2006 Vol. 24, No. 1
Display Method:
2006, 24(1): 1-9.
Abstract:
There are extrathick high quality coal for liquidation oil in the Xianfeng basin, Yunnan Province, China. There are abundant sedimentary marks of allochthonous genesis in the extrathick coalbeds. These genetic indicators reveal two new submodels about allochthonous accumulation: that is, "the river distant transport of plant detritus→the sedimention of plant detritus fan delta or plant detritus delta + the allochthonous sedimention of lacustrine drift plant detritus + the hypautochthony accumulation of local lakeshore swamp peat + the autochthonous accumulation of local lacustrine algae peat + the sedimention fine detritus→the mix and transport because of flood current or weak storm flow or underwater gravity flow→the mechanical differentiation and resedimentation of plant detritus and inorganic detritus’, can be recapitulated. It can be deduced to the twice accumulation of lacustrine plant detritus fan delta and underwater gravity flow’or be reduced to Xianfeng submodel’. This submodel supplements the allochthonoushypautochthony lacustrine combination accumulation model’ of the extrathick coalbeds of Fuxin submodel and Fushun submodel in Chinese Mesozoic and Cenozoic intracontinental fault basin.
There are extrathick high quality coal for liquidation oil in the Xianfeng basin, Yunnan Province, China. There are abundant sedimentary marks of allochthonous genesis in the extrathick coalbeds. These genetic indicators reveal two new submodels about allochthonous accumulation: that is, "the river distant transport of plant detritus→the sedimention of plant detritus fan delta or plant detritus delta + the allochthonous sedimention of lacustrine drift plant detritus + the hypautochthony accumulation of local lakeshore swamp peat + the autochthonous accumulation of local lacustrine algae peat + the sedimention fine detritus→the mix and transport because of flood current or weak storm flow or underwater gravity flow→the mechanical differentiation and resedimentation of plant detritus and inorganic detritus’, can be recapitulated. It can be deduced to the twice accumulation of lacustrine plant detritus fan delta and underwater gravity flow’or be reduced to Xianfeng submodel’. This submodel supplements the allochthonoushypautochthony lacustrine combination accumulation model’ of the extrathick coalbeds of Fuxin submodel and Fushun submodel in Chinese Mesozoic and Cenozoic intracontinental fault basin.
2006, 24(1): 19-27.
Abstract:
Tarim basin underwent the ramp carbonate platform of earlymiddle Cambrian, rimmed shelf carbonate platform of late Cambrianearly middle Ordovician, isolated carbonate platform in the early period of late Ordovician, and drowned carbonate platform in the middlelate period of late Ordovician. The different carbonate platform has distinct diversities in the section structure, platform edge feature and facies constitution, and controls the types and features of facies in the different regions and the upgrowth condition and the distribution rule of source rock, reservoir and caps. Through the sequence stratigraphy study of the seismic and loggings, 4 types of carbonate platform structure have been established and 5 sequencefacies models been summarized. During carbonate platform evolvement, two periods of platform slope are developed: The first platform slope is formed in Cambrianearly middle Ordovician, controlled by Well Kunan 1, WellMancan 1, WellTadong 2 route, represents arc belt toward the west. The second platform slope is formed in the late Ordovician, constrained by Well Kunan 1, WellMancan 1, WellTazhong 1 and WellTangcan 1, represents arc belt toward the east. The shifting and variation of the slope reveals the change of carbonate platform types.
Tarim basin underwent the ramp carbonate platform of earlymiddle Cambrian, rimmed shelf carbonate platform of late Cambrianearly middle Ordovician, isolated carbonate platform in the early period of late Ordovician, and drowned carbonate platform in the middlelate period of late Ordovician. The different carbonate platform has distinct diversities in the section structure, platform edge feature and facies constitution, and controls the types and features of facies in the different regions and the upgrowth condition and the distribution rule of source rock, reservoir and caps. Through the sequence stratigraphy study of the seismic and loggings, 4 types of carbonate platform structure have been established and 5 sequencefacies models been summarized. During carbonate platform evolvement, two periods of platform slope are developed: The first platform slope is formed in Cambrianearly middle Ordovician, controlled by Well Kunan 1, WellMancan 1, WellTadong 2 route, represents arc belt toward the west. The second platform slope is formed in the late Ordovician, constrained by Well Kunan 1, WellMancan 1, WellTazhong 1 and WellTangcan 1, represents arc belt toward the east. The shifting and variation of the slope reveals the change of carbonate platform types.
