tl,Pb,Th,U, such elements (partly elements because of low content were not detected), the instrument measuring precision standard deviation is less than 5%. Using the scales measurement accuracy for 1/100000 to calculated vertical settlement particulate flux. SEM analysis shows that biological debris and minerals are the main components of settling particulate matter, the flocculation types are different in disparate levels. Every surface and bottom are silty sand, median diameter vary slightly. The change of size parameters were effected by flocculation. The vertical flux of settlement between sea level changes greatly. The surface of settlement flux are higher than the bottom in A and C station, B staion emerge to the contrary. Settlement flux peak in B station bottom, settlement flux for 747.0 g.m2.d1,lowest appeared in A station bottom, settlement flux for 245.7 g m2 d1, investigate its reason should be derived from Jiulongjiang of particulate yakees along the subsidence. There are certain differences in different sources of substance in the chemically, particle chemical composition is the comprehensive embodiment of the source. The content and distribution characteristic of each element in settlement particle is one of the important indexes of material sources, biogeochemical process, material exchange between particles and ecological environment of marine.In order to reveal the relationship between each element, the principal component analysis is carried on the factor analysis, former four factors have given a fully summary to the vast majority figures and explained 94.927% variance of the total. Factor1 reflects the effect of distribution of the particle caused by inputing of landsourced material. Factor 2 is also reflect the terrestrial material input on the distribution of the settlement of particles, and indicates that the trace elements of particle did not exists in the form of carbonate. Factor 3 reflects the effect of the distribution of the settlement particle by human activities in the study area .Factor 4 revals the same conclusion with factor 3.
The settling particulate matter(SPM) was collected respectively by selfmade sediment trap in Jiulongjiang estuary from March 28 to March 29 in 2009. The collected samples were analyzed using scanning electron microscope (SEM), laser particle size analyzer and ICPMS instrument, and the particulate vertical fluxes were caculated. SEM analysis using the LEO1530 scanning electron microscope made in Philip company in nanometer technology centre of Xiamen University(resolution for the 3 nm, the largest magnification is 30 millions times). Grain size analysis was analyzed by Mastersizer 2000 type laser granulometer, samples were determined after ultrasonic dispersed, particle size interval for 0.25, precision is 2%, the work was done by open laboratory of ocean & coast environmental geology, third institute of oceanography. ICPMS analysis, element analysis are finished by using inductively coupled plasma mass spectrometer (Agilent 7500ce ICPMS, American Agilent) in key laboratory of global change and marineatmospheric chemistry,SOA. We have analyzed 47 elements, including Na, Mg, Al, K, Ca, Fe, V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Sn, Sb, Hg, Tl,Pb,Th,U, such elements (partly elements because of low content were not detected), the instrument measuring precision standard deviation is less than 5%. Using the scales measurement accuracy for 1/100000 to calculated vertical settlement particulate flux. SEM analysis shows that biological debris and minerals are the main components of settling particulate matter, the flocculation types are different in disparate levels. Every surface and bottom are silty sand, median diameter vary slightly. The change of size parameters were effected by flocculation. The vertical flux of settlement between sea level changes greatly. The surface of settlement flux are higher than the bottom in A and C station, B staion emerge to the contrary. Settlement flux peak in B station bottom, settlement flux for 747.0 g.m2.d1,lowest appeared in A station bottom, settlement flux for 245.7 g m2 d1, investigate its reason should be derived from Jiulongjiang of particulate yakees along the subsidence. There are certain differences in different sources of substance in the chemically, particle chemical composition is the comprehensive embodiment of the source. The content and distribution characteristic of each element in settlement particle is one of the important indexes of material sources, biogeochemical process, material exchange between particles and ecological environment of marine.In order to reveal the relationship between each element, the principal component analysis is carried on the factor analysis, former four factors have given a fully summary to the vast majority figures and explained 94.927% variance of the total. Factor1 reflects the effect of distribution of the particle caused by inputing of landsourced material. Factor 2 is also reflect the terrestrial material input on the distribution of the settlement of particles, and indicates that the trace elements of particle did not exists in the form of carbonate. Factor 3 reflects the effect of the distribution of the settlement particle by human activities in the study area .Factor 4 revals the same conclusion with factor 3.
2011, 29(4): 776-782.
Abstract:
The Yellow River contains large amounts of sands, resulting in a peculiar hydraulic condition which is characterized by a magnificent interface between the particulates and water. In addition, Baotou section of the Yellow River suffers from severe heavy metal pollution receiving the industrial discharges from the Baotou city. Therefore, this study was carried out on Baotou section of the Yellow River based on its representativeness on the mechanism of heavy metal adsorption on watersediment interface, and on the heavy metal spatial distribution, mobilization, transformation, and accumulation effects in sediments. Because of their persistence in the environment, heavy metals often pose threats to aquatic lives and plants in the environment. Based on the theories and methods of environmental geochemistry, biogeochemistry, pollution ecology and modern sedimentology, the speciation distribution characters of heavy metals such as Cu, Pb, Zn in the different grain sizes sediments and the contribution of the different grain sizes sediments on the concentrations of different heavy metals speciation were discussed in this work. The results indicated that the bound to FeMn oxide was the dominant form of nonsteadystate of Cu, Pb, and Zn in different grain sizes sediments from the Yellow River, and there were the concentration order of the bound to FeMn oxide ＞ the bound to carbonate ＞ the bound to organic matter for Cu and Pb, while the bound to FeMn oxide ＞ the bound to organic matter ＞ the bound to carbonate for Zn. The grainsize effects of the different species for the selected heavy metals were observed in this work which was the results of particle size and active components such as organic matter, carbonate and FeMn oxides in different grain sizes sediments from the studied section of the Yellow River. In all of the factors, the particle sizes played a key role in affecting the concentration of different species of the selected heavy metals. Based on the experiments, it was found that the bound to FeMn oxides was the dominant form in different size fractions of sediments from Baotou Section of the Yellow River, and its concentration was mainly influenced by the content of Fe oxide in different grain sizes sediments from the studied section of the Yellow River. The results also showed that the concentrations of each species were ranked as Zn＞Pb＞Cu in the same size fraction sediments, which was not consistent with the background values of heavy metals in sediment from the midstream of the Yellow River. The differences found in this work indicated that there were exogenous heavy metals inputs from the industrial wastewater of the Baotou City from another point of view. The dominant forms of Cu, Pb and Zn are FeMn oxides bound and bound to organic matter in sediments from the tributaries of the Yellow River. From the comparison between the main stream and the tributaries of the Baotou Section of the Yellow River, it could be found that the concentration of each species for the selected heavy metals in the tributaries were obviously high than those in the main stream which was also indicated the exogenous heavy metals inputs from the industrial wastewater of the Baotou City. By the comparison of the two tributaries, the pollution superposition of Pb and Zn from the Kundulun River were higher than those from the Sidaosha River, while the pollution superposition of Cu from the Sidaosha River was higher than those from the Kundulun River. The correlation analysis indicated that there were negative correlation between the mean grain sizes and the concentrations of organic matter, carbonate, Fe oxide and Mn oxide in the sediments with different grain sizes from the main stream of the Yellow River. The results showed that there were significant negative correlation found between the organic matter and the mean grain sizes with the correlation coefficient of -0.975 (p<0.005); and there were significant negative correlation found between the carbonate and the mean grain sizes with the correlation coefficient of -0.944 (p<0.05). The contribution of mass fraction for different size sediments to speciation distribution was different. The ordre of contribution rate for different grain sizes sediments was D5 ＞ D4, D2 ＞ D3 ＞ D1 at Site A; D4＞ D3, D2 ＞ D5 ＞ D1 at Site B; D3 D5 ＞ D4, D2 ＞D1 at Site C; D5D4＞D3＞D2＞D1 at Site D. Overall, the contribution on heavy metal speciation in sediments from Baotou Section of the Yellow River was mainly caused by the size fractions of D5 and D3. Thus, the potential ecological risk caused by the different grain size sediments can not be ignored, especially the size fractions of D5 and D3.
