2011 Vol. 29, No. 5
Display Method:
2011, 29(5): 815-824.
Abstract:
On the basis of observation of cores, facies analysis and grain size analysis of 226 samples from 3 core wells, the probability cumulative grain size curves features of sandy conglomerate of the upper Es4 in Yan22 block Dongying Depression are summarized, the relationships between the probability cumulative grain size curves types and the hydrodynamic conditions are studied. Conclusions are gained as follows：
(1) The relationships between the probability cumulative grain size curves shapes and the hydrodynamic conditions or fluid property are found. The research shows that the grains size curves of the nearshore subaqueous fan have the characteristics of coarsegrained, widerange and lowslope, can be classified into 3 basic patterns (e.g. "uphill arched arc" pattern, one segment pattern and "quasi drag flow" pattern) and 4 transitional patterns. The "uphill arched arc" pattern represents debris flow deposition, one segment pattern represents turbidity deposition, the transitional patterns represent the deposition of transitional fluid property.
(2) The composition characteristics of probability cumulative grain size curve patterns vary with the change of microfacies or subfacies. Inner fan of the nearshore subaqueous fan, made up of thick sandy conglomerate with mixed fabrics of main channel, is typical of “broadly uphill arched arc” pattern，that represents debris flow deposition. Middle fan mainly has two kinds of deposition: debris flow deposition and drag flow deposition. The curve type of the lowermiddle part, made up of thick coarse sandstone with massive bedding, is "approximate uphill arched arc" pattern. And the upper part, made up of parallel bedding, are "one bouncing populationone suspension population sectionstransitional zone " pattern and " one rolling populationone bouncing populationone suspension population" trisegment pattern. Outer fan has three types of curve patterns, such as "low slope trisegment" pattern, "one
bouncing populationone suspension population sectionstransitional zone "pattern, "one rolling populationone bouncing populationone suspension population" trisegment pattern and etc, the sandstones often have parallel bedding, cross bedding and graded bedding. Note that, interchannel microface is typical of "steptype" multisegment pattern that reflects the effect of flood overflow from channels.
(3) The type evolution of the grain size curve patterns in nearshore subaqueous fan sandy conglomerate is inferred in the paper. With the transportation of nearshore subaqueous fan away from origination area, subfacies develop from inner fan, middle fan to outer fan in turn. As the behavior of the fluid evolves from debris flow to drag flow, the patterns of the grain size curves may change from "broadly uphill arched arc" pattern, "slightly high slope uphill arched arc" pattern to one segment pattern, "high slope multisegment" pattern.
(4) Besides nearshore subaqueous fan, terrigenous basin has other 5 different genetic types of sandy conglomerate, such as alluvial fan, braided river delta, fan delta, deepwater turbidity fan in steep slope and turbidity fan slides from nershore sand body front. All kinds of these depositions are affected by gravity flow, they all have the characteristics of close source, quick accumulation, while the grain size curves have the same characteristics of coarsegrained, widerange and lowslope. And thus the classification of the probability cumulative grain size curve patterns mentioned in this paper may be applicable to other different genetic types of sandy conglomerate.
On the basis of observation of cores, facies analysis and grain size analysis of 226 samples from 3 core wells, the probability cumulative grain size curves features of sandy conglomerate of the upper Es4 in Yan22 block Dongying Depression are summarized, the relationships between the probability cumulative grain size curves types and the hydrodynamic conditions are studied. Conclusions are gained as follows：
(1) The relationships between the probability cumulative grain size curves shapes and the hydrodynamic conditions or fluid property are found. The research shows that the grains size curves of the nearshore subaqueous fan have the characteristics of coarsegrained, widerange and lowslope, can be classified into 3 basic patterns (e.g. "uphill arched arc" pattern, one segment pattern and "quasi drag flow" pattern) and 4 transitional patterns. The "uphill arched arc" pattern represents debris flow deposition, one segment pattern represents turbidity deposition, the transitional patterns represent the deposition of transitional fluid property.
(2) The composition characteristics of probability cumulative grain size curve patterns vary with the change of microfacies or subfacies. Inner fan of the nearshore subaqueous fan, made up of thick sandy conglomerate with mixed fabrics of main channel, is typical of “broadly uphill arched arc” pattern，that represents debris flow deposition. Middle fan mainly has two kinds of deposition: debris flow deposition and drag flow deposition. The curve type of the lowermiddle part, made up of thick coarse sandstone with massive bedding, is "approximate uphill arched arc" pattern. And the upper part, made up of parallel bedding, are "one bouncing populationone suspension population sectionstransitional zone " pattern and " one rolling populationone bouncing populationone suspension population" trisegment pattern. Outer fan has three types of curve patterns, such as "low slope trisegment" pattern, "one
bouncing populationone suspension population sectionstransitional zone "pattern, "one rolling populationone bouncing populationone suspension population" trisegment pattern and etc, the sandstones often have parallel bedding, cross bedding and graded bedding. Note that, interchannel microface is typical of "steptype" multisegment pattern that reflects the effect of flood overflow from channels.
(3) The type evolution of the grain size curve patterns in nearshore subaqueous fan sandy conglomerate is inferred in the paper. With the transportation of nearshore subaqueous fan away from origination area, subfacies develop from inner fan, middle fan to outer fan in turn. As the behavior of the fluid evolves from debris flow to drag flow, the patterns of the grain size curves may change from "broadly uphill arched arc" pattern, "slightly high slope uphill arched arc" pattern to one segment pattern, "high slope multisegment" pattern.
(4) Besides nearshore subaqueous fan, terrigenous basin has other 5 different genetic types of sandy conglomerate, such as alluvial fan, braided river delta, fan delta, deepwater turbidity fan in steep slope and turbidity fan slides from nershore sand body front. All kinds of these depositions are affected by gravity flow, they all have the characteristics of close source, quick accumulation, while the grain size curves have the same characteristics of coarsegrained, widerange and lowslope. And thus the classification of the probability cumulative grain size curve patterns mentioned in this paper may be applicable to other different genetic types of sandy conglomerate.
2011, 29(5): 835-841.
Abstract:
Heavy mineral data are widely used in the analysis of sediment source. Source rocks of different depositional stages and different source areas can be identified based on heavy mineral suites. In this study using Qtype clustering analysis, the sample group with the same or similar features in the vertical profile is identified as sediments of the same depositional stages, so each sample group is representative of a certain depositional stage or source rock. On the basis of Qtype clustering analysis, using Rtype clustering analysis, the differences among each kind of heavy mineral are available in the same depositional stage, and different heavy mineral suites are defined. The same heavy mineral suite is considered that it comes from the same source rock, and the different heavy mineral suites are used to recognize different source areas. These, the sediments with features of the same depositional stage and the same heavy mineral suite are as an independent system. Coupled with the independent system's ZTR maps, allow robust identification of specific directions of sediment source in each depositional stage. The integrated data set shows that there are four distinct sediment sources in the submember in the study area. These are the northwest source, the southwest source, the northeast source, and the east source. The directions of different sediment sources identified are in accordance with the main building directions of fans delta or alluvial fans. Using heavy mineral suites generated from cluster analysis to identify source area in the Weixinan Depression is quite effective.
Heavy mineral data are widely used in the analysis of sediment source. Source rocks of different depositional stages and different source areas can be identified based on heavy mineral suites. In this study using Qtype clustering analysis, the sample group with the same or similar features in the vertical profile is identified as sediments of the same depositional stages, so each sample group is representative of a certain depositional stage or source rock. On the basis of Qtype clustering analysis, using Rtype clustering analysis, the differences among each kind of heavy mineral are available in the same depositional stage, and different heavy mineral suites are defined. The same heavy mineral suite is considered that it comes from the same source rock, and the different heavy mineral suites are used to recognize different source areas. These, the sediments with features of the same depositional stage and the same heavy mineral suite are as an independent system. Coupled with the independent system's ZTR maps, allow robust identification of specific directions of sediment source in each depositional stage. The integrated data set shows that there are four distinct sediment sources in the submember in the study area. These are the northwest source, the southwest source, the northeast source, and the east source. The directions of different sediment sources identified are in accordance with the main building directions of fans delta or alluvial fans. Using heavy mineral suites generated from cluster analysis to identify source area in the Weixinan Depression is quite effective.
2011, 29(5): 857-865.
Abstract:
The Precambrian biosphere includes almost exclusively microbiota. Activities of benthic prokaryotes in response to the sedimentary dynamics could form the characteristic structures known as "Microbially Induced Sedimentary Structures (MISS)", arising syndepositionally from the interactions of biofilms and microbial mats with the sedimentary grains due to the variations in hydraulic parameters in siliciclastic aquatic environments. Yunmengshan Formation, belonging to Mesoproterozoic Ruyang Group, lies in the south margin of the North China Platform and consists mainly of siliciclastic sedimentary successions. MISS occur on the surface of purple or yellow sandstone interbedded with mudstone or siltstone, especially on junction surface between sandstone and mud lamination. They displayed a plenty of morphologies and were preserved in acompanying with ripple markers as usual. The wellpreserved structures include mat growth features, mat metabolism features, mat destruction features and mat decay features. In vertical section, the typical stacked mmlevel siliciclastic biolaminites consisting of alternations of dark silty mudstones and light quartz sandstone represent repeated growth and burial of mats during repeated depositional events. The dark layers also included Feoxides, sericite and dark asphaltenelike minerals which included 1 620 cm-1 and 1 340 cm-1 organic Raman shift and displayed high dimensional similarities with ethylcellulose, nylon66 and polynorbornene. The dark layers which have been found modern analogues in tidal flat and formed by the mat growth, mat metabolism and the interactions of biofilms and microbial mats with the sediments are considered to represent the remains of ancient microbial mats, whereas the light layers consist of physical process induced quartz grains. The participation of microbial mats in the accretion of the siliciclastic biolaminites is indicated by various MISS, especially mat growth and destruction structures. In the further investigation of thinsections, five types of microstructures have been found: wavy crinkled laminae, network fabrics, mat layer bound small grains, mat layer bound heavy minerals and oriented grains. Wavy crinkled laminae represent the presence of ancient biofilms or microbial mats, and caused by mat growth; oriented grains, mat layer bound small grains and network fabrics related to baffling, trapping and binding of biofilms and microbial mats; The presence of biofilms and microbial mats in the ancient environment promoted the productions of Feoxides and sericite and lined the mat layers. These microscopic units testify the presence of thick mat in moderate to low hydrodynamic disturbance and reflect the unique characters of sediments which were occupied, stabilized and fixed by microbial mats. Microstructures can mainly be preserved in the favorable ecological sites where microbial mats colonized, such as upper intertidal and lower supratidal zones. Microstructures could be used to reconstruct smallscaled facies within coastal environments, and include hints to paleoclimatological, hydrological and sedimentological conditions.