2006, 24(1): 36-42.
Abstract:
Tabamiao area of Ordos basin from Taiyuan Formation in Upper Carboniferous to Shanxi Formation in Lower Permian underwent a prograding sedimentary evolution process, i.e. from tidal flat to lagoon marinecontinental transition delta. Previous studies drew different conclusions after studying the depositional environmental of member 1 of Shanxi Formation during the evolution. Some think it was the lake delta of the terrestrial facies, others believe that it was the deposition of marinecontinental transition delta,or the lake delta but influenced by the intermittent transgression. This paper, based on previous data, detailed core observation and petrology features, puts forward that member 1 of Shanxi Formation represents marine facies or the marinecontinental transition depositional environment, such as ①high maturity of the component and texture squartz-sandstone, ②micrite siderite stone, ③sea lily, foraminifer mudstone，④bauxite mudstone and ⑤crystal powder dolomite. Those marine facies depositional environmental features prove the depositional process of Tabamiao area member 1 of Shanxi formation is marine facies or marinecontinental transition depositional environment. Authors also discussed the spatialtemporal evolution characteristics of member 1 of Shanxi Formation depositional environment.
Tabamiao area of Ordos basin from Taiyuan Formation in Upper Carboniferous to Shanxi Formation in Lower Permian underwent a prograding sedimentary evolution process, i.e. from tidal flat to lagoon marinecontinental transition delta. Previous studies drew different conclusions after studying the depositional environmental of member 1 of Shanxi Formation during the evolution. Some think it was the lake delta of the terrestrial facies, others believe that it was the deposition of marinecontinental transition delta,or the lake delta but influenced by the intermittent transgression. This paper, based on previous data, detailed core observation and petrology features, puts forward that member 1 of Shanxi Formation represents marine facies or the marinecontinental transition depositional environment, such as ①high maturity of the component and texture squartz-sandstone, ②micrite siderite stone, ③sea lily, foraminifer mudstone，④bauxite mudstone and ⑤crystal powder dolomite. Those marine facies depositional environmental features prove the depositional process of Tabamiao area member 1 of Shanxi formation is marine facies or marinecontinental transition depositional environment. Authors also discussed the spatialtemporal evolution characteristics of member 1 of Shanxi Formation depositional environment.
2006, 24(1): 50-55.
Abstract:
The fluxoturbidite in front of delta is an important kind of lithologic hydrocarbon reservoirs in fault basins. According to interior flume experiment simulations, the formation of fluxoturbidite in front of delta is studied under different conditions. The laboratory findings show that trigger mechanisms are the precondition to form turbidite, which include external mechanisms such as seismicity and wave action and internal mechanism such as compaction and depression of deltafront sands under gravity. Seismicity can damage the stability of delta front and form liquefied fluxoturbidite and faulted fluxoturbidite. The sediments of delta front around wave base plane are eroded by wave action and took along to redeposit below wave base plane, during which turbidite is formed. Without external mechanisms the sands in inlet of main stem can compact and descent to underneath mudstone and form fluxoturbidite. The driving force of fluxoturbidite to migrate mainly is the gravity of slumping sands. Moreover, the collisionpower from hinder overlapped sand body is also the motility of faulted fluxoturbidite to move more distant besides its own gravity.
〖WTHZ
The fluxoturbidite in front of delta is an important kind of lithologic hydrocarbon reservoirs in fault basins. According to interior flume experiment simulations, the formation of fluxoturbidite in front of delta is studied under different conditions. The laboratory findings show that trigger mechanisms are the precondition to form turbidite, which include external mechanisms such as seismicity and wave action and internal mechanism such as compaction and depression of deltafront sands under gravity. Seismicity can damage the stability of delta front and form liquefied fluxoturbidite and faulted fluxoturbidite. The sediments of delta front around wave base plane are eroded by wave action and took along to redeposit below wave base plane, during which turbidite is formed. Without external mechanisms the sands in inlet of main stem can compact and descent to underneath mudstone and form fluxoturbidite. The driving force of fluxoturbidite to migrate mainly is the gravity of slumping sands. Moreover, the collisionpower from hinder overlapped sand body is also the motility of faulted fluxoturbidite to move more distant besides its own gravity.