The Yellow River contains large amounts of sands, resulting in a peculiar hydraulic condition which is characterized by a magnificent interface between the particulates and water. In addition, Baotou section of the Yellow River suffers from severe heavy metal pollution receiving the industrial discharges from the Baotou city. Therefore, this study was carried out on Baotou section of the Yellow River based on its representativeness on the mechanism of heavy metal adsorption on watersediment interface, and on the heavy metal spatial distribution, mobilization, transformation, and accumulation effects in sediments. Because of their persistence in the environment, heavy metals often pose threats to aquatic lives and plants in the environment. Based on the theories and methods of environmental geochemistry, biogeochemistry, pollution ecology and modern sedimentology, the speciation distribution characters of heavy metals such as Cu, Pb, Zn in the different grain sizes sediments and the contribution of the different grain sizes sediments on the concentrations of different heavy metals speciation were discussed in this work. The results indicated that the bound to FeMn oxide was the dominant form of nonsteadystate of Cu, Pb, and Zn in different grain sizes sediments from the Yellow River, and there were the concentration order of the bound to FeMn oxide ＞ the bound to carbonate ＞ the bound to organic matter for Cu and Pb, while the bound to FeMn oxide ＞ the bound to organic matter ＞ the bound to carbonate for Zn. The grainsize effects of the different species for the selected heavy metals were observed in this work which was the results of particle size and active components such as organic matter, carbonate and FeMn oxides in different grain sizes sediments from the studied section of the Yellow River. In all of the factors, the particle sizes played a key role in affecting the concentration of different species of the selected heavy metals. Based on the experiments, it was found that the bound to FeMn oxides was the dominant form in different size fractions of sediments from Baotou Section of the Yellow River, and its concentration was mainly influenced by the content of Fe oxide in different grain sizes sediments from the studied section of the Yellow River. The results also showed that the concentrations of each species were ranked as Zn＞Pb＞Cu in the same size fraction sediments, which was not consistent with the background values of heavy metals in sediment from the midstream of the Yellow River. The differences found in this work indicated that there were exogenous heavy metals inputs from the industrial wastewater of the Baotou City from another point of view. The dominant forms of Cu, Pb and Zn are FeMn oxides bound and bound to organic matter in sediments from the tributaries of the Yellow River. From the comparison between the main stream and the tributaries of the Baotou Section of the Yellow River, it could be found that the concentration of each species for the selected heavy metals in the tributaries were obviously high than those in the main stream which was also indicated the exogenous heavy metals inputs from the industrial wastewater of the Baotou City. By the comparison of the two tributaries, the pollution superposition of Pb and Zn from the Kundulun River were higher than those from the Sidaosha River, while the pollution superposition of Cu from the Sidaosha River was higher than those from the Kundulun River. The correlation analysis indicated that there were negative correlation between the mean grain sizes and the concentrations of organic matter, carbonate, Fe oxide and Mn oxide in the sediments with different grain sizes from the main stream of the Yellow River. The results showed that there were significant negative correlation found between the organic matter and the mean grain sizes with the correlation coefficient of -0.975 (p<0.005); and there were significant negative correlation found between the carbonate and the mean grain sizes with the correlation coefficient of -0.944 (p<0.05). The contribution of mass fraction for different size sediments to speciation distribution was different. The ordre of contribution rate for different grain sizes sediments was D5 ＞ D4, D2 ＞ D3 ＞ D1 at Site A; D4＞ D3, D2 ＞ D5 ＞ D1 at Site B; D3 D5 ＞ D4, D2 ＞D1 at Site C; D5D4＞D3＞D2＞D1 at Site D. Overall, the contribution on heavy metal speciation in sediments from Baotou Section of the Yellow River was mainly caused by the size fractions of D5 and D3. Thus, the potential ecological risk caused by the different grain size sediments can not be ignored, especially the size fractions of D5 and D3.
2011, 29(4): 783-792.
Abstract:
In the past more than ten years, distribution and prediction of lowstand sandbodies of LST had been put too much emphasis on during sequence stratigraphy research and petroleum exploration in continental faulted basins. However, the questions about petroleum reservoirs formation of highstand sandbodies of HST were rarely studied. As a result, petroleum exploration of highstand sandbodies of HST was directly restricted. Erlian Basin is located in the northmidland of Inner Mongolia Autonomous Region of China and is composed of many small faulted lacustrine basins of early Crataceous. In general, highstand delta system is well developed and formed the main sandstone reservoir in the gentle slop of faulted lacustrine basins. The petroleum exploration practice shows that highstand delta system that developed widely in gentle slopes, together with specific structural settings, can made many types of play and favorable petroleum accumulation zone. As a result, there is a good prospect that different reservoirs in the gentle slop overlap vertically each other and distribute laterally in a large area. The paper takes an example of Jiergalangtu Sag, which is one of the most representative faulted sags in Erlian Basin, to discuss thoroughly the depositional characteristics and petroleum reservoirs formation conditions of highstand delta system.
〓〓The Lower Crataceous in the gentle of Jiergalangtu Sag can be divided into five thirdorder sequences that are, respectively, named as SQ1, SQ2, SQ3, SQ4 and SQ5 from bottom to top. SQ1, SQ2, SQ3 and SQ4 are lacustrine sequence and the highstand sandbodies of HST of three sequence such as SQ1, SQ2 and SQ3 are the most oilbearing reservoir. Based on sequence stratigraphy analysis of early Crataceous, according to the result of characteristics of borehole lithology and log, cores observation, sedimentary facies of single well and seismic facies analysis, and so on. two types of coarse clastic highstand delta system that consist of fan delta and braided delta are divided in lacustrine sequence. The fan delta system is mainly distributed in HST of SQ1 and its sedimentary facies belts are imperfect. Its main part is the fan delta front subfacies, while the fan delta plain subfacies is difficult to be preserved because of latter erosion of the top strata of SQ1. The braided delta system is well formed in HST of SQ2 and SQ3. Its sedimentary facies belts, including braided delta plain, braided delta front and prebraided delta subfacies, are completely developed. Two different types of the highstand delta system of above have characteristics of multiphasic and inherited formation. In the end, there are two sandbodies concentrating areas in the neighborhood of Well Ji 45 and Well Ji 36 that located respectively in the north and south of the gentle slop.
〓〓After more than twenty years of exploration, two types and eight kinds of oil pools, including structural reservoir, lithologic and stratigraphic reservoir, have been discovered in the gentle slop. According to the stratigraphic position of reservoirs and the distribution character of different traps in gentle slope, and combing with types of oil pools that have been discovered, three plays that are closely associated with hightstand delta system have been respectively divided. In the vertical direction, they are named as SQ1 play of stratigraphic traps, SQ2 play of lithologic traps and SQ3 play of structural and complex traps. On the basis of distribution character of the plays, petroleum accumulation zones in different domains such as structural reservoir, lithologic and stratigraphic reservoir, etc. are finally predicted. It advances that the inner belt of the gentle slope is favorable petroleum accumulation zone of lithologic and stratigraphic reservoir, while the center and outer belts of the gentle slope are favorable petroleum accumulation zone of structural reservoir. Vertically and laterally, the distribution laws of the plays and petroleum accumulation zones provide scientific reference for evaluation and exploration on the whole. Now, through petroleum exploration that regard the highstand delta systems as the main targets, reserves have been discovered on a large scale and a good effect have been made in the inner, center and outer belts of the gentle slope. This example encourages increased focus on petroleum exploration potential of the highstand sandbodies of HST in faulted lacustrine basins and provides useful reference for petroleum exploration of numerous similar faulted basins in the east of China.