The Precambrian biosphere includes almost exclusively microbiota. Activities of benthic prokaryotes in response to the sedimentary dynamics could form the characteristic structures known as "Microbially Induced Sedimentary Structures (MISS)", arising syndepositionally from the interactions of biofilms and microbial mats with the sedimentary grains due to the variations in hydraulic parameters in siliciclastic aquatic environments. Yunmengshan Formation, belonging to Mesoproterozoic Ruyang Group, lies in the south margin of the North China Platform and consists mainly of siliciclastic sedimentary successions. MISS occur on the surface of purple or yellow sandstone interbedded with mudstone or siltstone, especially on junction surface between sandstone and mud lamination. They displayed a plenty of morphologies and were preserved in acompanying with ripple markers as usual. The wellpreserved structures include mat growth features, mat metabolism features, mat destruction features and mat decay features. In vertical section, the typical stacked mmlevel siliciclastic biolaminites consisting of alternations of dark silty mudstones and light quartz sandstone represent repeated growth and burial of mats during repeated depositional events. The dark layers also included Feoxides, sericite and dark asphaltenelike minerals which included 1 620 cm-1 and 1 340 cm-1 organic Raman shift and displayed high dimensional similarities with ethylcellulose, nylon66 and polynorbornene. The dark layers which have been found modern analogues in tidal flat and formed by the mat growth, mat metabolism and the interactions of biofilms and microbial mats with the sediments are considered to represent the remains of ancient microbial mats, whereas the light layers consist of physical process induced quartz grains. The participation of microbial mats in the accretion of the siliciclastic biolaminites is indicated by various MISS, especially mat growth and destruction structures. In the further investigation of thinsections, five types of microstructures have been found: wavy crinkled laminae, network fabrics, mat layer bound small grains, mat layer bound heavy minerals and oriented grains. Wavy crinkled laminae represent the presence of ancient biofilms or microbial mats, and caused by mat growth; oriented grains, mat layer bound small grains and network fabrics related to baffling, trapping and binding of biofilms and microbial mats; The presence of biofilms and microbial mats in the ancient environment promoted the productions of Feoxides and sericite and lined the mat layers. These microscopic units testify the presence of thick mat in moderate to low hydrodynamic disturbance and reflect the unique characters of sediments which were occupied, stabilized and fixed by microbial mats. Microstructures can mainly be preserved in the favorable ecological sites where microbial mats colonized, such as upper intertidal and lower supratidal zones. Microstructures could be used to reconstruct smallscaled facies within coastal environments, and include hints to paleoclimatological, hydrological and sedimentological conditions.
2011, 29(5): 876-888.
Abstract:
The sedimentary area of the Early Permian Taiyuan Formation in Henan Province is located in the south of north China basin and to the north of LuanchuanGushi deep fault in the North Qingling fold belt, at that time, this sedimentary basin was controlled by the tectonopaleogeographic features of the west uplift in the North China platform block. The Taiyuan Formation was a part of deposits of the NorthChina epicontinental sea or carbonate platform in the Late Paleozoic, and developed a set of deposits of the epicontinental sea characterized by the carbonate rocks intercalated some clastic rocks and coal. This section is mainly composed of gray, dark gray, thinmedium bedded bioclastic limestones, intercalated with thinmedium bedded mudstone, micritic limestone, fine sandstone, siltstones and thin coals, locally appeared light gray thick beded moderatefine grained sandstone, coarse sandstone or graywhite quartz sandstone, with very abundant body fossils, such as fusulinids, conodonts, brachiopods, corals, crinoids, bivalves and plants fossils and so on. According to the analysis of sedimentary sequence, the Taiyuan Formation can be divided into three units from bottom to top: the lower limestone unit, mainly containing 4 ~ 5 limestone layers; the middle clastic unit, dominated by sandstone and mudstone, intercalated with 1~3 layers of limestone, unstable bioclastic microcrystalline limestone; the upper limestone unit, composed of 2 ~ 3 layers of limestone, locally, 4 ~ 5 layers. Based on the isoline trend analysis including the thickness of the formation and carbonate rock and the ratio of sand to mudstone, along with the composition and distribution features of ichnofossils, facies fossils and sedimentary assemblage types, 5 sedimentary facies (tidalflat, lagoon , barrier island or sand bar, restricted carbonate platform and open carbonate platform facies) , 12 kinds of sedimentary types, 3 sedimentary assemblage types and 3 types of lithofacies areas as the micritic limestone and mudstone lithofacies area of restricted flatformtidal flat setting, limestone and clastic lithofacies area of open platformtidallagoon setting and limestone and clastic lithofacies area of open platformbarrier islandtidal flat setting can be suggested. The Lithofacies palaeogeographic characteristics of Henan province during the deposit of the Taiyuan Formation display：(1) The marine invasion is widespread and limestone of shallow sea facies is almost throughout the whole sedimentary region；(2)Sealine extended eastward and southward to LingbaoLuoningSongxianFangchengBiyang zone；(3)Old land areas are situated the Funiu mountain to sorthwest of this basin and Zhongtiao Mountain to west of this basin；(4)Paleotopography shows steep in the west, gentle in the east, high relief in the northwest, and low relief in the southeast；(5)The sedimentary zone of largest thickness of this formation is in the northeast and east of this basin；(6)Seawater invasion was from the east and northeast, and regression from northwest to southeast. In the Taiyuan Formation sedimentary period, the basement terrain of this sedimentary basin was relatively gentle and sea water was frequently progressive and regressive, thereby, the interbeds of carbonate rocks of the restricted epicontinental sedimentary environment and coalbearing clastic rock of tidal flat sedimentary setting were generated, and the larger area peat flat were developed in the coastal plain in Henan Province, and the coal layers with industrial value were formed in many parts.
The sedimentary area of the Early Permian Taiyuan Formation in Henan Province is located in the south of north China basin and to the north of LuanchuanGushi deep fault in the North Qingling fold belt, at that time, this sedimentary basin was controlled by the tectonopaleogeographic features of the west uplift in the North China platform block. The Taiyuan Formation was a part of deposits of the NorthChina epicontinental sea or carbonate platform in the Late Paleozoic, and developed a set of deposits of the epicontinental sea characterized by the carbonate rocks intercalated some clastic rocks and coal. This section is mainly composed of gray, dark gray, thinmedium bedded bioclastic limestones, intercalated with thinmedium bedded mudstone, micritic limestone, fine sandstone, siltstones and thin coals, locally appeared light gray thick beded moderatefine grained sandstone, coarse sandstone or graywhite quartz sandstone, with very abundant body fossils, such as fusulinids, conodonts, brachiopods, corals, crinoids, bivalves and plants fossils and so on. According to the analysis of sedimentary sequence, the Taiyuan Formation can be divided into three units from bottom to top: the lower limestone unit, mainly containing 4 ~ 5 limestone layers; the middle clastic unit, dominated by sandstone and mudstone, intercalated with 1~3 layers of limestone, unstable bioclastic microcrystalline limestone; the upper limestone unit, composed of 2 ~ 3 layers of limestone, locally, 4 ~ 5 layers. Based on the isoline trend analysis including the thickness of the formation and carbonate rock and the ratio of sand to mudstone, along with the composition and distribution features of ichnofossils, facies fossils and sedimentary assemblage types, 5 sedimentary facies (tidalflat, lagoon , barrier island or sand bar, restricted carbonate platform and open carbonate platform facies) , 12 kinds of sedimentary types, 3 sedimentary assemblage types and 3 types of lithofacies areas as the micritic limestone and mudstone lithofacies area of restricted flatformtidal flat setting, limestone and clastic lithofacies area of open platformtidallagoon setting and limestone and clastic lithofacies area of open platformbarrier islandtidal flat setting can be suggested. The Lithofacies palaeogeographic characteristics of Henan province during the deposit of the Taiyuan Formation display：(1) The marine invasion is widespread and limestone of shallow sea facies is almost throughout the whole sedimentary region；(2)Sealine extended eastward and southward to LingbaoLuoningSongxianFangchengBiyang zone；(3)Old land areas are situated the Funiu mountain to sorthwest of this basin and Zhongtiao Mountain to west of this basin；(4)Paleotopography shows steep in the west, gentle in the east, high relief in the northwest, and low relief in the southeast；(5)The sedimentary zone of largest thickness of this formation is in the northeast and east of this basin；(6)Seawater invasion was from the east and northeast, and regression from northwest to southeast. In the Taiyuan Formation sedimentary period, the basement terrain of this sedimentary basin was relatively gentle and sea water was frequently progressive and regressive, thereby, the interbeds of carbonate rocks of the restricted epicontinental sedimentary environment and coalbearing clastic rock of tidal flat sedimentary setting were generated, and the larger area peat flat were developed in the coastal plain in Henan Province, and the coal layers with industrial value were formed in many parts.
2011, 29(5): 906-916.
Abstract:
During the deposition of the Miocene Zhujiang Formation, the HZ Sag in the Pearl River Mouth Basin, South China Sea, was a stably deposited shelf setting. A largescale paleoPearl River water system was developed in the western part of the study area and provided abundant terrestrial clastic deposits for the largescale Pearl River delta. A case study on sequence PSQ6 has been carried out in this paper. The depositional slope break of sequence PSQ6 is characterized by a certain developing scale of about 4 km slope width, 2060 m height difference and 80 km transverse distribution range. Depositional slope breaks were mainly developed during the ending time of the depositional period of highstand systems tract delta of underlying sequence. A regional "ditchtrough" system was formed along the area between depositional slope break and carbonate buildup in the east of prodeltaic subfacies, thus provided a favorable paleogeomorphic setting for the deposition and preservation of PSQ6 forced regressive wedge systems tract(FRWST) and furthermore controlled the development of regional forced regressive wedge in shelf environment. The forced regressive sandbodies are easily formed due to the "ditchtrough" paleogeomorphic setting in shelf environment. The prograded sandbodies directly cover the shallow marine mudstones of the underlying sequence highstand systems tract and are overlaid with the darkcolor mudstones of transgressive and highstand systems tracts, thus a favorable source reservoir caprock assemblage is formed and stratigraphiclithologic hydrocarbon accumulations usually occur in these areas.
During the deposition of the Miocene Zhujiang Formation, the HZ Sag in the Pearl River Mouth Basin, South China Sea, was a stably deposited shelf setting. A largescale paleoPearl River water system was developed in the western part of the study area and provided abundant terrestrial clastic deposits for the largescale Pearl River delta. A case study on sequence PSQ6 has been carried out in this paper. The depositional slope break of sequence PSQ6 is characterized by a certain developing scale of about 4 km slope width, 2060 m height difference and 80 km transverse distribution range. Depositional slope breaks were mainly developed during the ending time of the depositional period of highstand systems tract delta of underlying sequence. A regional "ditchtrough" system was formed along the area between depositional slope break and carbonate buildup in the east of prodeltaic subfacies, thus provided a favorable paleogeomorphic setting for the deposition and preservation of PSQ6 forced regressive wedge systems tract(FRWST) and furthermore controlled the development of regional forced regressive wedge in shelf environment. The forced regressive sandbodies are easily formed due to the "ditchtrough" paleogeomorphic setting in shelf environment. The prograded sandbodies directly cover the shallow marine mudstones of the underlying sequence highstand systems tract and are overlaid with the darkcolor mudstones of transgressive and highstand systems tracts, thus a favorable source reservoir caprock assemblage is formed and stratigraphiclithologic hydrocarbon accumulations usually occur in these areas.
2011, 29(5): 926-934.