〖WTHZ
2006, 24(1): 68-74.
Abstract:
The concentrations of Mn, Sr, SiO2, Al2O3, and values of δ13C, δ18O and 87Sr/86Sr have been measured for different shell layers of rudist bivalve from a Late Cretaceous section in the south of Tibet. The study results are as follows:
1) The constitution minerals, in the pillar, pearl and transition layers for the shell of rudist bivalve have totally transposed to diagenetic low magnesium calcite (DLMC) by neomorphism and all the original carbonates are recrystallized to a certain extent.
2) The recrystallization of inner shell layers (pearl or transition layer) is much stronger than that of outer shell layer. The outer shell layer, with duller catholuminescence, has pillar texture.
3) The concentration of Sr and value of δ18O displays a regular variety from the outer shell layer (pillar layer) to inner shell layer (pearl layer). The concentration of Sr and value of δ18O for outer shell layer are lower than those of inner shell layer, suggesting that the inner shell layer lost more information of sea water during neomorphism.
4) The δ18O values of all the shell layers and the celom filling are much lower than those of original sea water reported by the published papers, so the exchange with meteoric water (or other diagenetic fluid) in oxygen isotope should have happened during neomorphism of precursory minerals in the shell, but relatively less exchange happened in outer shell layer.
5) The carbon and strontium isotope composition of different shell layers is close to the values of coeval sea water, and no regular variation among different shell layers, indicating less exchange with diagenetic fluid in carbon and strontium isotope. The reason is that diagenetic recrystallization of carbonates is accomplished in a system with a low water / rock ratio for carbon (also for strontium), but a high ratio for oxygen, and therefore the isotope compositions of carbon and strontium contains more information for original sea water.
The concentrations of Mn, Sr, SiO2, Al2O3, and values of δ13C, δ18O and 87Sr/86Sr have been measured for different shell layers of rudist bivalve from a Late Cretaceous section in the south of Tibet. The study results are as follows:
1) The constitution minerals, in the pillar, pearl and transition layers for the shell of rudist bivalve have totally transposed to diagenetic low magnesium calcite (DLMC) by neomorphism and all the original carbonates are recrystallized to a certain extent.
2) The recrystallization of inner shell layers (pearl or transition layer) is much stronger than that of outer shell layer. The outer shell layer, with duller catholuminescence, has pillar texture.
3) The concentration of Sr and value of δ18O displays a regular variety from the outer shell layer (pillar layer) to inner shell layer (pearl layer). The concentration of Sr and value of δ18O for outer shell layer are lower than those of inner shell layer, suggesting that the inner shell layer lost more information of sea water during neomorphism.
4) The δ18O values of all the shell layers and the celom filling are much lower than those of original sea water reported by the published papers, so the exchange with meteoric water (or other diagenetic fluid) in oxygen isotope should have happened during neomorphism of precursory minerals in the shell, but relatively less exchange happened in outer shell layer.
5) The carbon and strontium isotope composition of different shell layers is close to the values of coeval sea water, and no regular variation among different shell layers, indicating less exchange with diagenetic fluid in carbon and strontium isotope. The reason is that diagenetic recrystallization of carbonates is accomplished in a system with a low water / rock ratio for carbon (also for strontium), but a high ratio for oxygen, and therefore the isotope compositions of carbon and strontium contains more information for original sea water.
2006, 24(1): 81-89.