In the past more than ten years, distribution and prediction of lowstand sandbodies of LST had been put too much emphasis on during sequence stratigraphy research and petroleum exploration in continental faulted basins. However, the questions about petroleum reservoirs formation of highstand sandbodies of HST were rarely studied. As a result, petroleum exploration of highstand sandbodies of HST was directly restricted. Erlian Basin is located in the northmidland of Inner Mongolia Autonomous Region of China and is composed of many small faulted lacustrine basins of early Crataceous. In general, highstand delta system is well developed and formed the main sandstone reservoir in the gentle slop of faulted lacustrine basins. The petroleum exploration practice shows that highstand delta system that developed widely in gentle slopes, together with specific structural settings, can made many types of play and favorable petroleum accumulation zone. As a result, there is a good prospect that different reservoirs in the gentle slop overlap vertically each other and distribute laterally in a large area. The paper takes an example of Jiergalangtu Sag, which is one of the most representative faulted sags in Erlian Basin, to discuss thoroughly the depositional characteristics and petroleum reservoirs formation conditions of highstand delta system.
〓〓The Lower Crataceous in the gentle of Jiergalangtu Sag can be divided into five thirdorder sequences that are, respectively, named as SQ1, SQ2, SQ3, SQ4 and SQ5 from bottom to top. SQ1, SQ2, SQ3 and SQ4 are lacustrine sequence and the highstand sandbodies of HST of three sequence such as SQ1, SQ2 and SQ3 are the most oilbearing reservoir. Based on sequence stratigraphy analysis of early Crataceous, according to the result of characteristics of borehole lithology and log, cores observation, sedimentary facies of single well and seismic facies analysis, and so on. two types of coarse clastic highstand delta system that consist of fan delta and braided delta are divided in lacustrine sequence. The fan delta system is mainly distributed in HST of SQ1 and its sedimentary facies belts are imperfect. Its main part is the fan delta front subfacies, while the fan delta plain subfacies is difficult to be preserved because of latter erosion of the top strata of SQ1. The braided delta system is well formed in HST of SQ2 and SQ3. Its sedimentary facies belts, including braided delta plain, braided delta front and prebraided delta subfacies, are completely developed. Two different types of the highstand delta system of above have characteristics of multiphasic and inherited formation. In the end, there are two sandbodies concentrating areas in the neighborhood of Well Ji 45 and Well Ji 36 that located respectively in the north and south of the gentle slop.
〓〓After more than twenty years of exploration, two types and eight kinds of oil pools, including structural reservoir, lithologic and stratigraphic reservoir, have been discovered in the gentle slop. According to the stratigraphic position of reservoirs and the distribution character of different traps in gentle slope, and combing with types of oil pools that have been discovered, three plays that are closely associated with hightstand delta system have been respectively divided. In the vertical direction, they are named as SQ1 play of stratigraphic traps, SQ2 play of lithologic traps and SQ3 play of structural and complex traps. On the basis of distribution character of the plays, petroleum accumulation zones in different domains such as structural reservoir, lithologic and stratigraphic reservoir, etc. are finally predicted. It advances that the inner belt of the gentle slope is favorable petroleum accumulation zone of lithologic and stratigraphic reservoir, while the center and outer belts of the gentle slope are favorable petroleum accumulation zone of structural reservoir. Vertically and laterally, the distribution laws of the plays and petroleum accumulation zones provide scientific reference for evaluation and exploration on the whole. Now, through petroleum exploration that regard the highstand delta systems as the main targets, reserves have been discovered on a large scale and a good effect have been made in the inner, center and outer belts of the gentle slope. This example encourages increased focus on petroleum exploration potential of the highstand sandbodies of HST in faulted lacustrine basins and provides useful reference for petroleum exploration of numerous similar faulted basins in the east of China.
2011, 29(4): 798-808.
Abstract:
The dominant period of basin formation is defined as the period with the strongest tectonic movements, the largest extent of subsidence and the best development of source rocks. The sedimentary period of the 3rd member (Shasan, E2s3) and 4th member (Shasi, E2s4) of Shahejie Formation is the dominant period for basin formation. There were many episodes of volcanic movements during Cenozoic in Liaohe Depression, forming distribution of volcanic rocks with many series and types, which changes with the tectonic center and has the less strong activity in the earlier stages. The volcanic movements in the dominant period of Liaohe depression are abnormally strong and the appearances of volcanic rocks are frequent. The reservoirs which are altered by structural fractures and the corrosion and dissolution by formation water are favorable for oil and gas accumulation. The superposition in plane and the alternation in profile provide enough provision conditions of oil and gas sources for volcanic rock reservoirs. Furthermore, the volcanic rocks from dominant period of basin are of large thickness, widespread distribution and various traps and accumulation types, owning many advantages for oil and/or gas accumulation in many respects. The volcanic rock reservoirs for oil and/or gas in the areas of Huangshatuo and Oulituozi are typical representations among the above favorable reservoirs. The volcanic rocks from the dominant period of basin formation with favorable combination of oil and/or gas accumulation, enriching the content of oil and /or gas accumulation and the types of oil and /or gas exploration, are the important field for hydrocarbon discovery and exploration.
The dominant period of basin formation is defined as the period with the strongest tectonic movements, the largest extent of subsidence and the best development of source rocks. The sedimentary period of the 3rd member (Shasan, E2s3) and 4th member (Shasi, E2s4) of Shahejie Formation is the dominant period for basin formation. There were many episodes of volcanic movements during Cenozoic in Liaohe Depression, forming distribution of volcanic rocks with many series and types, which changes with the tectonic center and has the less strong activity in the earlier stages. The volcanic movements in the dominant period of Liaohe depression are abnormally strong and the appearances of volcanic rocks are frequent. The reservoirs which are altered by structural fractures and the corrosion and dissolution by formation water are favorable for oil and gas accumulation. The superposition in plane and the alternation in profile provide enough provision conditions of oil and gas sources for volcanic rock reservoirs. Furthermore, the volcanic rocks from dominant period of basin are of large thickness, widespread distribution and various traps and accumulation types, owning many advantages for oil and/or gas accumulation in many respects. The volcanic rock reservoirs for oil and/or gas in the areas of Huangshatuo and Oulituozi are typical representations among the above favorable reservoirs. The volcanic rocks from the dominant period of basin formation with favorable combination of oil and/or gas accumulation, enriching the content of oil and /or gas accumulation and the types of oil and /or gas exploration, are the important field for hydrocarbon discovery and exploration.
2011, 29(4): 622-630.
Abstract:
In order to knowing the relationship between the uplifting of Longmenshan Orogen and the filling characteristic of western Sichuan forelandlike basin during late Triassic, this article guided by sequence stratigraphy and sedimentology, integrated researched the outcrops, cores, then detailed studied the tectonic sequence filling characteristic in western Sichuan forelandlike Basin, founding when the setting of western Sichuan forelandlike Basin changed form marine to continental, and how was the stage. The main achievements as follow were obtained:
①From late Triassic to Jurassic, the environment of western Sichuan forelandlike basin was difference ,at the beginning ,the setting was marine, then changed to transition ,finally changed to continental environment, and the key stage was Anxian tectonic movement.
②The tectonic movement of Longmenshan orogenisc belt was eposide, the movement of each part of Longmenshan orogenisc belt was different form late Triassic to Jurassic, and the adjacent area's setting was different too.So the sedimentary models built up in different place or at the different time was difference.