Abstract:
Future environment evolution is a great composition of global change research. High resolution paleoenvironment study can help us to understand the rules of past global change and provides scientific basis for forecasting future environment evolution. As a special type of crater lake, maar lake has unique advantages in forming and conserving high resolution geological record. Elementary assemblages of the lake sediment are not only affected by depositional environment, but also linked to geochemical property of the element. There is not straightforward connection between most of the elements and the environment variation due to the complexity of depositional environment and various changes after deposition. The combination of element and element ratios can magnify the response to climate change, thus weaken the effect of disturbing factors. The Huguangyan maar lake (21°9′N, 110°17′E) is located 18 km southwest of Zhanjiang City, Guangdong province. In November, 2009, we sampled two parallel long cores using UWITEC platform and a piston corer in the western part of the Huguangyan maar lake where the water depth is 16.2m (N 21°08′38.28″, E 110°16′45.66″)
. The drill core for this study is 855 cm long. The core was split along the axle wire before elementary analysis, elementary analysis is carried by Xray fluorescence spectrometer at State Key Laboratory of Marine Geology of Tongji University, the measuring space is 1 cm. Age model is obtained through comparison with previous study. Fe/Mn ratios, Rb/Sr ratios, Sr intensities and 550℃ loss on ignition (LOI) are good indicators of environmental change: Fe/Mn ratios can reflect water depth variation due to different sensibilities toward oxidoreduction condition, Rb/Sr ratios can reflect weathering intensity within the drainage basin, 550℃ loss on ignition (LOI) is an indicator of lake productivity, thus reflect the climate indirectly. Through high resolution investigation of above indicators, we reconstructed Holocene paleoenvironment evolution history of the Huguangyan area, paleoenvironment revolution at Huguangyan area since 11 000 cal a BP can be divided into four stages: stage Ⅰ, 11 000~7 800 cal a BP, the climate was warm and wet; stage Ⅱ, 7 800~5 600 cal a BP, the climate became cold and dry rapidly; stage Ⅲ, 5 600~2 000 cal a BP, it was relative warm and wet, but not as warm as early Holocene; stage Ⅳ, 2 000 cal a BP as yet, the climate became dry gradually. The results show that early Holocene is the Holocene optimum, the climate became relatively dry since the mid Holocene. This pattern is consistent with pollen record also from Huguangyan maar lake and other records from low latitude area of the northern hemisphere, which indicates the global nature of the orbital forcing of the Holocene monsoon. There are affiliations and differences between cold events reflected by Huguangyan Maar lake sediment and North Atlantic icerafted debris, which suggests that climate shift at low latitude area has certain linkage with North Atlantic area. Low latitude processes, such as monsoon and ENSO, are influencing factors that affected Holocene evolution at Huguangyan area. Holocene paleoenvironment evolution at low latitude is the result of superposition of low latitude processes and high latitude processes, which makes the mechanism of climate change at low latitude area more complicated.
Future environment evolution is a great composition of global change research. High resolution paleoenvironment study can help us to understand the rules of past global change and provides scientific basis for forecasting future environment evolution. As a special type of crater lake, maar lake has unique advantages in forming and conserving high resolution geological record. Elementary assemblages of the lake sediment are not only affected by depositional environment, but also linked to geochemical property of the element. There is not straightforward connection between most of the elements and the environment variation due to the complexity of depositional environment and various changes after deposition. The combination of element and element ratios can magnify the response to climate change, thus weaken the effect of disturbing factors. The Huguangyan maar lake (21°9′N, 110°17′E) is located 18 km southwest of Zhanjiang City, Guangdong province. In November, 2009, we sampled two parallel long cores using UWITEC platform and a piston corer in the western part of the Huguangyan maar lake where the water depth is 16.2m (N 21°08′38.28″, E 110°16′45.66″)
. The drill core for this study is 855 cm long. The core was split along the axle wire before elementary analysis, elementary analysis is carried by Xray fluorescence spectrometer at State Key Laboratory of Marine Geology of Tongji University, the measuring space is 1 cm. Age model is obtained through comparison with previous study. Fe/Mn ratios, Rb/Sr ratios, Sr intensities and 550℃ loss on ignition (LOI) are good indicators of environmental change: Fe/Mn ratios can reflect water depth variation due to different sensibilities toward oxidoreduction condition, Rb/Sr ratios can reflect weathering intensity within the drainage basin, 550℃ loss on ignition (LOI) is an indicator of lake productivity, thus reflect the climate indirectly. Through high resolution investigation of above indicators, we reconstructed Holocene paleoenvironment evolution history of the Huguangyan area, paleoenvironment revolution at Huguangyan area since 11 000 cal a BP can be divided into four stages: stage Ⅰ, 11 000~7 800 cal a BP, the climate was warm and wet; stage Ⅱ, 7 800~5 600 cal a BP, the climate became cold and dry rapidly; stage Ⅲ, 5 600~2 000 cal a BP, it was relative warm and wet, but not as warm as early Holocene; stage Ⅳ, 2 000 cal a BP as yet, the climate became dry gradually. The results show that early Holocene is the Holocene optimum, the climate became relatively dry since the mid Holocene. This pattern is consistent with pollen record also from Huguangyan maar lake and other records from low latitude area of the northern hemisphere, which indicates the global nature of the orbital forcing of the Holocene monsoon. There are affiliations and differences between cold events reflected by Huguangyan Maar lake sediment and North Atlantic icerafted debris, which suggests that climate shift at low latitude area has certain linkage with North Atlantic area. Low latitude processes, such as monsoon and ENSO, are influencing factors that affected Holocene evolution at Huguangyan area. Holocene paleoenvironment evolution at low latitude is the result of superposition of low latitude processes and high latitude processes, which makes the mechanism of climate change at low latitude area more complicated.
2011, 29(5): 946-952.
Abstract:
Jing River estuaryTongguan is the most unstable section of Wei River.The bend developed sharply and disappeared rapidly,and river course changed frequently as well.The processing of the morphological changing was reconstructed based on both kinds of terrain materials during 19152000A.D. and the modulation in the error of surveying and mapping on roc map.The trend was described by fractal dimension (D), the rang of index D changing is \[1.0432, 1.0774\]. Relatively,under the natural environment, the shape of Wei River(Jing River estuaryTongguan) is a dynamic equilibrium during the 43 years(19151958), the D displayed balance.Wei River is the biggest tributaries.
It has the ability to adjust the shape itself. The D went up high sharply during 19692000A.D.Although many corners of Jing River estuaryTongguan have disappeared, the shape of Weihe downstream has became complicated consistently. However, in the last 50a, unreasonable human activity, such as Sanmenxia project, building dam and flood plain reclamation, leading to the retrogressive deposition and restricting the moveable space of Wei River, growing of D rapidly in this period. The changing of D displayed the low reach of Wei River lost the function of adjusting morphology since 1960s.According to the historical records, there was a morphological changing during 1860s, the low reach trend to more curved, maybe during the 1860s1960s the rang of D is larger than the decades after 1960s.With the method of Fractal Geometry (Benoit Mandelbrod put forward in 1975,the morphology between the mix form and the regulate form),this research precisely shows the development of river style in the process of describing changing in the river on the plaint,it also suitable for the processing of the message which contains river morphology in terrain with a abundance of source.
Jing River estuaryTongguan is the most unstable section of Wei River.The bend developed sharply and disappeared rapidly,and river course changed frequently as well.The processing of the morphological changing was reconstructed based on both kinds of terrain materials during 19152000A.D. and the modulation in the error of surveying and mapping on roc map.The trend was described by fractal dimension (D), the rang of index D changing is \[1.0432, 1.0774\]. Relatively,under the natural environment, the shape of Wei River(Jing River estuaryTongguan) is a dynamic equilibrium during the 43 years(19151958), the D displayed balance.Wei River is the biggest tributaries.
It has the ability to adjust the shape itself. The D went up high sharply during 19692000A.D.Although many corners of Jing River estuaryTongguan have disappeared, the shape of Weihe downstream has became complicated consistently. However, in the last 50a, unreasonable human activity, such as Sanmenxia project, building dam and flood plain reclamation, leading to the retrogressive deposition and restricting the moveable space of Wei River, growing of D rapidly in this period. The changing of D displayed the low reach of Wei River lost the function of adjusting morphology since 1960s.According to the historical records, there was a morphological changing during 1860s, the low reach trend to more curved, maybe during the 1860s1960s the rang of D is larger than the decades after 1960s.With the method of Fractal Geometry (Benoit Mandelbrod put forward in 1975,the morphology between the mix form and the regulate form),this research precisely shows the development of river style in the process of describing changing in the river on the plaint,it also suitable for the processing of the message which contains river morphology in terrain with a abundance of source.
2011, 29(5): 953-961.
Abstract:
The characteristics of present abnormal high formation pressure (AHFP) in Xujiahe Formation of central Sichuan Basin were obtained based on the measured formation pressure. The formation pressure of main reservoirs obviously shows high formation pressure or AHFP at present. Bajiaochang gas field is a typical AHFP gas field with pressure coefficient between 1.7 and 2.0, while the others belong to high formation pressure gas fields with pressure coefficient between 1.2 and 1.6. This paper use coupled fluid flow compaction method to reconstruct the pressure evolution of the major reservoirs in Xujiahe Formation. This method could perfectly consider the changes of porosity, permeability and fluid volume in the reservoirs, which could perfectly reconstruct the pressure evolution history. Thermal history is a key parameter during reconstructing the pressure evolution, so this paper reconstructs thermal history by using vitrinite reflectance based on Easy% Ro model. The pressure evolution history of the major reservoirs were reconstructed according to relevant parameters and constrained in measured formation pressure. The evolution of formation pressure in Xujiahe Formation can be divided into three stages: (1) normal pressure before 150 Ma; (2) pressure increase and AHFP accumulation between 150 Ma and 100 Ma. The formation pressure and pressure coefficient gradually increased during this period. The formation pressure got to maximum with pressure coefficient between 1.1 and 1.6 at about 100 Ma; (3) pressure release but AHFP accumulation after 100 Ma. Both the formation pressure and the hydrostatic pressure decreased, but the hydrostatic pressure decreased more than formation pressure, so the pressure coefficient still increase and finally reach between 1.4 and 2.0. The origin of abnormal pressure was analyzed based on the reconstructed formation pressure incorporated burial history and maturity evolution history. It was found that the hydrocarbon charging and the hydrostatic pressure decrease during strata erosion were the main origin of AHFP, while the temperature decrease during strata erosion was main origin for the decrease of formation pressure at later period. AHFP is conducive to the hydrocarbon migration and accumulation in this area. With the characteristics of strong heterogeneity in the reservoirs, the development of AHFP was main force for hydrocarbon migration and accumulation through the dense barriers. The fluid migration is nondarcy flow in low permeable reservoir which must overcome restart pressure. In this case, the overpressure was necessary for hydrocarbon migration. The decrease of formation pressure at later period was beneficial to desolution of dissolved gas and desorption of coal bed methane in Xujiahe Formation, which enhanced the gas accumulation efficiency. To a certain extent, it reduces the requirements for gas kitchen, forming a series of large gas fields under the condition of source rock deficiency of Xujiahe Formation in central Sichuan Basin
The characteristics of present abnormal high formation pressure (AHFP) in Xujiahe Formation of central Sichuan Basin were obtained based on the measured formation pressure. The formation pressure of main reservoirs obviously shows high formation pressure or AHFP at present. Bajiaochang gas field is a typical AHFP gas field with pressure coefficient between 1.7 and 2.0, while the others belong to high formation pressure gas fields with pressure coefficient between 1.2 and 1.6. This paper use coupled fluid flow compaction method to reconstruct the pressure evolution of the major reservoirs in Xujiahe Formation. This method could perfectly consider the changes of porosity, permeability and fluid volume in the reservoirs, which could perfectly reconstruct the pressure evolution history. Thermal history is a key parameter during reconstructing the pressure evolution, so this paper reconstructs thermal history by using vitrinite reflectance based on Easy% Ro model. The pressure evolution history of the major reservoirs were reconstructed according to relevant parameters and constrained in measured formation pressure. The evolution of formation pressure in Xujiahe Formation can be divided into three stages: (1) normal pressure before 150 Ma; (2) pressure increase and AHFP accumulation between 150 Ma and 100 Ma. The formation pressure and pressure coefficient gradually increased during this period. The formation pressure got to maximum with pressure coefficient between 1.1 and 1.6 at about 100 Ma; (3) pressure release but AHFP accumulation after 100 Ma. Both the formation pressure and the hydrostatic pressure decreased, but the hydrostatic pressure decreased more than formation pressure, so the pressure coefficient still increase and finally reach between 1.4 and 2.0. The origin of abnormal pressure was analyzed based on the reconstructed formation pressure incorporated burial history and maturity evolution history. It was found that the hydrocarbon charging and the hydrostatic pressure decrease during strata erosion were the main origin of AHFP, while the temperature decrease during strata erosion was main origin for the decrease of formation pressure at later period. AHFP is conducive to the hydrocarbon migration and accumulation in this area. With the characteristics of strong heterogeneity in the reservoirs, the development of AHFP was main force for hydrocarbon migration and accumulation through the dense barriers. The fluid migration is nondarcy flow in low permeable reservoir which must overcome restart pressure. In this case, the overpressure was necessary for hydrocarbon migration. The decrease of formation pressure at later period was beneficial to desolution of dissolved gas and desorption of coal bed methane in Xujiahe Formation, which enhanced the gas accumulation efficiency. To a certain extent, it reduces the requirements for gas kitchen, forming a series of large gas fields under the condition of source rock deficiency of Xujiahe Formation in central Sichuan Basin
2011, 29(5): 970-979.