Abstract:
The trace fossils in shoreshallow lacustine sediments in Dainan Formation, Paleogene in Gaoyou Sag, Subei Basin consist of at least 6 ichnogenera, 8 ichnospecies, namely, Taenidium barrette, Taenidium satanassi, Beaconites coronus, Cystichnum curvativum, Palaeophycus isp., Planolites montanus, Skolithos verticalis and Skolithos linearis. These trace fossils were mainly of Fodinichnia and Domichnia of invertebrates, and were preserved in full relief and epirelief. Based on the integrated analysis of assembage traits and paleoenvironments, two ichnoassemblages are recognized: 1) TaenidiumBeaconites assemblage, which is mainly of feeding burrows with crescent backfilled structures，and presents itself in shoreshallow lacustrine sediments under periodically arid climate；2）Skolithos linearis assemblage，which is mainly of dwelling burrows，and presents itself in delta plainfront sediments. Based on analysis of bioturbation variation features, three bioturbation assemblages are identified: 1) homogeneous one, which indicates that the water level might rise slowly within little scope and then be stable for a relatively long time; 2) stronger upwards one, which indicates that the water level was generally stable and might rise within little scope, and then be stable, and fall finally; 3) compound one, which indicates that the water level might rise slowly and then fall slowly. In a fan plainfront distributary channel sedimentary sequence, the genres, abundance, diversity of trace fossils and the bioturbation index exhibit regularity vertically. Based on analysis of sedimentology and ichnology, a distributary channel sequence can be divided into 4 sedimentary sets, and each set exhibits different physical and biologic structures.
The trace fossils in shoreshallow lacustine sediments in Dainan Formation, Paleogene in Gaoyou Sag, Subei Basin consist of at least 6 ichnogenera, 8 ichnospecies, namely, Taenidium barrette, Taenidium satanassi, Beaconites coronus, Cystichnum curvativum, Palaeophycus isp., Planolites montanus, Skolithos verticalis and Skolithos linearis. These trace fossils were mainly of Fodinichnia and Domichnia of invertebrates, and were preserved in full relief and epirelief. Based on the integrated analysis of assembage traits and paleoenvironments, two ichnoassemblages are recognized: 1) TaenidiumBeaconites assemblage, which is mainly of feeding burrows with crescent backfilled structures，and presents itself in shoreshallow lacustrine sediments under periodically arid climate；2）Skolithos linearis assemblage，which is mainly of dwelling burrows，and presents itself in delta plainfront sediments. Based on analysis of bioturbation variation features, three bioturbation assemblages are identified: 1) homogeneous one, which indicates that the water level might rise slowly within little scope and then be stable for a relatively long time; 2) stronger upwards one, which indicates that the water level was generally stable and might rise within little scope, and then be stable, and fall finally; 3) compound one, which indicates that the water level might rise slowly and then fall slowly. In a fan plainfront distributary channel sedimentary sequence, the genres, abundance, diversity of trace fossils and the bioturbation index exhibit regularity vertically. Based on analysis of sedimentology and ichnology, a distributary channel sequence can be divided into 4 sedimentary sets, and each set exhibits different physical and biologic structures.
2006, 24(1): 96-106.
Abstract:
In the geological evolution of Tarim Basin, many transgressions and regressions of the ancient Teris〖KG*2〗happened, especially in the Cretaceous and Tertiary〖KG*2〗period, and brought〖KG*2〗plenty〖KG*2〗of salt sources.〖KG*2〗What's more, because of uttermost drought and proper sedimentary facies and paleogeography, many salt, gypsum, carbonate and mud-salt were〖KG*2〗deposited.〖KG*2〗By our fieldwork, above 300 samples were collected including brine and solid. Among these samples, 43 brine samples and 99 solid halite samples were analyzed. The item of analysis included K+,Na+,Ca2+,Mg2+,Cl-,SO2-4,CO2-3,HCO-3,Br-,B3+〖KG*2〗and so on. This paper discussed the variety of the content of K+〖KG*2〗and the characteristics〖KG*2〗coefficients of geochemistry, the model of salt formation, the concentration stage of brine and the possibility of potash formation by geochemical analysis of the brine from Tarim Basin. In the end, the potash perspective〖KG*2〗was proposed. From the geochemical parameters〖KG*2〗of brine in Western〖KG*2〗Tarim Basin, we could conclude that the perspective of potash〖KG*2〗is Kashi Sag and Yangxia Sag.〖KG*2〗By comparing the content of microelement〖KG*2〗and the geochemical parameters〖KG*2〗of brine with that of normal condensed brine, it is known that there is little microelements〖KG*2〗such as Br and B in Tarim Basin, so we could not completely depend on these indexes to judge the condense stage of brine and halite as well as potash〖KG*2〗resources, and this viewpoint indicates that Tarim Basin is the intricate area of salt formation.