③During the Ma’antang Stage(TS1BE), tectonic movement of Longmenshan orogenisc belt was weak and entire underwater ,mixed shelf is the mainly setting of the western Sichuan foreland baisn and sponge reefs found in the Anxian district. During the Xiaotangzi Stage(TS1BW), the north part of Longmenshan orogenisc belt uplifted firstly and marine delta found in the corresponding place of western Sichuan foreland basin.
During the stage of TS2BE, tectonic movement of the north part of Longmenshan orogenisc belt rivived , which led sedimentary structures with rapid filling characters forming in the northwest part of western Sichuan forelandlike basin, and tectonic movement of the middle part and the south part of Longmenshan orogenisc belt remainly quiet. In this situation, form west to east, marine delta to coastalshallow sea setting formed in the northwest Sichuan forelandlike baisn ,and coastalshallow sea to marine delta setting formed in the other place. During the stage of TS2BW, the south part of Longmenshan orogenisc belt uplifted ,too. The fragmentary material stripped form the south part and the north part of Longmenshan orogenisc belt were transported into the western Sichuan forelandlike basin. During this time ,tectonic movement of the middle part of Longmenshan orogenisc belt was not obvious, the environment of western Sichuan forelandlike basin remain transition.
When the time come to the end of TS2BW and the begin of TS3BE, the middle part of Longmenshan orogenisc belt uplifted, and the sea water dismiss form the western Sichuan forelandlike basin.After that, fluvial delta and lake were the mainly setting of western Sichuan forelandlike basin.
In order to knowing the relationship between the uplifting of Longmenshan Orogen and the filling characteristic of western Sichuan forelandlike basin during late Triassic, this article guided by sequence stratigraphy and sedimentology, integrated researched the outcrops, cores, then detailed studied the tectonic sequence filling characteristic in western Sichuan forelandlike Basin, founding when the setting of western Sichuan forelandlike Basin changed form marine to continental, and how was the stage. The main achievements as follow were obtained:
①From late Triassic to Jurassic, the environment of western Sichuan forelandlike basin was difference ,at the beginning ,the setting was marine, then changed to transition ,finally changed to continental environment, and the key stage was Anxian tectonic movement.
②The tectonic movement of Longmenshan orogenisc belt was eposide, the movement of each part of Longmenshan orogenisc belt was different form late Triassic to Jurassic, and the adjacent area's setting was different too.So the sedimentary models built up in different place or at the different time was difference.
③During the Ma’antang Stage(TS1BE), tectonic movement of Longmenshan orogenisc belt was weak and entire underwater ,mixed shelf is the mainly setting of the western Sichuan foreland baisn and sponge reefs found in the Anxian district. During the Xiaotangzi Stage(TS1BW), the north part of Longmenshan orogenisc belt uplifted firstly and marine delta found in the corresponding place of western Sichuan foreland basin.
During the stage of TS2BE, tectonic movement of the north part of Longmenshan orogenisc belt rivived , which led sedimentary structures with rapid filling characters forming in the northwest part of western Sichuan forelandlike basin, and tectonic movement of the middle part and the south part of Longmenshan orogenisc belt remainly quiet. In this situation, form west to east, marine delta to coastalshallow sea setting formed in the northwest Sichuan forelandlike baisn ,and coastalshallow sea to marine delta setting formed in the other place. During the stage of TS2BW, the south part of Longmenshan orogenisc belt uplifted ,too. The fragmentary material stripped form the south part and the north part of Longmenshan orogenisc belt were transported into the western Sichuan forelandlike basin. During this time ,tectonic movement of the middle part of Longmenshan orogenisc belt was not obvious, the environment of western Sichuan forelandlike basin remain transition.
When the time come to the end of TS2BW and the begin of TS3BE, the middle part of Longmenshan orogenisc belt uplifted, and the sea water dismiss form the western Sichuan forelandlike basin.After that, fluvial delta and lake were the mainly setting of western Sichuan forelandlike basin.
2011, 29(4): 644-657.
Abstract:
South China is one of the most complex area with continental reconstruction. Under the evolution background of tectonic regime and heat system, different basin types had been shaped with the distinguishing feature of identical phase prototype basins coming to being combined and distinct phase archetype basins being superposed. Generally, South China has two stage prototypes of marine facies original mold from Palaeozoic Era to Early Indosinian and Mesocenzoic terrestrial facies antetype; the former being labeled by fluctuating sea level, being accompanied by ingression and regression of the sea, being presented by relatively integral cyclic depositional series, and shaping the marine facies prototype basin, and the latter undergoing relatively frequent tectonic events, having multiphase tectonic reworking on marine facies prototype basins and overlapping above last term prototype, creating varied conditions of bearing, storing, and capping. For JinhuaQuzhou basin is typical representation of Mesocenozoic land facies prototype basins, being situated in kernel place of South China, by studying its key elements of prototype and recognizing entirety through part, theoretical references can be provided for researching tectonic setting evolution history and filling history of Southeast China and even the whole South China, guiding denotation on the aspect of oil and gas exploration activity.
JinhuaQuzhou Basin is one of the late Mesozoic rifted basins in Southeast China. It developed on the Premesozoic metamorphosed fold basement, mainly including three structural units of northern shallow depression zone, central uplift belt and southern hollow zone. Making use of analytic approach of basin prototype, tectonic events, deep seated structure, provenance, subsiding history, depocenter, basin boundary structure and cessation of deposition, and so on, were studied. JQ basin had undergone several evolutionary phases of early intracontinental compressing, late early Crataceous extending and drafting, late Crataceous depression, suppression of last stage of Crataceous and reformation of later stage. From research above, basin filling material was coming from ablation due to incipient fold and uplift of PreMesozoic formation and weathering denudation of mountain mass with the background of late period drafting, 〖JP2〗confirming that JQ basin had experienced uplifting and denuding events attributing to the mechanism conversion from extruding to pulling. These events had important affection on the shaping of rifting and half grabenlike basin. Sedimentation and subsidence center was in the vicinity of Quzhou with more or less translational migration during the three palaeolithofacies stages. From the study above, we can see that JQ basin has favorable oil and gas foreground, and these four structural traps of Qianjia, Shuiting, Yangtang and Jiangtang have major prospecting potentiality.〖JP〗
It is the property of local area that JinhuaQuzhou basin has tectonic framework of "one uplift and two depressions " with the northeastern strike direction. Being combined with the territorial structural framework, JinhuaQuzhou basin was controlled by westeastern basement tectonics of ageold Asian domain and restrained by deep seated structure. Kinetics contributing factor of every structural zoning of the basin presenting northeastern distribution was intimately related with the tectonic regime of age old Pacific Ocean. Since the sedimentation of Cretaceous Period, basin building and evolving main part had been controlled by crossfeed relationship of late Mesozoic structure, magma, deep lying and the basin itself of Southeast China, being affected by PreMesozoic mountain building and tectonic regime of age old Pacific Ocean. JiangshanShaoxing faulted zone was the important geotectonic unit border that had been governing areal structure, inner basin building and depositional sources of JinhuaQuzhou basin.
South China is one of the most complex area with continental reconstruction. Under the evolution background of tectonic regime and heat system, different basin types had been shaped with the distinguishing feature of identical phase prototype basins coming to being combined and distinct phase archetype basins being superposed. Generally, South China has two stage prototypes of marine facies original mold from Palaeozoic Era to Early Indosinian and Mesocenzoic terrestrial facies antetype; the former being labeled by fluctuating sea level, being accompanied by ingression and regression of the sea, being presented by relatively integral cyclic depositional series, and shaping the marine facies prototype basin, and the latter undergoing relatively frequent tectonic events, having multiphase tectonic reworking on marine facies prototype basins and overlapping above last term prototype, creating varied conditions of bearing, storing, and capping. For JinhuaQuzhou basin is typical representation of Mesocenozoic land facies prototype basins, being situated in kernel place of South China, by studying its key elements of prototype and recognizing entirety through part, theoretical references can be provided for researching tectonic setting evolution history and filling history of Southeast China and even the whole South China, guiding denotation on the aspect of oil and gas exploration activity.