Abstract:
Source rocks in deep water basins in the north of South China Sea are obviously different from the passive margin basins in Atlantic Ocean. Mesozoic lacustrine source rock in the rifting sequence and marine source rock in the postrift depression are the main source rocks in the passive margin basins of Atlantic Ocean, and their organic matters in lacustrine and marine source rocks all mainly came from aquatic lower organisms. There maybe exist three kinds of source rocks, including lacustrine source rock, transitional coalbearing source rock and marine source rock in deep water basins in the north of South China Sea, but the correlation of oil/gas and source showed that Tertiary coalbearing source rocks in transitional sequence is the main source rock there. Organic matters in transitional coalbearing source rock and marine source rock mainly came from terrestrial higher plants in the north of South China Sea, and fluvial deltaic system is one of the very important factors for controlling the growth of terrestrial higher plants and abundance of organic matter. Because of the influence of the Paleopearl River, coalbearing source rock of Enping Formation distribute relatively widespread and stable in the Pearl River Mouth basin. But there is no large river system, and fandelta is the main type of delta, so coalbearing source rock of Yacheng Formation distributed relatively limited in Qiongdongnan basin. The formation of marine source rocks is influenced by the quantity of terrestrial organic matter and accumulation and reservation of organic matter. Because of the difference of paleogeography condition between the Pearl River Mouth basin and Qiongdongnan basin, origin of terrestrial organic matter in the Pearl River Mouth basin is much more abundant than Qiongdongnan basin, and the content of total organic carbon for marine source rock in the Pearl River Mouth basin is higher than the same geological time source rocks in Qiongdongnan basin. Because the supply of terrestrial organic matter decrease from land to ocean, so the organic matter content of marine source rock also lower from land to ocean. Seen from the distribution of source rocks in north of South China Sea, source rocks with relative high organic matter content mainly distributed in the surrounding area of basin or depression, they are mainly composed of coalbearing source rock, also include some marine source rock with abundant organic matter, but the organic matter content is popularly low in the depocenter of basin or depression, the surrounding area of basin or depression is more profit for oil and gas exploration.
Source rocks in deep water basins in the north of South China Sea are obviously different from the passive margin basins in Atlantic Ocean. Mesozoic lacustrine source rock in the rifting sequence and marine source rock in the postrift depression are the main source rocks in the passive margin basins of Atlantic Ocean, and their organic matters in lacustrine and marine source rocks all mainly came from aquatic lower organisms. There maybe exist three kinds of source rocks, including lacustrine source rock, transitional coalbearing source rock and marine source rock in deep water basins in the north of South China Sea, but the correlation of oil/gas and source showed that Tertiary coalbearing source rocks in transitional sequence is the main source rock there. Organic matters in transitional coalbearing source rock and marine source rock mainly came from terrestrial higher plants in the north of South China Sea, and fluvial deltaic system is one of the very important factors for controlling the growth of terrestrial higher plants and abundance of organic matter. Because of the influence of the Paleopearl River, coalbearing source rock of Enping Formation distribute relatively widespread and stable in the Pearl River Mouth basin. But there is no large river system, and fandelta is the main type of delta, so coalbearing source rock of Yacheng Formation distributed relatively limited in Qiongdongnan basin. The formation of marine source rocks is influenced by the quantity of terrestrial organic matter and accumulation and reservation of organic matter. Because of the difference of paleogeography condition between the Pearl River Mouth basin and Qiongdongnan basin, origin of terrestrial organic matter in the Pearl River Mouth basin is much more abundant than Qiongdongnan basin, and the content of total organic carbon for marine source rock in the Pearl River Mouth basin is higher than the same geological time source rocks in Qiongdongnan basin. Because the supply of terrestrial organic matter decrease from land to ocean, so the organic matter content of marine source rock also lower from land to ocean. Seen from the distribution of source rocks in north of South China Sea, source rocks with relative high organic matter content mainly distributed in the surrounding area of basin or depression, they are mainly composed of coalbearing source rock, also include some marine source rock with abundant organic matter, but the organic matter content is popularly low in the depocenter of basin or depression, the surrounding area of basin or depression is more profit for oil and gas exploration.
2011, 29(5): 986-993.
Abstract:
Trace elements of oilbearing fluid inclusion in sixteen Silurian oilcontaining sandstones from ten wells in Tazhong area were performed by inductively coupled plasma mass spectroscopy（ICPMS）, the distribution characteristics were analyzed, and their demonstrative geological significance were furthermore discussed. The results show that for the same sample, each trace element abundance is small to one order of magnitude, and large to hundreds orders of magnitude, but for the different samples, the difference times of the same element abundance is ordinarily lower than one order of magnitude, some element(Ni and Ti)may reach up to one order of magnitude or more. In the same well field, the abundance distribution of part trace elements of samples from different wells present preferable regularity, such as Ni, Fe, Al, Cu, Ti, Mg, Cr and so on, and the distribution rules of Ni, Cu and Ti show a certain similarity, whereas the distribution of Cr, Al, Mn and Mg are similar to each other. As a whole, the distribution rule of main trace elements is that the abundance is increasing from downstructure location to structural high. Of all the samples, the ratios of V/Ni is generally low, range from 0.044 to 0.683, most of samples are less than 0.5, lower V/Ni ratio and high Fe content represent a strong reductive depositional environment. Variation characteristics of the single trace elements, such as Ni, Cu, Αl and Ti, obviously disappear a noticeable rule and indicated that oil migrated from Well Tazhong 69 and Well Tazhong 15 to Well Tazhong 16 and Well Tazhong 161, namely Silurian hydrocarbons in Tazhong area migrated towards structural high or stratigraphic pinch out direction, from northwest to southeast on the plane, which also reflected by the trace element suite. Therefore, trace elements of oilbearing fluid inclusion can provide effective evidence for studying oil and gas migratory direction.
Trace elements of oilbearing fluid inclusion in sixteen Silurian oilcontaining sandstones from ten wells in Tazhong area were performed by inductively coupled plasma mass spectroscopy（ICPMS）, the distribution characteristics were analyzed, and their demonstrative geological significance were furthermore discussed. The results show that for the same sample, each trace element abundance is small to one order of magnitude, and large to hundreds orders of magnitude, but for the different samples, the difference times of the same element abundance is ordinarily lower than one order of magnitude, some element(Ni and Ti)may reach up to one order of magnitude or more. In the same well field, the abundance distribution of part trace elements of samples from different wells present preferable regularity, such as Ni, Fe, Al, Cu, Ti, Mg, Cr and so on, and the distribution rules of Ni, Cu and Ti show a certain similarity, whereas the distribution of Cr, Al, Mn and Mg are similar to each other. As a whole, the distribution rule of main trace elements is that the abundance is increasing from downstructure location to structural high. Of all the samples, the ratios of V/Ni is generally low, range from 0.044 to 0.683, most of samples are less than 0.5, lower V/Ni ratio and high Fe content represent a strong reductive depositional environment. Variation characteristics of the single trace elements, such as Ni, Cu, Αl and Ti, obviously disappear a noticeable rule and indicated that oil migrated from Well Tazhong 69 and Well Tazhong 15 to Well Tazhong 16 and Well Tazhong 161, namely Silurian hydrocarbons in Tazhong area migrated towards structural high or stratigraphic pinch out direction, from northwest to southeast on the plane, which also reflected by the trace element suite. Therefore, trace elements of oilbearing fluid inclusion can provide effective evidence for studying oil and gas migratory direction.
2011, 29(5): 1002-1009.
Abstract:
Ordos basin is a large inner continental sedimentary basin in China, with an area of about 37×104 km2. It contains abundant Mesozoic crude oil resources with an reserve estimation of up to 10×108 metric tons of oil from Mesozoic reservoirs. These crude oils are derived nonmarine source rocks, so that it has also been used as a typical model of a nonmarine sedimentary basin generating oil. It contains six structural units. Stratigraphic sequences involving Mesozoic petroleum geology principally are Upper Triassic Yanchang Formation and Lower Jurassic Yanan Formation, which are both hydrocarbon source rocks and reservoirs of Mesozoic oils and gases in Ordos basin. Dongzhi Zhengning area is a new Mesozoic petroleum exploration target in the Ordos basin. Understanding the genesis of oil from this area is very important for revealing the formation law of oil reservoir and guiding petroleum exploration and development in this area. However, the research on geochemistry of crude oils from DongzhiZhengning area has been not performed and genesis of the oil is still known little. In this paper, biomarker compounds in oils from the region and Mesozoic source rock from Ordos basin were systematically analyzed. The genesis of the oil was discussed by studying the geochemical characteristics of these biomarker compounds. Similar geochemical features of oils from DongzhiZhengning area suggest generation from a source with mixed terrgenous and algalbacterial organic matter. The biomarker distributions of the oils show that they were formed under a weak reducing and freshwater environment. Molecular maturity parameters indicate that the crude oils are mature. The results of oilsource rock correlation showed that the oil was mainly derived from Chang7 source rock.
Ordos basin is a large inner continental sedimentary basin in China, with an area of about 37×104 km2. It contains abundant Mesozoic crude oil resources with an reserve estimation of up to 10×108 metric tons of oil from Mesozoic reservoirs. These crude oils are derived nonmarine source rocks, so that it has also been used as a typical model of a nonmarine sedimentary basin generating oil. It contains six structural units. Stratigraphic sequences involving Mesozoic petroleum geology principally are Upper Triassic Yanchang Formation and Lower Jurassic Yanan Formation, which are both hydrocarbon source rocks and reservoirs of Mesozoic oils and gases in Ordos basin. Dongzhi Zhengning area is a new Mesozoic petroleum exploration target in the Ordos basin. Understanding the genesis of oil from this area is very important for revealing the formation law of oil reservoir and guiding petroleum exploration and development in this area. However, the research on geochemistry of crude oils from DongzhiZhengning area has been not performed and genesis of the oil is still known little. In this paper, biomarker compounds in oils from the region and Mesozoic source rock from Ordos basin were systematically analyzed. The genesis of the oil was discussed by studying the geochemical characteristics of these biomarker compounds. Similar geochemical features of oils from DongzhiZhengning area suggest generation from a source with mixed terrgenous and algalbacterial organic matter. The biomarker distributions of the oils show that they were formed under a weak reducing and freshwater environment. Molecular maturity parameters indicate that the crude oils are mature. The results of oilsource rock correlation showed that the oil was mainly derived from Chang7 source rock.