In the geological evolution of Tarim Basin, many transgressions and regressions of the ancient Teris〖KG*2〗happened, especially in the Cretaceous and Tertiary〖KG*2〗period, and brought〖KG*2〗plenty〖KG*2〗of salt sources.〖KG*2〗What's more, because of uttermost drought and proper sedimentary facies and paleogeography, many salt, gypsum, carbonate and mud-salt were〖KG*2〗deposited.〖KG*2〗By our fieldwork, above 300 samples were collected including brine and solid. Among these samples, 43 brine samples and 99 solid halite samples were analyzed. The item of analysis included K+,Na+,Ca2+,Mg2+,Cl-,SO2-4,CO2-3,HCO-3,Br-,B3+〖KG*2〗and so on. This paper discussed the variety of the content of K+〖KG*2〗and the characteristics〖KG*2〗coefficients of geochemistry, the model of salt formation, the concentration stage of brine and the possibility of potash formation by geochemical analysis of the brine from Tarim Basin. In the end, the potash perspective〖KG*2〗was proposed. From the geochemical parameters〖KG*2〗of brine in Western〖KG*2〗Tarim Basin, we could conclude that the perspective of potash〖KG*2〗is Kashi Sag and Yangxia Sag.〖KG*2〗By comparing the content of microelement〖KG*2〗and the geochemical parameters〖KG*2〗of brine with that of normal condensed brine, it is known that there is little microelements〖KG*2〗such as Br and B in Tarim Basin, so we could not completely depend on these indexes to judge the condense stage of brine and halite as well as potash〖KG*2〗resources, and this viewpoint indicates that Tarim Basin is the intricate area of salt formation.
2006, 24(1): 113-122.
Abstract:
By utilizing both modern organic petrological and organic geochemical analytical methods, a comparative study was carried out on the maceral ingredients of the Lower Paleozoic organicrich marine black shale in Sichuan Basin and the Paleogene lacustrine oil shale in Bohai Gulf Basin, and on their relationship with thermal evolution, hydrocarbon generation and expulsion. Our observation and the analytical results demonstrate that the black shale are characterized by high degree of thermal evolution and currently very low concentration of hydrocarbons derived from pyrolysis, and are favorablesource rocks in terms of primary hydrocarbon generation capacity, since they generally contain a relic organic carbon content up to 1%3%. However, the black shale retains a great amount of particulate organicmaterials originated from amorphous organics and relict bitumen derived from oil that has not been expelled completely at the earlier stage of oil generation in preCaledonian. Based on the contents of microsomers and relict bitumen in black shale, the amount of hydrocarbon generation and expulsion in the marine black shale can be calculated, and the contribution of gas regeneration in the reservoir bitumen, particulate organics and relict bitumen in old petroleum deposits toward the formation of the Paleozoic carbonate gas reservoirs in the study area can thus be inferred.
The organicrich Paleogene lacustrine oil shale don't show high degree of thermal evolution, since they are characterized by very high contents in bothS1(free hydrocarbon) and S2(pyrolyzed hydrocarbon), which are 2.048.06 mg.g-1and 8.444.65 mg.g-1, respectively, from pyrolytic analyses. The algae and amorphous organics in oil shale generally show strong yellow fluorescence. Also, extensive fluorescence can be observed among a great amount of laminae and mineral crystallites. These results illustrate that the oil shale are important source rocks at the stage of hydrocarbon generation and expulsion in the study area.