JinhuaQuzhou Basin is one of the late Mesozoic rifted basins in Southeast China. It developed on the Premesozoic metamorphosed fold basement, mainly including three structural units of northern shallow depression zone, central uplift belt and southern hollow zone. Making use of analytic approach of basin prototype, tectonic events, deep seated structure, provenance, subsiding history, depocenter, basin boundary structure and cessation of deposition, and so on, were studied. JQ basin had undergone several evolutionary phases of early intracontinental compressing, late early Crataceous extending and drafting, late Crataceous depression, suppression of last stage of Crataceous and reformation of later stage. From research above, basin filling material was coming from ablation due to incipient fold and uplift of PreMesozoic formation and weathering denudation of mountain mass with the background of late period drafting, 〖JP2〗confirming that JQ basin had experienced uplifting and denuding events attributing to the mechanism conversion from extruding to pulling. These events had important affection on the shaping of rifting and half grabenlike basin. Sedimentation and subsidence center was in the vicinity of Quzhou with more or less translational migration during the three palaeolithofacies stages. From the study above, we can see that JQ basin has favorable oil and gas foreground, and these four structural traps of Qianjia, Shuiting, Yangtang and Jiangtang have major prospecting potentiality.〖JP〗
It is the property of local area that JinhuaQuzhou basin has tectonic framework of "one uplift and two depressions " with the northeastern strike direction. Being combined with the territorial structural framework, JinhuaQuzhou basin was controlled by westeastern basement tectonics of ageold Asian domain and restrained by deep seated structure. Kinetics contributing factor of every structural zoning of the basin presenting northeastern distribution was intimately related with the tectonic regime of age old Pacific Ocean. Since the sedimentation of Cretaceous Period, basin building and evolving main part had been controlled by crossfeed relationship of late Mesozoic structure, magma, deep lying and the basin itself of Southeast China, being affected by PreMesozoic mountain building and tectonic regime of age old Pacific Ocean. JiangshanShaoxing faulted zone was the important geotectonic unit border that had been governing areal structure, inner basin building and depositional sources of JinhuaQuzhou basin.
2011, 29(4): 665-676.
Abstract:
Based on detailed analysis of cores, logs, and seismic data, ten lithofacies were indentified, including megathick and thick massive sandstones, thick normalgraded sandstones, thick inversegraded sandstones, parallel and tabular crossstratified sandstones, slumped and deformed sandstones, thin sandstone interlayers, thin mudstonesandstone interbeds, thick siltstones, thick mudstones, and deepwater limestones. They can be organized into five lithofacies associations. These are sandstonedominated, mudstonedominated, mudstonesandstone interbed, siltstone and deepwater limestone associations. Based on the analyses of lithofacies and their associations, the depositional system of the reservoir in the Zhujiang Formation, Liwan 31 field is identified as submarine fan. Four microfacies are further recognized within the fan based on detailed analysis, including channels (including main channels in the inner fan and distributary channels in the middle fan), interchannel, leveeoverbank, outer fan and basin microfacies. Facies analysis allows to reconstruct the depositional model of the deepwater fan. During relative sealevel fall, a basinfloor fan formed as sediments from rivers or shelf margin deltas were further transported down slope and into the basin under gravity flows. During the ensuing relative sealevel rise, a slope fan was deposited as the system stepped back. The lower part of the Zhujiang Formation, mainly sandstonedominated associations, is inner fan and middleouter fan deposits of the basinfloor and the slope fan respectively. The upper part, mainly mudstonedominated associations, siltstone associations, and deepwater associations are outer fan deposits of the slope fan and basin deposits. Along with the transgression, submarine fan was finally replaced by pelagic deposits.
Based on detailed analysis of cores, logs, and seismic data, ten lithofacies were indentified, including megathick and thick massive sandstones, thick normalgraded sandstones, thick inversegraded sandstones, parallel and tabular crossstratified sandstones, slumped and deformed sandstones, thin sandstone interlayers, thin mudstonesandstone interbeds, thick siltstones, thick mudstones, and deepwater limestones. They can be organized into five lithofacies associations. These are sandstonedominated, mudstonedominated, mudstonesandstone interbed, siltstone and deepwater limestone associations. Based on the analyses of lithofacies and their associations, the depositional system of the reservoir in the Zhujiang Formation, Liwan 31 field is identified as submarine fan. Four microfacies are further recognized within the fan based on detailed analysis, including channels (including main channels in the inner fan and distributary channels in the middle fan), interchannel, leveeoverbank, outer fan and basin microfacies. Facies analysis allows to reconstruct the depositional model of the deepwater fan. During relative sealevel fall, a basinfloor fan formed as sediments from rivers or shelf margin deltas were further transported down slope and into the basin under gravity flows. During the ensuing relative sealevel rise, a slope fan was deposited as the system stepped back. The lower part of the Zhujiang Formation, mainly sandstonedominated associations, is inner fan and middleouter fan deposits of the basinfloor and the slope fan respectively. The upper part, mainly mudstonedominated associations, siltstone associations, and deepwater associations are outer fan deposits of the slope fan and basin deposits. Along with the transgression, submarine fan was finally replaced by pelagic deposits.
2011, 29(4): 689-694.
Abstract:
In our country as the lower frequency of land and shallow water exploration for oil and gas, deep water oil and gas exploration is playing more important role. Big reservoir body becomes the target of deepwater oil and gas exploration, because the deepwater oil and gas exploration has some characteristics, such as greater risks and higher investment. Central canyon, which comes from Yinggehai basin and pass through Qiongdongnan basin and enter into the xisha trough, lies in the deepwater area of Qiongdongnan basin and is mainly formed at 10.5 Ma, 5.5 Ma and 4.2 Ma. With an area of more than 50 000 km2, central canyon can be a target of deepwater oil and gas exploration.
In the central canyon, leveeoverbank sediments are abundant. Deepwater leveeoverbank has received considerable attention in the petroleum industry because of having good reservoirs. In order to conduct the prospect for central canyon, this article has analyzed the shape and control factors of leveeoverbank deposited in the central canyon by using 3D seismic profile and RMS attribute. After that, the sediment model is summed up and the foreground of prospect is analyzed. The result has shown below:
1. leveeoverbank sediments in the central canyon developed at least eight times, and have many micro facies such as crevasse splay, overflow splay and levee. In the cross seismic profiles, leveeoverbank sediments represent wedge shape with strong amplitude, intermediate frequency and midgood continuity, and combining with channel has shown "gullwing" shape. In the plane, the overall shape of leveeoverbank sediments is elongate and trends roughly parallel to the channel. Its area of single sand body could reach 17 km2.
2. In the central canyon, leveeoverbank sediments is mainly controlled by province and ancient physiognomy. The grain size whether sandrich or mudrich is mainly decided by province. The position is mainly decided by ancient physiognomy. The pond accommodate space is afforded for leveeoverbank to be deposited in the area where has fluctuation variation. On the opposite, in the incline area, there is no accommodation and leveeoverbank cannot deposit.
3. Leveeoverbank sediments which has many deposition time and large single sand body can be ideal stratigraphic traps and it could accumulate oil and gas if it cooperate with fault or "gas chimney". Leveeoverbank sediments have well foreground for prospect.