2011, 29(5): 1010-1022.
Abstract:
By analyzing the data of the 137 dolomite reservoirs in the world with the C&C digital analogs knowledge system, the location of the oilfields, the structural setting, the type of basin, the depositional environment and the age of the dolomite strata were all investigated researched. The target is to find the relation between the production and these elements mentioned above. The geographical distribution of the dolomite fields are not evenly. Most of the dolomite fields were onshore oilfield, mainly distribute on the North America, Asia and Europe. The plate tectonics controlled these distribution: most of them have been discovered in compressional basins, especially in the suture belt, such as foreland basin and so on, but few dolomite fields can be found in the rift basin or the passive continental margin. The oil and gas accumulated in the Mesozoic and Paleozoic, mainly from the Cretaceous and Triassic. The next major development potential region are the lower Ordovician and the Cambrian. From the statistics analysis, the reservoirs are the sandy clastic current deposition in the low energy tidal flat lagoon environment and the turbidity current deposition from the foreslope to deepwater basin. The dolomitization and the cap rock can be formed likely in these conditions. If the carbonate platform margin reefs were dolomitized, its' porosity and permeability is not always enhanced. The high quality of the dolomite reservoirs maybe require the postcorrosion. The oilfields were discovered easily in the Sabkha sedimentary environment, but at the slope and the deepwater basin, the highenergy carbonate sand and the reefrimmed skeletal bank, the gas fields were found.The porosity and permeability of the dolomite reservoirs were gathered to indicate that high quality dolomite reservoirs were controlled by the dolomitization, the dissolution and the fracture density. The dolomitization and the dissolution provide the reservoir space and the fracture generated by the fracturing action can improve the permeable capacity of the reservoir. The main types of the reservoir structure are fracturepore, followed by the fracture and the main pore types are the intercrystalline pore,moldic pore and intergranular pore, followed by the fractures and caverns. The fracture action and the corrosion are the key point forming the high quality reservoirs.The sedimentary environment controlled the dolomitization and dissolution. The tectonic setting impact the degree of fracture development in the dolomite reservoir.The seal of the reservoirs were limited by the dolomitization environment composed by the marine shale and evaporates.
By analyzing the data of the 137 dolomite reservoirs in the world with the C&C digital analogs knowledge system, the location of the oilfields, the structural setting, the type of basin, the depositional environment and the age of the dolomite strata were all investigated researched. The target is to find the relation between the production and these elements mentioned above. The geographical distribution of the dolomite fields are not evenly. Most of the dolomite fields were onshore oilfield, mainly distribute on the North America, Asia and Europe. The plate tectonics controlled these distribution: most of them have been discovered in compressional basins, especially in the suture belt, such as foreland basin and so on, but few dolomite fields can be found in the rift basin or the passive continental margin. The oil and gas accumulated in the Mesozoic and Paleozoic, mainly from the Cretaceous and Triassic. The next major development potential region are the lower Ordovician and the Cambrian. From the statistics analysis, the reservoirs are the sandy clastic current deposition in the low energy tidal flat lagoon environment and the turbidity current deposition from the foreslope to deepwater basin. The dolomitization and the cap rock can be formed likely in these conditions. If the carbonate platform margin reefs were dolomitized, its' porosity and permeability is not always enhanced. The high quality of the dolomite reservoirs maybe require the postcorrosion. The oilfields were discovered easily in the Sabkha sedimentary environment, but at the slope and the deepwater basin, the highenergy carbonate sand and the reefrimmed skeletal bank, the gas fields were found.The porosity and permeability of the dolomite reservoirs were gathered to indicate that high quality dolomite reservoirs were controlled by the dolomitization, the dissolution and the fracture density. The dolomitization and the dissolution provide the reservoir space and the fracture generated by the fracturing action can improve the permeable capacity of the reservoir. The main types of the reservoir structure are fracturepore, followed by the fracture and the main pore types are the intercrystalline pore,moldic pore and intergranular pore, followed by the fractures and caverns. The fracture action and the corrosion are the key point forming the high quality reservoirs.The sedimentary environment controlled the dolomitization and dissolution. The tectonic setting impact the degree of fracture development in the dolomite reservoir.The seal of the reservoirs were limited by the dolomitization environment composed by the marine shale and evaporates.
2011, 29(5): 825-834.
Abstract:
In recent years, lots of new gas plays are found continuously in the Upper Paleozoic in southeast Ordos basin, which displays great exploration prospects. The Upper Paleozoic was influenced by multisource in the former study, while the main provenance was from north. It is not clear that whether there was sourthern provenance, how much the influenced area was, and what degree the influence was, which greatly influenced gas exploration strategy in the study area. Since lithologic play is the main reservoir in Ordos basin, the study on source and the rule of depositional facies on Upper Paleozoic sandbody distribution is of great importance in southeast Ordos basin. Based on data of well drilling, logging and core as long with outcrop sections of surroundings, by means of paleocurrent direction measuring in outcrop sections, heavy mineral analyzing as well as facies belt diagnosing, the provenance directions of the Permian are confined, the depositional facies styles of the Upper Paleozoic are analyzed, the rule of source, geography of depositional basement and depositional facies on sandbody distributions in the study area are studied, and also the distribution feature of skeleton sandbody are disclosured. Based on the above studies the following conclusion can be obtained. Paleocurrent direction revealed the whole middle part of the study area was catchment area in periods of Shanxi and Shehezi Formation, which suggests the possible existence of north and south of two different sources in the very time. Heavy mineral analyzing indicated that the NNE region of the studied area is rich in zircon, the NNW region of the studied area is mixed area of zircon, leucoxene and garnet, while the south region is rich in leucoxene, which disclosures that the provenance of Shanxi and Shehezi Formation can be divided into three directions which are NNE, NNW, and south. The coast line and geography of deposit basement reflected by thickness of strata and limestones indicated transgression direction being from east. Benxi Formation mainly developed barrier island & lagoon and tidal flat facies, the distribution of barrier island and tidal channel sandbodies were controlled by geography of deposit basement and depositional facies belts with the barrier sandbody being distributed along NNE direction. Depositional facies belts of Shanxi and Shehezi Formation were controlled by the orientation of provenance, which controlled the distribution of under water lobate distributary channels. Shan 2, Shan 1 and He 8 Member mainly developed delta front depositional facies sourced from different directions which were controlled by provenance directions and depositional facies belts, while Yan'an region being the center of water catchment. The skeleton sandbodies are composed of four under water lobate distributary channels converging to Yan'an region coming from NNE, NNE, and SSE as well as south direction, different sourced sandbodies in different layers display the style of overriding in water catchment area. The skeleton sandbodies sourced from south developed well in Shan2 member, which influenced areas of north of Yanan, while the skeleton sandbodies sourced from north developed well in He 8 member, which overreached areas of south of Yanan while the southern provenance receded simultaneously, reflecting that palaeoterrain in the studied area conversed from south being higher than north to north being higher than south, and also indicating that constitution reversed along NS direction in Ordos basin between periods of Shanxi and Shehezi Formation.
In recent years, lots of new gas plays are found continuously in the Upper Paleozoic in southeast Ordos basin, which displays great exploration prospects. The Upper Paleozoic was influenced by multisource in the former study, while the main provenance was from north. It is not clear that whether there was sourthern provenance, how much the influenced area was, and what degree the influence was, which greatly influenced gas exploration strategy in the study area. Since lithologic play is the main reservoir in Ordos basin, the study on source and the rule of depositional facies on Upper Paleozoic sandbody distribution is of great importance in southeast Ordos basin. Based on data of well drilling, logging and core as long with outcrop sections of surroundings, by means of paleocurrent direction measuring in outcrop sections, heavy mineral analyzing as well as facies belt diagnosing, the provenance directions of the Permian are confined, the depositional facies styles of the Upper Paleozoic are analyzed, the rule of source, geography of depositional basement and depositional facies on sandbody distributions in the study area are studied, and also the distribution feature of skeleton sandbody are disclosured. Based on the above studies the following conclusion can be obtained. Paleocurrent direction revealed the whole middle part of the study area was catchment area in periods of Shanxi and Shehezi Formation, which suggests the possible existence of north and south of two different sources in the very time. Heavy mineral analyzing indicated that the NNE region of the studied area is rich in zircon, the NNW region of the studied area is mixed area of zircon, leucoxene and garnet, while the south region is rich in leucoxene, which disclosures that the provenance of Shanxi and Shehezi Formation can be divided into three directions which are NNE, NNW, and south. The coast line and geography of deposit basement reflected by thickness of strata and limestones indicated transgression direction being from east. Benxi Formation mainly developed barrier island & lagoon and tidal flat facies, the distribution of barrier island and tidal channel sandbodies were controlled by geography of deposit basement and depositional facies belts with the barrier sandbody being distributed along NNE direction. Depositional facies belts of Shanxi and Shehezi Formation were controlled by the orientation of provenance, which controlled the distribution of under water lobate distributary channels. Shan 2, Shan 1 and He 8 Member mainly developed delta front depositional facies sourced from different directions which were controlled by provenance directions and depositional facies belts, while Yan'an region being the center of water catchment. The skeleton sandbodies are composed of four under water lobate distributary channels converging to Yan'an region coming from NNE, NNE, and SSE as well as south direction, different sourced sandbodies in different layers display the style of overriding in water catchment area. The skeleton sandbodies sourced from south developed well in Shan2 member, which influenced areas of north of Yanan, while the skeleton sandbodies sourced from north developed well in He 8 member, which overreached areas of south of Yanan while the southern provenance receded simultaneously, reflecting that palaeoterrain in the studied area conversed from south being higher than north to north being higher than south, and also indicating that constitution reversed along NS direction in Ordos basin between periods of Shanxi and Shehezi Formation.
2011, 29(5): 842-856.
Abstract:
Lower Ordovician dolomites in the central Tarim basin are of various types and extensively distributed. Seven dolostone types could be documented based on fabrics and structures, which are crystalline dolomite, residualgrain dolomite, residual calcite dolomite, algal dolomite,cloudy centers and clear rims dolomite, clitellum dolomite and gypes dolomite. It's characterised by middlehigh δ18O negative value（3.2%~8.7‰）, lowmiddle δ13C negative value（3%~0.77‰）, and high Z value of 118~123. Most diagenetic temperature calculated by empirical formulas using δ18O values are between 118 to 123℃, which indicates that the temperature degree of dolomitization is low, and so the kind of dolomite belongs to low temperature dolostone. These dolomites have also characteristics of low Mg/Ca and variable Fe/Mn ratio values. According to mineral composition analyzed by electron microprobe, dolomite monomineral can be divided into high Fe content and low Fe content species. 87Sr/86Sr ratios of most samples are low( among 0.708 8~0.709 7), which are similar to seawater strontium isotope composition, and some are of high ratios between 0.710 1 and 0.710 9. These characteristics reveal that the origin of dolomite in the study area can be classified into penecontemporaneous dolomitization and burial dolomitization. According to Ordovican palaeogeographical evolution, the penecontemporaneous dolomitization arised in the seafloor environment, mainly in tidal flats or beach environment. And this kind of dolomite characterised by low diagenetic temperature, low 87Sr/86Sr ratios, and low Fe content dolomite minerals. The burial dolomitization can be interpreted by two diagentic models. One is seepagereflux dolomitization during early shallow burial stage and characterised by low diagenetic temperature but high 87Sr/86Sr ratios, and high Fe content dolomite mineral. Another is deep burial dolomitization which occured in more strong reducible diagenetic enviornment during late deep burial stage. In general, the degree of dolomitization in burial diagentic enviorment is further enhanced and adjusted. The deep burial dolomite is characterised by high diagenetic temperature and high homogenization temperature of fluid inclusions, but low salinity.