By utilizing both modern organic petrological and organic geochemical analytical methods, a comparative study was carried out on the maceral ingredients of the Lower Paleozoic organicrich marine black shale in Sichuan Basin and the Paleogene lacustrine oil shale in Bohai Gulf Basin, and on their relationship with thermal evolution, hydrocarbon generation and expulsion. Our observation and the analytical results demonstrate that the black shale are characterized by high degree of thermal evolution and currently very low concentration of hydrocarbons derived from pyrolysis, and are favorablesource rocks in terms of primary hydrocarbon generation capacity, since they generally contain a relic organic carbon content up to 1%3%. However, the black shale retains a great amount of particulate organicmaterials originated from amorphous organics and relict bitumen derived from oil that has not been expelled completely at the earlier stage of oil generation in preCaledonian. Based on the contents of microsomers and relict bitumen in black shale, the amount of hydrocarbon generation and expulsion in the marine black shale can be calculated, and the contribution of gas regeneration in the reservoir bitumen, particulate organics and relict bitumen in old petroleum deposits toward the formation of the Paleozoic carbonate gas reservoirs in the study area can thus be inferred.
The organicrich Paleogene lacustrine oil shale don't show high degree of thermal evolution, since they are characterized by very high contents in bothS1(free hydrocarbon) and S2(pyrolyzed hydrocarbon), which are 2.048.06 mg.g-1and 8.444.65 mg.g-1, respectively, from pyrolytic analyses. The algae and amorphous organics in oil shale generally show strong yellow fluorescence. Also, extensive fluorescence can be observed among a great amount of laminae and mineral crystallites. These results illustrate that the oil shale are important source rocks at the stage of hydrocarbon generation and expulsion in the study area.
2006, 24(1): 129-134.
Abstract:
Ordos basin is an important MesozoicCenozoic petroliferous basin in West China. Xifeng Oilfield, in the southwest of Ordos Basin, was discovered in recent years. The crude oil reserve in this oilfield is about 100 million tons. Chloroform fractions of free oil and bound oil，which are extracted from six oil sands of Yanchang Formation in Xifeng oilfield, have been analyzed by GC/MS. The nalkaneones in six samples show an strong odd carbon number predominance, carbon number ranging from C13 to C31. This study shows that thermal evolution(maturity) has an effect on the evolution of nalkaneones. The nalkane2ones distribute in bound oil with low maturity, whereas nalkane3, 4,5,6(or more)ones distribute in free oil with high maturity. That is, with the increase of maturity, the carbonyl group distribution of nalkaneones shifts to the higher homologues isomers. The origin of these nalkaneones has been attributed to microbial production from nfatty acids from bacteria, seaseed and higher plant lipid by βoxidation and decarboxylation. The distribution characteristics of nalkaneonesin different state hydrocarbon can be used in dating petroleum accumulation.
Ordos basin is an important MesozoicCenozoic petroliferous basin in West China. Xifeng Oilfield, in the southwest of Ordos Basin, was discovered in recent years. The crude oil reserve in this oilfield is about 100 million tons. Chloroform fractions of free oil and bound oil，which are extracted from six oil sands of Yanchang Formation in Xifeng oilfield, have been analyzed by GC/MS. The nalkaneones in six samples show an strong odd carbon number predominance, carbon number ranging from C13 to C31. This study shows that thermal evolution(maturity) has an effect on the evolution of nalkaneones. The nalkane2ones distribute in bound oil with low maturity, whereas nalkane3, 4,5,6(or more)ones distribute in free oil with high maturity. That is, with the increase of maturity, the carbonyl group distribution of nalkaneones shifts to the higher homologues isomers. The origin of these nalkaneones has been attributed to microbial production from nfatty acids from bacteria, seaseed and higher plant lipid by βoxidation and decarboxylation. The distribution characteristics of nalkaneonesin different state hydrocarbon can be used in dating petroleum accumulation.
2006, 24(1): 141-147.
Abstract:
Based on the analysis of restraining concentration seal mechanism of mudstone caprock and its formation conditions, by studying formation and evolution law of abnormal pore fluid pressure, this paper tries to study formation and evolution of restraining concentration seal of mudstone caprock. According to the formation and evolution of abnormal pore fluid pressure, this paper has established a method recovering and forecasting the formation and evolution law of abnormal gasbearing concentration. This method can not only recover the formation period of restraining concentration seal of mudstone caprock , but also forecast its evolution process, in the mean time, determine the present evolution stage of restraining concentration seal. The method was applied in recovering and forecasting the evolution of restraining concentration seal of K1qn and K1n1+2〖KG*2〗mudstone of Well Gu11 in Gulong sag of Songliao Basin .The results are in accordance with the actual geological conditions, which indicates that the method is practical to study the formation and evolution of restraining concentration seal of mudstone caprock and the method is effective.