In our country as the lower frequency of land and shallow water exploration for oil and gas, deep water oil and gas exploration is playing more important role. Big reservoir body becomes the target of deepwater oil and gas exploration, because the deepwater oil and gas exploration has some characteristics, such as greater risks and higher investment. Central canyon, which comes from Yinggehai basin and pass through Qiongdongnan basin and enter into the xisha trough, lies in the deepwater area of Qiongdongnan basin and is mainly formed at 10.5 Ma, 5.5 Ma and 4.2 Ma. With an area of more than 50 000 km2, central canyon can be a target of deepwater oil and gas exploration.
In the central canyon, leveeoverbank sediments are abundant. Deepwater leveeoverbank has received considerable attention in the petroleum industry because of having good reservoirs. In order to conduct the prospect for central canyon, this article has analyzed the shape and control factors of leveeoverbank deposited in the central canyon by using 3D seismic profile and RMS attribute. After that, the sediment model is summed up and the foreground of prospect is analyzed. The result has shown below:
1. leveeoverbank sediments in the central canyon developed at least eight times, and have many micro facies such as crevasse splay, overflow splay and levee. In the cross seismic profiles, leveeoverbank sediments represent wedge shape with strong amplitude, intermediate frequency and midgood continuity, and combining with channel has shown "gullwing" shape. In the plane, the overall shape of leveeoverbank sediments is elongate and trends roughly parallel to the channel. Its area of single sand body could reach 17 km2.
2. In the central canyon, leveeoverbank sediments is mainly controlled by province and ancient physiognomy. The grain size whether sandrich or mudrich is mainly decided by province. The position is mainly decided by ancient physiognomy. The pond accommodate space is afforded for leveeoverbank to be deposited in the area where has fluctuation variation. On the opposite, in the incline area, there is no accommodation and leveeoverbank cannot deposit.
3. Leveeoverbank sediments which has many deposition time and large single sand body can be ideal stratigraphic traps and it could accumulate oil and gas if it cooperate with fault or "gas chimney". Leveeoverbank sediments have well foreground for prospect.
2011, 29(4): 704-711.
Abstract:
By use of strata study on the field outcrops and microfacies analysis indoor, types of gravityflow deposits have been found in Maokou Formation Middle Permian, western Hubei province, which developed in carbonate slope depositional environment, from top to bottom slump deposits, debris flow deposits, particle flow deposits have been regonized, slump deposits developed in the Cili Jiang Ya section, Hunan province, particle flow and debris flow developed in the Ziqiu section Changyang country. Slump sediments is composed of the clutter angular subangular calcirudite, poor sorting, grainsupported, shortrange slump slided off from the platform margin; debris flow deposits formed of the calcirudite, gravel limestone, bioclastic micritic limestone, gravel is slightly alignment and subangular, sub rounded, gravel gradually reduced from bottom to top; particle flow is composed of the gravel limestone sediments, wackstone with miliolids, which developed 2 to 3 cycles and graded layer and wavy bedding. Gravity flow deposits in the study area controlled by the tectonic evolution, the characteristics of its spatial and temporal distribution of the area in the middle Permian is consistent with platformbasin deposition pattern, and it has certain significance for the Permian sedimentary evolution in the study area.
By use of strata study on the field outcrops and microfacies analysis indoor, types of gravityflow deposits have been found in Maokou Formation Middle Permian, western Hubei province, which developed in carbonate slope depositional environment, from top to bottom slump deposits, debris flow deposits, particle flow deposits have been regonized, slump deposits developed in the Cili Jiang Ya section, Hunan province, particle flow and debris flow developed in the Ziqiu section Changyang country. Slump sediments is composed of the clutter angular subangular calcirudite, poor sorting, grainsupported, shortrange slump slided off from the platform margin; debris flow deposits formed of the calcirudite, gravel limestone, bioclastic micritic limestone, gravel is slightly alignment and subangular, sub rounded, gravel gradually reduced from bottom to top; particle flow is composed of the gravel limestone sediments, wackstone with miliolids, which developed 2 to 3 cycles and graded layer and wavy bedding. Gravity flow deposits in the study area controlled by the tectonic evolution, the characteristics of its spatial and temporal distribution of the area in the middle Permian is consistent with platformbasin deposition pattern, and it has certain significance for the Permian sedimentary evolution in the study area.
2011, 29(4): 724-733.
Abstract:
Changbei gas field is located in Yishan Slope of the northern center of the Ordos Basin, China. The main pay zone reservoir is Upper Paleozoic Lower Permian Shanxi P1S2 quartz arenite, which deposited in distributary channel of delta plain. The reservoir is low porosity low permeability tight reservoir with average porosity of 5.2% and average permeability of 0.7×103 μm2in a current depth of 2 700~2 950 m. Integrated study on depositional environment, lithology, diagenesis and tectonic background has been conducted. The reasons cause this low porosity low permeability tight reservoir features are considered as the following two factors. (1) On one hand, the reservoir was deposited in a coaly bearing acid environment of deltaic distributary channel, the original pore water is acid water with non saturated calcium carbonate, which can not form earlier cementation within the sandstone reservoir. However, compaction has significantly reduce the original pore and pore volume. On the other hand, this acid diagenesis environment cause large amounts of secondary quartz cementation fill the pores left out during compaction of sandstone reservoir. This is the main reasons cause the low porosity low permeability tight reservoir features in the region. Observation from thin section indicate that calcium carbonate cementation is not developed in the pore of sandstone reservoir especially in the earlier stage, the average component of calcium carbonate cementation is 1%~3%， authigenic kaolinite cementation is well developed with an average component of 7%~10%，illite segmentation is also less developed <3%，secondary quartz cementation well develop, mostly reach Ⅱ—Ⅲ level with an average component of 5%~10%，some layer can reach 10%~18% and maximum is 23%，this phenomenon indicated the acid diagenesis environment of P1S2 quartz arenite reservoir in Changbei gas field. (2) Tectonic study indicated that Changbei gas field is located in Ordos Basin tectonically stable at the time when Lower Permian Shanxi Formation was deposited. No tectonic movement and significant structure activities developed so that the formation layers are flat and rare faults and folds seen in the Changbei field. Buried history analysis also indicated that there is no apparently uplift and subsidence after P1S2 Shanxi Formation deposited. Underground water especially organic acid and CO2 acid water is not active, and pore is reduced by compaction and silicon dioxide cementation, acid water can't effectively dissolve the reservoir and displacement of materials in the pore. On the other hand, there are few dissolvable components e.g. feldspar (<3%), lithic and carbonate cementation in the rock, hence limited amount of secondary pores generated, this is the second reason that cause poor quality reservoir in Changbei gas field.
Changbei gas field is located in Yishan Slope of the northern center of the Ordos Basin, China. The main pay zone reservoir is Upper Paleozoic Lower Permian Shanxi P1S2 quartz arenite, which deposited in distributary channel of delta plain. The reservoir is low porosity low permeability tight reservoir with average porosity of 5.2% and average permeability of 0.7×103 μm2in a current depth of 2 700~2 950 m. Integrated study on depositional environment, lithology, diagenesis and tectonic background has been conducted. The reasons cause this low porosity low permeability tight reservoir features are considered as the following two factors. (1) On one hand, the reservoir was deposited in a coaly bearing acid environment of deltaic distributary channel, the original pore water is acid water with non saturated calcium carbonate, which can not form earlier cementation within the sandstone reservoir. However, compaction has significantly reduce the original pore and pore volume. On the other hand, this acid diagenesis environment cause large amounts of secondary quartz cementation fill the pores left out during compaction of sandstone reservoir. This is the main reasons cause the low porosity low permeability tight reservoir features in the region. Observation from thin section indicate that calcium carbonate cementation is not developed in the pore of sandstone reservoir especially in the earlier stage, the average component of calcium carbonate cementation is 1%~3%， authigenic kaolinite cementation is well developed with an average component of 7%~10%，illite segmentation is also less developed <3%，secondary quartz cementation well develop, mostly reach Ⅱ—Ⅲ level with an average component of 5%~10%，some layer can reach 10%~18% and maximum is 23%，this phenomenon indicated the acid diagenesis environment of P1S2 quartz arenite reservoir in Changbei gas field. (2) Tectonic study indicated that Changbei gas field is located in Ordos Basin tectonically stable at the time when Lower Permian Shanxi Formation was deposited. No tectonic movement and significant structure activities developed so that the formation layers are flat and rare faults and folds seen in the Changbei field. Buried history analysis also indicated that there is no apparently uplift and subsidence after P1S2 Shanxi Formation deposited. Underground water especially organic acid and CO2 acid water is not active, and pore is reduced by compaction and silicon dioxide cementation, acid water can't effectively dissolve the reservoir and displacement of materials in the pore. On the other hand, there are few dissolvable components e.g. feldspar (<3%), lithic and carbonate cementation in the rock, hence limited amount of secondary pores generated, this is the second reason that cause poor quality reservoir in Changbei gas field.