Lower Ordovician dolomites in the central Tarim basin are of various types and extensively distributed. Seven dolostone types could be documented based on fabrics and structures, which are crystalline dolomite, residualgrain dolomite, residual calcite dolomite, algal dolomite,cloudy centers and clear rims dolomite, clitellum dolomite and gypes dolomite. It's characterised by middlehigh δ18O negative value（3.2%~8.7‰）, lowmiddle δ13C negative value（3%~0.77‰）, and high Z value of 118~123. Most diagenetic temperature calculated by empirical formulas using δ18O values are between 118 to 123℃, which indicates that the temperature degree of dolomitization is low, and so the kind of dolomite belongs to low temperature dolostone. These dolomites have also characteristics of low Mg/Ca and variable Fe/Mn ratio values. According to mineral composition analyzed by electron microprobe, dolomite monomineral can be divided into high Fe content and low Fe content species. 87Sr/86Sr ratios of most samples are low( among 0.708 8~0.709 7), which are similar to seawater strontium isotope composition, and some are of high ratios between 0.710 1 and 0.710 9. These characteristics reveal that the origin of dolomite in the study area can be classified into penecontemporaneous dolomitization and burial dolomitization. According to Ordovican palaeogeographical evolution, the penecontemporaneous dolomitization arised in the seafloor environment, mainly in tidal flats or beach environment. And this kind of dolomite characterised by low diagenetic temperature, low 87Sr/86Sr ratios, and low Fe content dolomite minerals. The burial dolomitization can be interpreted by two diagentic models. One is seepagereflux dolomitization during early shallow burial stage and characterised by low diagenetic temperature but high 87Sr/86Sr ratios, and high Fe content dolomite mineral. Another is deep burial dolomitization which occured in more strong reducible diagenetic enviornment during late deep burial stage. In general, the degree of dolomitization in burial diagentic enviorment is further enhanced and adjusted. The deep burial dolomite is characterised by high diagenetic temperature and high homogenization temperature of fluid inclusions, but low salinity.
2011, 29(5): 866-875.
Abstract:
Quantitative studies on the Paleogene sedimentary filling history and analysis of its controlling factors were carried out based on studies of topography, sediment provenance, constitution and distribution of sedimentary system in Qaidam basin. Western region of Qaidam basin can be divided into several secondary uplifts and depressions controlled by Cenozoic strikeslip process of Altyn Tagh. In Xiagancaigou depositional stage (about 60~40 Ma), with the fast uplift of Altyn Tagh, several subsidence centers were created in the front zone of Altyn Tagh. Deposition centers were transported from Shizigou to Nanyi mountain and Youquanzi area. It can be divided into two types of sedimentary areas during Xiagancaigou deposition period bounded by Jianding mountainNanyi mountainYouquanzi: (1) proximal deposits of alluvial fanfan deltasublacustrine fansemideep lake depositional systems at the front zone of Arkin mountain; (2) alluvial fanfluvialdeltashoreshallow lacustrine depositional systems at JiandingshanDafengshan ramp zone. Sedimentation of subsidence center at the front zone of Altyn mountain accelerated during Shanggancaigou deposition period, sedimentary facies in this period is mainly shallowlake facies. Affected by reduction of sediment supply by Niubiziliang, lake of Dafengshan region developed easternward and northwestern of Qaidam basin is extensively covered by shallow lacustrine.
Quantitative studies on the Paleogene sedimentary filling history and analysis of its controlling factors were carried out based on studies of topography, sediment provenance, constitution and distribution of sedimentary system in Qaidam basin. Western region of Qaidam basin can be divided into several secondary uplifts and depressions controlled by Cenozoic strikeslip process of Altyn Tagh. In Xiagancaigou depositional stage (about 60~40 Ma), with the fast uplift of Altyn Tagh, several subsidence centers were created in the front zone of Altyn Tagh. Deposition centers were transported from Shizigou to Nanyi mountain and Youquanzi area. It can be divided into two types of sedimentary areas during Xiagancaigou deposition period bounded by Jianding mountainNanyi mountainYouquanzi: (1) proximal deposits of alluvial fanfan deltasublacustrine fansemideep lake depositional systems at the front zone of Arkin mountain; (2) alluvial fanfluvialdeltashoreshallow lacustrine depositional systems at JiandingshanDafengshan ramp zone. Sedimentation of subsidence center at the front zone of Altyn mountain accelerated during Shanggancaigou deposition period, sedimentary facies in this period is mainly shallowlake facies. Affected by reduction of sediment supply by Niubiziliang, lake of Dafengshan region developed easternward and northwestern of Qaidam basin is extensively covered by shallow lacustrine.
2011, 29(5): 889-905.
Abstract:
The 4th member of Yingcheng Formation of lower Cretaceous is a series of stratigraphy of coarse clastic rock deposited in a background of volcano erupting of rift basin of Xujiaweizi faulted depression. It is the reservoir for natural gas pool. Using 3D seismic data of high resolution, cores, drilling logs and log curves, the framework of sequence stratigraphy and depositional systems of the 4th member were established by this paper based on sequence principle and the way of lithofacies analysis, respectively. Two thirdorder sequences were identified in the fourth member of Yingcheng Formation of lower Cretaceous in Xujiaweizi rifted depression. The sequence 1of lower fourth member (Sq1) of Yingcheng Formation was deposited in three geographically isolated volcano lakes formed by volcano erupting; the sequence 2 of the upper fourth member (Sq2) of Yingcheng Formation was deposited in a relative whole lake, because of the depression subsidence. Lakes during Sq1 period were well divided, in great disparity of depth, and mostly developed sedimentary systems of alluvial fan and fan delta being adjacent to the uplifts and characterized by lithofacies associations of cobble conglomerate and pebble conglomerate. Sq2 was formed in a relative whole lake, and developed a large scale sedimentary system of braided delta in the northern part of the depression and a sedimentary system of fluvial delta in the southern part of the depression. The two kinds of sedimentary system are characterized by lithofacies assemblages of pebble conglomerate, granular conglomerate, and coarse sandstone. The depositional system of braided delta is characterized by braided delta plain, composed of conglomerates, the thickness of which is great and the area of which is large. The depositional system of fluvial delta is characterized by proximal meandering river of conglomerate. Because of evolution of paleogeomorphology background from three small isolated lakes during Sq1 period to a relative whole lake in Sq2, depositional systems of alluvial fan and fan delta during Sq1 period changed to depositional system of braided river delta and depositional system of fluvial delta during Sq2 period. The front of delta is good reservoirs favorable for nature gas.
The 4th member of Yingcheng Formation of lower Cretaceous is a series of stratigraphy of coarse clastic rock deposited in a background of volcano erupting of rift basin of Xujiaweizi faulted depression. It is the reservoir for natural gas pool. Using 3D seismic data of high resolution, cores, drilling logs and log curves, the framework of sequence stratigraphy and depositional systems of the 4th member were established by this paper based on sequence principle and the way of lithofacies analysis, respectively. Two thirdorder sequences were identified in the fourth member of Yingcheng Formation of lower Cretaceous in Xujiaweizi rifted depression. The sequence 1of lower fourth member (Sq1) of Yingcheng Formation was deposited in three geographically isolated volcano lakes formed by volcano erupting; the sequence 2 of the upper fourth member (Sq2) of Yingcheng Formation was deposited in a relative whole lake, because of the depression subsidence. Lakes during Sq1 period were well divided, in great disparity of depth, and mostly developed sedimentary systems of alluvial fan and fan delta being adjacent to the uplifts and characterized by lithofacies associations of cobble conglomerate and pebble conglomerate. Sq2 was formed in a relative whole lake, and developed a large scale sedimentary system of braided delta in the northern part of the depression and a sedimentary system of fluvial delta in the southern part of the depression. The two kinds of sedimentary system are characterized by lithofacies assemblages of pebble conglomerate, granular conglomerate, and coarse sandstone. The depositional system of braided delta is characterized by braided delta plain, composed of conglomerates, the thickness of which is great and the area of which is large. The depositional system of fluvial delta is characterized by proximal meandering river of conglomerate. Because of evolution of paleogeomorphology background from three small isolated lakes during Sq1 period to a relative whole lake in Sq2, depositional systems of alluvial fan and fan delta during Sq1 period changed to depositional system of braided river delta and depositional system of fluvial delta during Sq2 period. The front of delta is good reservoirs favorable for nature gas.
2011, 29(5): 917-925.
Abstract:
Although predecessors have researched the sedimentation and sequence stratigraphy of Tabei area, the basin wide sequence stratigraphy is considered little. Using the theories and methods of sequence stratigraphy and modern sedimentology, emphasizing the overall research of the whole basin, we analyzed seismic data, logging and drilling core data of Triassic in Tarim Basin and identified the boundaries of sequences and system tracts. And five sequence boundaries with isochronous are developed and four thirdorder sequences are divided. According to division of internal structure,a unified sequence stratigraphic framework between well and seismic is established in platform area. Affected by tectonic activity and other factors,the characteristics of lateral distribution and internal structure in each sequence are different. SQ1 and SQ2 gradually overlap to the southern slope of Tabei uplift, SQ4 is suffered extensive uplift and erosion in Tazhong area, the distribution of each sequence is more stable in the inner basin. Braided delta and lake is the main sedimentary facies,which represents the deposition of broadshallow depression lake basin. As the main sedimentation type, braided delta is located in the slope area of Tazhong and Tabei, lake is deposited in the central basin. The favorable reservoir sand is formed by braided channel, underwater distributary channel, channel mouth bar and longshore bar. The identification of sequence boundaries and stratigraphic framework will improve the accuracy of reservoir prediction and provide foundation for integral deployment of petroleum exploration.
Although predecessors have researched the sedimentation and sequence stratigraphy of Tabei area, the basin wide sequence stratigraphy is considered little. Using the theories and methods of sequence stratigraphy and modern sedimentology, emphasizing the overall research of the whole basin, we analyzed seismic data, logging and drilling core data of Triassic in Tarim Basin and identified the boundaries of sequences and system tracts. And five sequence boundaries with isochronous are developed and four thirdorder sequences are divided. According to division of internal structure,a unified sequence stratigraphic framework between well and seismic is established in platform area. Affected by tectonic activity and other factors,the characteristics of lateral distribution and internal structure in each sequence are different. SQ1 and SQ2 gradually overlap to the southern slope of Tabei uplift, SQ4 is suffered extensive uplift and erosion in Tazhong area, the distribution of each sequence is more stable in the inner basin. Braided delta and lake is the main sedimentary facies,which represents the deposition of broadshallow depression lake basin. As the main sedimentation type, braided delta is located in the slope area of Tazhong and Tabei, lake is deposited in the central basin. The favorable reservoir sand is formed by braided channel, underwater distributary channel, channel mouth bar and longshore bar. The identification of sequence boundaries and stratigraphic framework will improve the accuracy of reservoir prediction and provide foundation for integral deployment of petroleum exploration.
2011, 29(5): 935-945.
Abstract:
The diamicton of Jinpingzi, which looks like a slide according to morphological character, lies on the Kangdian tectonic zone. It is a composite diamicton that formed due to several dynamic actions at the different periods, and is a product of three geomorphic systems i.e. the ancient Jinsha river, the old Jinsha river and the modern Jinsha river ,which occurred alternately.
According to the DEM of the diamicton of Jinpingzi and the field investigation, there are eight geomorphic units in the diamicton of Jinpingzi, which are the upside slope, the debris flow fan, the accumulational flatform on palaeogully of Jinpingzi, the valley slide of the Jinsha river, the terrace of the Jinsha river, the beach face composed of boulders and rock masses, the meander core and the Xiaogou gully. The TL age of the terrace in the surface of the diamicton of Jinpingzi is (41.13 3.49)kaB.P..
The multidisciplinary study (sedimentology,chronology, lithostratigraphy) of the sediment of the dill of the landform suggests that the diamicton of Jinpingzi is composed of twelve stratums. The stratums form the first to the ninth are composed of colluviums, alluviums and slope wash, while the others are composed of debris flow.
According to geomorphologic and sedimentologic characters of the diamicton of Jinpingzi, we can conclude that there are three geomorphologic processes, which are accumulation and sidesway(197~137 kaB.P.), divagation and incision(137~41kaB.P.) and intensity incision(41~0 kaB.P.). Finally the meander core formed after the deeplyincising of Jinsha river, and the cliff of the breccia formed.
The diamicton of Jinpingzi, which looks like a slide according to morphological character, lies on the Kangdian tectonic zone. It is a composite diamicton that formed due to several dynamic actions at the different periods, and is a product of three geomorphic systems i.e. the ancient Jinsha river, the old Jinsha river and the modern Jinsha river ,which occurred alternately.
According to the DEM of the diamicton of Jinpingzi and the field investigation, there are eight geomorphic units in the diamicton of Jinpingzi, which are the upside slope, the debris flow fan, the accumulational flatform on palaeogully of Jinpingzi, the valley slide of the Jinsha river, the terrace of the Jinsha river, the beach face composed of boulders and rock masses, the meander core and the Xiaogou gully. The TL age of the terrace in the surface of the diamicton of Jinpingzi is (41.13 3.49)kaB.P..
The multidisciplinary study (sedimentology,chronology, lithostratigraphy) of the sediment of the dill of the landform suggests that the diamicton of Jinpingzi is composed of twelve stratums. The stratums form the first to the ninth are composed of colluviums, alluviums and slope wash, while the others are composed of debris flow.
According to geomorphologic and sedimentologic characters of the diamicton of Jinpingzi, we can conclude that there are three geomorphologic processes, which are accumulation and sidesway(197~137 kaB.P.), divagation and incision(137~41kaB.P.) and intensity incision(41~0 kaB.P.). Finally the meander core formed after the deeplyincising of Jinsha river, and the cliff of the breccia formed.
2011, 29(5): 962-969.
Abstract:
Nowadays, we have a common consideration that the PreJurassic palaeogeomorphology is the important basis which control the Yan9Yan10's reservoirs of the lower part of the Yan'an Group. Before, for the lower quality of seismic data and less wells' data, we recovered the palaeogeomorphology from the aspects of terrain's height, slopes and valleys, however, when the reservoirs were on the development stage, the aforementioned palaeogeomorphic characterization was too macro, especially, it was too simple and coarse for the palaeogeomorphic positive landscape, which resulted in a difficulty to master the distribution law of the PreJurassic reservoirs, and restricted the Jurassic reservoirs' exploration and development, thus, it was urgently to have a fine palaeogeomorphic characterization for the PreJurassic.
Under the conditions of the increasing exploration data and higher quality data, the requirements of finely characterization the PreJurassic palaeogeomorphology has achieved. According to the formation marks of the Yan8, Yan9, Yan10 of the lower Jurassic and Fuxian group in Shangliyuan area, eastern Gansu Province, recognized and correlated the lower Jurassic and Fuxian Formations, based on the characteristics of the later Triassic structure movement and early Jurassic deposition environment, we used the stratum thickness impression method (Yan9 add Yan10 and add Fuxian formations' thickness) to rebuild the preJurassic palaeogeomorphology of Shangliyuan area, eastern Gansu Province. There were six landscape types: valleys, slopes, highlands, remnant ridges and remnant earthen mounds of the palaeogeomorphology, the specific configuration was the first degree GanShan ancient river distributed from west to east, and the second Western Qing ancient river laid in south of the study area and flowed northwards into GanShan ancient river, the Jiyuan and Yanwu high lands, respectively, located in the north and south of the study area, the Jiyuan south slope and Yanwu north slope developed in the transitional zone between the high lands and the valley, furthermore, there were interriver mounds in the center of the first degree ancient valley and there were second landforms of remnant mounds and ridges in the slope.
On the above basis, we put for ward an oil accumulation palaeogeomorphology conceptions, that was, the palaeogeomorphology could control and organically combine the reservoirs' accumulation elements, and made it form an organic reservoirs' deployment conditions, eventually, had a crucial affection on reservoirs' accumulation. The results showed that three types' reservoirs "remnant ridges, remnant earthen mounds and interriver mounds" occupied 80% in all the Lower Jurassic reservoirs in Shangliyuan area, eastern Gansu Province, associated with the distribution characteristic and formed law of the Lower Jurassic reservoirs, we considered the remnant ridges, remnant earthen mounds and interriver mounds were the main oil accumulation ancient landscapes. On the principle of "the present is the key to the past", we studied the characteristics of modern erosion landscapes and analyzed their genetic models, then divided the three main oil accumulation landscapes to three genetic models: river robber, river transformation and watershed erosion. The oil accumulation ancient landscapes made the reservoirs' formed models were led by structure and controlled by lithology, and the advantageous reservoirs' formed conditions of the oil accumulation ancient landscapes to the Lower Jurassic reservoirs was: ① differential compaction small amplitude anticline and cove structure came from rigid oil accumulation palaeogeomorphology with its upper Yan’an group “soft stratum”; ② the oil accumulation palaeogeomorphology easily to form river sandstone division and drape sandstone capes, then formed isolated lens reservoir sandstone.
We applied the oil accumulation palaeogeomorphology conceptions to divide the oil accumulation palaeogeomorphology types of the PreJurassic in Shangliyuan area, eastern Gansu Province, and discussed the their geneses and analyzed the favorable reservoirs' formed conditions, the purpose was to suggest a theory foundation and technical support on the exploration and development for the Lower Jurassic reservoirs in Ordos basin, meanwhile, provided studying ideas and methods for palaeogeomorphology reservoirs, and enrichment and supplement to the research theory of these reservoirs' types.
Nowadays, we have a common consideration that the PreJurassic palaeogeomorphology is the important basis which control the Yan9Yan10's reservoirs of the lower part of the Yan'an Group. Before, for the lower quality of seismic data and less wells' data, we recovered the palaeogeomorphology from the aspects of terrain's height, slopes and valleys, however, when the reservoirs were on the development stage, the aforementioned palaeogeomorphic characterization was too macro, especially, it was too simple and coarse for the palaeogeomorphic positive landscape, which resulted in a difficulty to master the distribution law of the PreJurassic reservoirs, and restricted the Jurassic reservoirs' exploration and development, thus, it was urgently to have a fine palaeogeomorphic characterization for the PreJurassic.
Under the conditions of the increasing exploration data and higher quality data, the requirements of finely characterization the PreJurassic palaeogeomorphology has achieved. According to the formation marks of the Yan8, Yan9, Yan10 of the lower Jurassic and Fuxian group in Shangliyuan area, eastern Gansu Province, recognized and correlated the lower Jurassic and Fuxian Formations, based on the characteristics of the later Triassic structure movement and early Jurassic deposition environment, we used the stratum thickness impression method (Yan9 add Yan10 and add Fuxian formations' thickness) to rebuild the preJurassic palaeogeomorphology of Shangliyuan area, eastern Gansu Province. There were six landscape types: valleys, slopes, highlands, remnant ridges and remnant earthen mounds of the palaeogeomorphology, the specific configuration was the first degree GanShan ancient river distributed from west to east, and the second Western Qing ancient river laid in south of the study area and flowed northwards into GanShan ancient river, the Jiyuan and Yanwu high lands, respectively, located in the north and south of the study area, the Jiyuan south slope and Yanwu north slope developed in the transitional zone between the high lands and the valley, furthermore, there were interriver mounds in the center of the first degree ancient valley and there were second landforms of remnant mounds and ridges in the slope.
On the above basis, we put for ward an oil accumulation palaeogeomorphology conceptions, that was, the palaeogeomorphology could control and organically combine the reservoirs' accumulation elements, and made it form an organic reservoirs' deployment conditions, eventually, had a crucial affection on reservoirs' accumulation. The results showed that three types' reservoirs "remnant ridges, remnant earthen mounds and interriver mounds" occupied 80% in all the Lower Jurassic reservoirs in Shangliyuan area, eastern Gansu Province, associated with the distribution characteristic and formed law of the Lower Jurassic reservoirs, we considered the remnant ridges, remnant earthen mounds and interriver mounds were the main oil accumulation ancient landscapes. On the principle of "the present is the key to the past", we studied the characteristics of modern erosion landscapes and analyzed their genetic models, then divided the three main oil accumulation landscapes to three genetic models: river robber, river transformation and watershed erosion. The oil accumulation ancient landscapes made the reservoirs' formed models were led by structure and controlled by lithology, and the advantageous reservoirs' formed conditions of the oil accumulation ancient landscapes to the Lower Jurassic reservoirs was: ① differential compaction small amplitude anticline and cove structure came from rigid oil accumulation palaeogeomorphology with its upper Yan’an group “soft stratum”; ② the oil accumulation palaeogeomorphology easily to form river sandstone division and drape sandstone capes, then formed isolated lens reservoir sandstone.
We applied the oil accumulation palaeogeomorphology conceptions to divide the oil accumulation palaeogeomorphology types of the PreJurassic in Shangliyuan area, eastern Gansu Province, and discussed the their geneses and analyzed the favorable reservoirs' formed conditions, the purpose was to suggest a theory foundation and technical support on the exploration and development for the Lower Jurassic reservoirs in Ordos basin, meanwhile, provided studying ideas and methods for palaeogeomorphology reservoirs, and enrichment and supplement to the research theory of these reservoirs' types.
2011, 29(5): 980-985.
Abstract:
Jixi basin is the MesozoicCenozoic residue basin and the important coal base in the northeast China. At present, several drilling wells in the coal fields discovered the oil and gas shows in this area. Chengzihe Formation is the coalbearing formation in the lower Cretaceous of the Jixi basin, which deposited in the circumstance of coastalshallow lake. The previous studies found the mussels fossil of brackish water and a lot of dinoflagellates of marine facies, which reflected the marine interlayer existed in the Chengzihe Formation. It infers that the transgression occurred in this period. At home and abroad, many studies indicate that the main source rock layers in the majority of oil and gas bearing basin are related closely with the transgression. We choose some mud rocks from the Chengzihe Formation and perform analysis on the major element and trace element, combining with the previous organic geochemistry data, to reveal the character of water circumstance when the mud rock of Chengzihe Formation deposits, and discuss how the transgression influences on the water circumstance and organic matter preservation. The analysis result indicates that the values of Sr/Ba which is salinity index ranging from 0.11 to 0.38, 0.26 average; the (Ca+Mg)*20/(Si+Al), as the alkalinity index, is from 0.22 to 1.33, 1.68 average; as the oxidationreduction indexes, V/Cr is 1.17~3.23, and Ni/Co is 0.89~3.71. Compared with the typical transgression sequence from Quantou Formation to Nenjiang Formation in Songliao basin, the values are low obviously in the Chengzihe Formation, which reflects the sediment and preservation circumstances of low salinity, low alkalinity and weak oxidation. In recent years, the analysis results on the biomarkers from the Chengzihe Formation indicate that as the oxidationreduction index, the value of Pr/Ph is 2.4~2.8, 2.2 average; the G/C30H which indicates the salinity stratification of water column is 0.11 average; the pregnane+homopregnane / C27sterane is 0.88 average, C27diasterane/C27sterane is 0.34 average, reflecting the salinity of water is low, which is coincide with the analytical result of the major element and trace element. All kinds of indexes do not show the character of the typical transgression sequence, such as the high salinity water and the strong reducive sediment circumstance. It indicates that the sediment environment is not fit for the organic matter preservation. It is coincident with the Gaofuhong(2007)'study on the typical transgression sequence of Yuliangzigou section in the Chengzihe Formation.