2011, 29(4): 744-751.
Abstract:
As unique tight reservoirs in China, the middleupper Jurassic sandstones in central Sichuan basin occur at presentday burial depth of 1 500~3 000 m and they are characterized by ultralow porosity (average below 5%) and ultra-low permeability (average below 1×10-3 μm2) that fail to match their burial depth. Microscopic observation and statistics of relative contribution of compaction and cementation to porosity loss indicate that intensive compaction is responsible for the anomalous tightness of these sandstones. Furthermore，utilizing the research method of sandstone dynamical diagenesis theory, based on the analysis of original sandstone components and basin diagenetic dynamic factors, the mechanism of intensive compaction of Middle and Lower Jurassic sandstones in the study area has been discussed. It is suggested that fine grain size and high ductile fragments content are the internal cause, while the basin diagenetic dynamics characteristics of deep paleoburial, high paleogeothermal field and late oil emplacement are considered as the external cause.
〓〓Mechanisms of diagenesis and porosity evolution of some sandstone reservoirs are quite complex in superimposed basins in western China. In one of these complex cases, this study of origin mechanism of anomalous tightness of Middle and Lower Jurassic sandstone reservoirs in central Sichuan Basin shows that the sandstone dynamical diagenesis theory and method can integrally and systematically take original sandstone components and all basin diagenetic dynamics factors (structure, thermal flow, pore fluid, etc.) into account, and which can well resolve such difficult questions in complex sandstone reservoirs.
As unique tight reservoirs in China, the middleupper Jurassic sandstones in central Sichuan basin occur at presentday burial depth of 1 500~3 000 m and they are characterized by ultralow porosity (average below 5%) and ultra-low permeability (average below 1×10-3 μm2) that fail to match their burial depth. Microscopic observation and statistics of relative contribution of compaction and cementation to porosity loss indicate that intensive compaction is responsible for the anomalous tightness of these sandstones. Furthermore，utilizing the research method of sandstone dynamical diagenesis theory, based on the analysis of original sandstone components and basin diagenetic dynamic factors, the mechanism of intensive compaction of Middle and Lower Jurassic sandstones in the study area has been discussed. It is suggested that fine grain size and high ductile fragments content are the internal cause, while the basin diagenetic dynamics characteristics of deep paleoburial, high paleogeothermal field and late oil emplacement are considered as the external cause.
〓〓Mechanisms of diagenesis and porosity evolution of some sandstone reservoirs are quite complex in superimposed basins in western China. In one of these complex cases, this study of origin mechanism of anomalous tightness of Middle and Lower Jurassic sandstone reservoirs in central Sichuan Basin shows that the sandstone dynamical diagenesis theory and method can integrally and systematically take original sandstone components and all basin diagenetic dynamics factors (structure, thermal flow, pore fluid, etc.) into account, and which can well resolve such difficult questions in complex sandstone reservoirs.
2011, 29(4): 767-775.
Abstract:
Classically, the grain size of sediment samples is determined by the sieve method for the coarse fractions and by the pipette method, based on the Stokes' sedimentation rates, for the fine fractions. Results from the pipette method are compared with results from laser diffraction size analysis using a set of randomly selected 106 surface sediments which are collected from the Eastern South China Sea. The aim of this research is to calibrate systematically the grain size and content of clay fraction and sediment type achieved from laser diffractometry.
〓〓The contents of sand, silt, and clay in sediments of eastern South China Sea with depth more than 2 000 m were 3.7%, 42.4% and 53.9%, respectively, obtained from standard sedimentation method, and 9.3%, 61.1%, 29.6% respectively from laser diffractometry. The deviation of contents of silt and clay fraction obtained from the two methods is about 20%. The sediment types obtained from the eastern South China Sea obtained from sedimentation method are essentially silty clay of 69.8%, and secondly is clay 19.8%. There is very small amount of other types, only 11.4%. The main sediment type based on laser diffractometry is clayey silt of 89.6%, and secondly is sandy silt of about 10.4%, there is no any other types obtained. The agreement of sediment type between the two methods is only 21.7%, which means there are significant discrepancies for the contents of clay fraction achieved from two different methods.
〓〓Therefore, it is not possible to compare the contents of different grain size and sediment type obtained from the two methods without calibration. The grain size of clay fraction from laser method was calibrated to <0.01 mm, and 0.063~0.01 mm for silt correspondingly. The contents of clay and silt fraction are 54.2% and 36.2%, respectively, after calibration, which is very close to the result of 52.1% for the clay fraction and 42.3% for the silt fraction from the sedimentation method. The agreement between sedimentation method and calibrated laser method is 91.5%. Most of clayey silt is calibrated to silty clay. The correlation coefficients are 0.3203 for the silt fraction and 0.3347 for the clay fraction after calibration. The relationship appears to be positively strong, indicating that the calibration for grain size and content of clay fraction is successful.
〓〓However, there is no distinct improvement for the content of clay and silt fraction calibrated according to regressive equation. The contents are 29.1% and 62.2%, respectively. The discrepancy between the content of clay and silt fraction from two methods is 20%, but there is lower amplitude of variation. The agreement of sediment type with regressive method is only 21.7%, which means the discrepancy arrives at 78.3%, indicating that calibration with regressive equation for content of clay and silt fraction and sediment type. The research suggested that after the grain size were calibrated to <0.01 mm for clay fraction and 0.063~0.01 mm for silt fraction, the contents of clay and silt fraction and sediment type agreed well with those from sedimentation method. There is almost no improvement using regressive calibration.
Classically, the grain size of sediment samples is determined by the sieve method for the coarse fractions and by the pipette method, based on the Stokes' sedimentation rates, for the fine fractions. Results from the pipette method are compared with results from laser diffraction size analysis using a set of randomly selected 106 surface sediments which are collected from the Eastern South China Sea. The aim of this research is to calibrate systematically the grain size and content of clay fraction and sediment type achieved from laser diffractometry.
〓〓The contents of sand, silt, and clay in sediments of eastern South China Sea with depth more than 2 000 m were 3.7%, 42.4% and 53.9%, respectively, obtained from standard sedimentation method, and 9.3%, 61.1%, 29.6% respectively from laser diffractometry. The deviation of contents of silt and clay fraction obtained from the two methods is about 20%. The sediment types obtained from the eastern South China Sea obtained from sedimentation method are essentially silty clay of 69.8%, and secondly is clay 19.8%. There is very small amount of other types, only 11.4%. The main sediment type based on laser diffractometry is clayey silt of 89.6%, and secondly is sandy silt of about 10.4%, there is no any other types obtained. The agreement of sediment type between the two methods is only 21.7%, which means there are significant discrepancies for the contents of clay fraction achieved from two different methods.