In addition, the previous study on the potential of generating hydrocarbon reveals the TOC value of the black mud rock is between 0.11% and 3.87, which is lower than the value of the coal and the carbonaceous mud rock, the TOC of which ranges from 18.58% to 80.27%. Besides, the hydrogen index (HI) of the black mud stone is 0.02~144.00 mg/g, and the generating hydrocarbon potential (S1+S2) is between 0.04~4.16 mg/g, all of which is lower than the value of the coal and the carbonaceous mud rock that the IH is 53.8 mg/g~207 mg/g, and the S1+S2 is 16.93~179.99 mg/g. The organic matter type (ⅡB )of the coal and carbonaceous muddy rock is better than the organic matter type(Ⅲ) of the black mud rock. It indicates that the coal and carbonaceous mud rock have the advantageous potential of generating hydrocarbon.
Some evidence of sedimenary facies study indicate that the water area reached the maximum during the whole periods in this basin, and it is probably that the Jixi basin, Boli basin in the north and the Hulin basin in the northeast form the uniform basin, suffering the transgression from the east. However, a lot of coal in Chengzihe Formation of Jixi basin and the geochemical evidence from the previous and present studies indicate that the transgression do not improve sediment environment evidently. Contrasting with Songliao basin, the scale of transgression is smaller in the Jixi basin, which do not improve the salinity and alkalinity evidently, so the water environment of the Chengzihe Formation is not good for the organic matter preservation. Due to the advantageous generating hydrocarbon potential of the coal and carbonaceous mud rock, it infers the oil and gas show in this area is probably related to the coal and carbonate mud rock.
Jixi basin is the MesozoicCenozoic residue basin and the important coal base in the northeast China. At present, several drilling wells in the coal fields discovered the oil and gas shows in this area. Chengzihe Formation is the coalbearing formation in the lower Cretaceous of the Jixi basin, which deposited in the circumstance of coastalshallow lake. The previous studies found the mussels fossil of brackish water and a lot of dinoflagellates of marine facies, which reflected the marine interlayer existed in the Chengzihe Formation. It infers that the transgression occurred in this period. At home and abroad, many studies indicate that the main source rock layers in the majority of oil and gas bearing basin are related closely with the transgression. We choose some mud rocks from the Chengzihe Formation and perform analysis on the major element and trace element, combining with the previous organic geochemistry data, to reveal the character of water circumstance when the mud rock of Chengzihe Formation deposits, and discuss how the transgression influences on the water circumstance and organic matter preservation. The analysis result indicates that the values of Sr/Ba which is salinity index ranging from 0.11 to 0.38, 0.26 average; the (Ca+Mg)*20/(Si+Al), as the alkalinity index, is from 0.22 to 1.33, 1.68 average; as the oxidationreduction indexes, V/Cr is 1.17~3.23, and Ni/Co is 0.89~3.71. Compared with the typical transgression sequence from Quantou Formation to Nenjiang Formation in Songliao basin, the values are low obviously in the Chengzihe Formation, which reflects the sediment and preservation circumstances of low salinity, low alkalinity and weak oxidation. In recent years, the analysis results on the biomarkers from the Chengzihe Formation indicate that as the oxidationreduction index, the value of Pr/Ph is 2.4~2.8, 2.2 average; the G/C30H which indicates the salinity stratification of water column is 0.11 average; the pregnane+homopregnane / C27sterane is 0.88 average, C27diasterane/C27sterane is 0.34 average, reflecting the salinity of water is low, which is coincide with the analytical result of the major element and trace element. All kinds of indexes do not show the character of the typical transgression sequence, such as the high salinity water and the strong reducive sediment circumstance. It indicates that the sediment environment is not fit for the organic matter preservation. It is coincident with the Gaofuhong(2007)'study on the typical transgression sequence of Yuliangzigou section in the Chengzihe Formation.
In addition, the previous study on the potential of generating hydrocarbon reveals the TOC value of the black mud rock is between 0.11% and 3.87, which is lower than the value of the coal and the carbonaceous mud rock, the TOC of which ranges from 18.58% to 80.27%. Besides, the hydrogen index (HI) of the black mud stone is 0.02~144.00 mg/g, and the generating hydrocarbon potential (S1+S2) is between 0.04~4.16 mg/g, all of which is lower than the value of the coal and the carbonaceous mud rock that the IH is 53.8 mg/g~207 mg/g, and the S1+S2 is 16.93~179.99 mg/g. The organic matter type (ⅡB )of the coal and carbonaceous muddy rock is better than the organic matter type(Ⅲ) of the black mud rock. It indicates that the coal and carbonaceous mud rock have the advantageous potential of generating hydrocarbon.
Some evidence of sedimenary facies study indicate that the water area reached the maximum during the whole periods in this basin, and it is probably that the Jixi basin, Boli basin in the north and the Hulin basin in the northeast form the uniform basin, suffering the transgression from the east. However, a lot of coal in Chengzihe Formation of Jixi basin and the geochemical evidence from the previous and present studies indicate that the transgression do not improve sediment environment evidently. Contrasting with Songliao basin, the scale of transgression is smaller in the Jixi basin, which do not improve the salinity and alkalinity evidently, so the water environment of the Chengzihe Formation is not good for the organic matter preservation. Due to the advantageous generating hydrocarbon potential of the coal and carbonaceous mud rock, it infers the oil and gas show in this area is probably related to the coal and carbonate mud rock.
2011, 29(5): 994-1001.
Abstract:
In the system of crude oil and magnesium sulfate, thermal sulfate reduction was conducted in autoclave under certain temperature and pressure conditions. The thermalsimulation experiments were performed at 350~450℃ in the presence of water.
Gaseous products were analyzed using gas chromatography and microcoulometry. Gaseous products were composed of saturated hydrocarbons (C1 ~ C6), unsaturated hydrocarbons (C2~C5) and H2, CO2, CO. Content of CH4, H2 and CO2 increased with temperature growing. Gas dryness coefficient which was used to monitor the evolution of the hydrocarbon gas population also increased with temperature growing. Gas dryness coefficient of TSR was much more than Gas dryness coefficient of crude oil pyrolysis. It showed that the capacity of sulfate oxidization hydrocarbon increased with temperature growing.
Total sulfate of the liquid products was analyzed by microcoulometry. At the begining, content of total sulfur in liquid products of TSR was higher than crude oil. It implied the reaction temperature for the system of crude oil and magnesium sulfate was lower than the pyrolysis temperature of crude oil. With the temperature growing, content of total sulfur in liquid products of reaction of Tuha crude oil and magnesium sulfate gradually reduced. It may be that large amounts of Labile Sulfur Compounds (LSC) contains in Tuha crude oil, whose degradation rate was higher than generation rate during reaction. While content of total sulfur in liquid products of reaction of Shengli crude oil and magnesium sulfate increaseed and then sharply reduced. It may be a lot of Stable Sulfur Compounds (SSC) contained in Shengli crude oil, which was hard to degrade in lower temperature.
Solid products were analyzed by FTIR and Xray diffraction. MgO and MgSO4 were found to coexist in solid product of TSR. According to the the molar conversion calculated from the weight change of the solid products, the reaction kinetics was investigated. The activation energy of the system of Tuha crude oil and magnesium sulfate was 53.26 kJ/mol, while activation energy of Shengli crude oil and magnesium sulfate was 57.91 kJ/mol. Relative to the geological condition, the activation energy of crude oil and magnesium sulfate was lower. It was likely to be that the temperature of simulation experiment was higher than the critical temperature of water. Supercritical water could reduce the energy required to generate free radicals, which resulted in the faster reaction rate.
The activation energy of the system of Tuha crude oil and magnesium sulfate was higher than activation energy of Shengli crude oil and magnesium sulfate.This maybe relate with content of LSC. It showed that content of LSC in the crude oil effected on the extent of reaction. The higher content of LSC, the stronger activity of TSR. In addition, the LSC has certain effect on the initial temperature of the TSR. LSC leaded to form reactive intermediates sulfate ester in the process of TSR. Sulfate esters were relatively unstable and would be expected to oxidize the hydrocarbon. This mechanism provided a possible explanation on the role of LSC in enhancing the rate of TSR at the initial stages.
In the system of crude oil and magnesium sulfate, thermal sulfate reduction was conducted in autoclave under certain temperature and pressure conditions. The thermalsimulation experiments were performed at 350~450℃ in the presence of water.
Gaseous products were analyzed using gas chromatography and microcoulometry. Gaseous products were composed of saturated hydrocarbons (C1 ~ C6), unsaturated hydrocarbons (C2~C5) and H2, CO2, CO. Content of CH4, H2 and CO2 increased with temperature growing. Gas dryness coefficient which was used to monitor the evolution of the hydrocarbon gas population also increased with temperature growing. Gas dryness coefficient of TSR was much more than Gas dryness coefficient of crude oil pyrolysis. It showed that the capacity of sulfate oxidization hydrocarbon increased with temperature growing.
Total sulfate of the liquid products was analyzed by microcoulometry. At the begining, content of total sulfur in liquid products of TSR was higher than crude oil. It implied the reaction temperature for the system of crude oil and magnesium sulfate was lower than the pyrolysis temperature of crude oil. With the temperature growing, content of total sulfur in liquid products of reaction of Tuha crude oil and magnesium sulfate gradually reduced. It may be that large amounts of Labile Sulfur Compounds (LSC) contains in Tuha crude oil, whose degradation rate was higher than generation rate during reaction. While content of total sulfur in liquid products of reaction of Shengli crude oil and magnesium sulfate increaseed and then sharply reduced. It may be a lot of Stable Sulfur Compounds (SSC) contained in Shengli crude oil, which was hard to degrade in lower temperature.
Solid products were analyzed by FTIR and Xray diffraction. MgO and MgSO4 were found to coexist in solid product of TSR. According to the the molar conversion calculated from the weight change of the solid products, the reaction kinetics was investigated. The activation energy of the system of Tuha crude oil and magnesium sulfate was 53.26 kJ/mol, while activation energy of Shengli crude oil and magnesium sulfate was 57.91 kJ/mol. Relative to the geological condition, the activation energy of crude oil and magnesium sulfate was lower. It was likely to be that the temperature of simulation experiment was higher than the critical temperature of water. Supercritical water could reduce the energy required to generate free radicals, which resulted in the faster reaction rate.
The activation energy of the system of Tuha crude oil and magnesium sulfate was higher than activation energy of Shengli crude oil and magnesium sulfate.This maybe relate with content of LSC. It showed that content of LSC in the crude oil effected on the extent of reaction. The higher content of LSC, the stronger activity of TSR. In addition, the LSC has certain effect on the initial temperature of the TSR. LSC leaded to form reactive intermediates sulfate ester in the process of TSR. Sulfate esters were relatively unstable and would be expected to oxidize the hydrocarbon. This mechanism provided a possible explanation on the role of LSC in enhancing the rate of TSR at the initial stages.