〓〓Therefore, it is not possible to compare the contents of different grain size and sediment type obtained from the two methods without calibration. The grain size of clay fraction from laser method was calibrated to <0.01 mm, and 0.063~0.01 mm for silt correspondingly. The contents of clay and silt fraction are 54.2% and 36.2%, respectively, after calibration, which is very close to the result of 52.1% for the clay fraction and 42.3% for the silt fraction from the sedimentation method. The agreement between sedimentation method and calibrated laser method is 91.5%. Most of clayey silt is calibrated to silty clay. The correlation coefficients are 0.3203 for the silt fraction and 0.3347 for the clay fraction after calibration. The relationship appears to be positively strong, indicating that the calibration for grain size and content of clay fraction is successful.
〓〓However, there is no distinct improvement for the content of clay and silt fraction calibrated according to regressive equation. The contents are 29.1% and 62.2%, respectively. The discrepancy between the content of clay and silt fraction from two methods is 20%, but there is lower amplitude of variation. The agreement of sediment type with regressive method is only 21.7%, which means the discrepancy arrives at 78.3%, indicating that calibration with regressive equation for content of clay and silt fraction and sediment type. The research suggested that after the grain size were calibrated to <0.01 mm for clay fraction and 0.063~0.01 mm for silt fraction, the contents of clay and silt fraction and sediment type agreed well with those from sedimentation method. There is almost no improvement using regressive calibration.
2011, 29(4): 793-797.
Abstract:
There has no the ability of generating oil and gas in the shallower strata of Dongpu sag. Developed as one of the most important transporting body, the sandstone connects deeper hydrocarbon source rocks and shallower trap, so sandstone transporting capability directly determines if or not the hydrocarbon accumulation can happen in the shallower strata. The evaluation of sandstone transporting capability is one of weak links in the study of transporting body; the micro transporting characteristics determine quality of sandstone transporting capability. Since there has defects in microscopic property measurement techniques of conventional sandstone, this article by means of the measuring software on pore diameter named Scandium in scanning electron microscope for the first time, the sizes of pore and throat of shallower strata in Dongpu sag are distinctively measured systematically in microscopic scaling. Then the longitudinal distributing characteristics are summarized. The transporting capability of the sandstone and its change are analyzed. All of these offer a new method in the study of pore structure and sandstone transporting capability. It shows those throat width and poretothroat ratios are the main factors influencing the transporting capability of shallower strata. The sequence of sandstone transporting capability more and more better are the first segment of Shahejie Fm.(Es1), to Dongying Fm.(Ed) and Guantao Fm.(Ng). However, the transporting capability in Minghuazhen Fm.(Nm) upon Guantao Fm.(Ng) is worse again; Hereby, if the others conditions of migration and accumulation are satisfied, hydrocarbon may migrate to the Guantao Formation and accumulate here.
There has no the ability of generating oil and gas in the shallower strata of Dongpu sag. Developed as one of the most important transporting body, the sandstone connects deeper hydrocarbon source rocks and shallower trap, so sandstone transporting capability directly determines if or not the hydrocarbon accumulation can happen in the shallower strata. The evaluation of sandstone transporting capability is one of weak links in the study of transporting body; the micro transporting characteristics determine quality of sandstone transporting capability. Since there has defects in microscopic property measurement techniques of conventional sandstone, this article by means of the measuring software on pore diameter named Scandium in scanning electron microscope for the first time, the sizes of pore and throat of shallower strata in Dongpu sag are distinctively measured systematically in microscopic scaling. Then the longitudinal distributing characteristics are summarized. The transporting capability of the sandstone and its change are analyzed. All of these offer a new method in the study of pore structure and sandstone transporting capability. It shows those throat width and poretothroat ratios are the main factors influencing the transporting capability of shallower strata. The sequence of sandstone transporting capability more and more better are the first segment of Shahejie Fm.(Es1), to Dongying Fm.(Ed) and Guantao Fm.(Ng). However, the transporting capability in Minghuazhen Fm.(Nm) upon Guantao Fm.(Ng) is worse again; Hereby, if the others conditions of migration and accumulation are satisfied, hydrocarbon may migrate to the Guantao Formation and accumulate here.
2011, 29(4): 809-814.
Abstract:
In order to probe into abnormal geothermal's influence on hydrocarbongeneration, we collected eight source rock samples (W008W015) from the black mudstone series of strata of Carboniferous upper Haerjiawu group on the south side of the diabase intrusion of the East Daheishan Profile in the Santanghu Basin, whose distance to the diabase rock is 20 cm, 50 cm, 100 cm, 180 cm, 300 cm, 500 cm, 1 000 cm, and 1 700 cm, respectively. Through analysis of the basic geochemical characteristics such as the atomic ratios of Ro to H/C and to O/C, the change of the chloroform bitumen "A" and total hydrocarbon of the eight samples, along with selective analysis of the chromatographic characteristics of the saturated hydrocarbon of five of them, we found that with the distance to the diabase rock greater than 180 cm, the content of Ro remains almost unchanged, however, the content of Ro significantly increases with the distance less than 180 cm; the atomic ratio of H/C in W008 and W009 is relatively small, which is 0.385 and 0.404, while from W011 to W015, the atomic ratio of H/C is about 0.5, which remains the same on the whole; the range of variation in the atomic ratio of O/C is relatively small concentrating around 0.1, and the atomic ratio of O/C in W008 and W009 is slightly smaller than adjacent samples (W010, W011); the chloroform bitumen "A" and total hydrocarbon of W008 is slightly higher than that of W009 ~ W012; from the pespective of organic saturated hydrocarbon parameters, CPI in W008, W009 and W010 is relatively small, which is obviously different from that of in W012, and W014. From the above analysis, we can conclude that the overall maturity of this source rock is rather high, and near the diabase intrusion with the distance range of 1~1.8 m, its maturity index has the trend of exceptional increase which shows the source rocks directly exposed to the intrusive rocks has a relative smaller scope of baking effect which is less than about 1.8 m.
In order to probe into abnormal geothermal's influence on hydrocarbongeneration, we collected eight source rock samples (W008W015) from the black mudstone series of strata of Carboniferous upper Haerjiawu group on the south side of the diabase intrusion of the East Daheishan Profile in the Santanghu Basin, whose distance to the diabase rock is 20 cm, 50 cm, 100 cm, 180 cm, 300 cm, 500 cm, 1 000 cm, and 1 700 cm, respectively. Through analysis of the basic geochemical characteristics such as the atomic ratios of Ro to H/C and to O/C, the change of the chloroform bitumen "A" and total hydrocarbon of the eight samples, along with selective analysis of the chromatographic characteristics of the saturated hydrocarbon of five of them, we found that with the distance to the diabase rock greater than 180 cm, the content of Ro remains almost unchanged, however, the content of Ro significantly increases with the distance less than 180 cm; the atomic ratio of H/C in W008 and W009 is relatively small, which is 0.385 and 0.404, while from W011 to W015, the atomic ratio of H/C is about 0.5, which remains the same on the whole; the range of variation in the atomic ratio of O/C is relatively small concentrating around 0.1, and the atomic ratio of O/C in W008 and W009 is slightly smaller than adjacent samples (W010, W011); the chloroform bitumen "A" and total hydrocarbon of W008 is slightly higher than that of W009 ~ W012; from the pespective of organic saturated hydrocarbon parameters, CPI in W008, W009 and W010 is relatively small, which is obviously different from that of in W012, and W014. From the above analysis, we can conclude that the overall maturity of this source rock is rather high, and near the diabase intrusion with the distance range of 1~1.8 m, its maturity index has the trend of exceptional increase which shows the source rocks directly exposed to the intrusive rocks has a relative smaller scope of baking effect which is less than about 1.8 m.