Based on the analysis of restraining concentration seal mechanism of mudstone caprock and its formation conditions, by studying formation and evolution law of abnormal pore fluid pressure, this paper tries to study formation and evolution of restraining concentration seal of mudstone caprock. According to the formation and evolution of abnormal pore fluid pressure, this paper has established a method recovering and forecasting the formation and evolution law of abnormal gasbearing concentration. This method can not only recover the formation period of restraining concentration seal of mudstone caprock , but also forecast its evolution process, in the mean time, determine the present evolution stage of restraining concentration seal. The method was applied in recovering and forecasting the evolution of restraining concentration seal of K1qn and K1n1+2〖KG*2〗mudstone of Well Gu11 in Gulong sag of Songliao Basin .The results are in accordance with the actual geological conditions, which indicates that the method is practical to study the formation and evolution of restraining concentration seal of mudstone caprock and the method is effective.
2006, 24(1): 10-18.
Abstract:
Until the end of 2001, more than 58×109〖KG*2〗barrels OOIP have been discovered with the water depth of greater than 500 m in 18 basins whole world. Among them, 90% of oil and gas reserves discovered in turbite sedimentary system. These are the results of deeply exploration and the progress of science and technology.
The Deepwater Fan System (DWFS) refer to such a sedimentary system which locate in Zhu 2 depression related with the continental margin delta system and developed in lowstand tract since 23.8Ma. The formation of DWFA had an important geological background connected with the uplifting of Tibet Plateau, the expansion of South China Sea, and the global sea level change. The vertical stacked pattern is unique and consist of idealized resevoir-caprock complex. Using the systematic theory, coupled with geological time, space and earth dynamic, discusse the formation of DWFA, and reveal the main controlling factors including the Tibet Plateau Uplifting, mantle bulge, and continuous subsidence of depression, subtle deep faulting systems, sedimeatary supplies of classic sediments from granite area in south of mainland, and the global sea level change.
Until the end of 2001, more than 58×109〖KG*2〗barrels OOIP have been discovered with the water depth of greater than 500 m in 18 basins whole world. Among them, 90% of oil and gas reserves discovered in turbite sedimentary system. These are the results of deeply exploration and the progress of science and technology.
The Deepwater Fan System (DWFS) refer to such a sedimentary system which locate in Zhu 2 depression related with the continental margin delta system and developed in lowstand tract since 23.8Ma. The formation of DWFA had an important geological background connected with the uplifting of Tibet Plateau, the expansion of South China Sea, and the global sea level change. The vertical stacked pattern is unique and consist of idealized resevoir-caprock complex. Using the systematic theory, coupled with geological time, space and earth dynamic, discusse the formation of DWFA, and reveal the main controlling factors including the Tibet Plateau Uplifting, mantle bulge, and continuous subsidence of depression, subtle deep faulting systems, sedimeatary supplies of classic sediments from granite area in south of mainland, and the global sea level change.
2006, 24(1): 28-35.
Abstract:
Detrital sedimentation is the direct record in basin for mountain uplift and erosion. The analysis of detrital minerals, including heavy minerals, is a key means for basinmountain coupling studies. The distribution characteristics of heavy minerals in CretaceousTertiary sandstones, Kuqa depression have been studied systemically in this paper, and chemical compositions of detrital garnets and ilmenites have been analyzed by electronic microprobe. The results illustrate that the provenance area of CretaceousTertiary〖KG*2〗sandstones, Kuqa depression, are mainly composed of sedimentary rocks, metamorphic rocks and little intermediatefelsic igneous rocks.〖KG*2〗The〖KG*2〗garnets in Cretaceous sandstones come from blueschist that〖KG*2〗located in the southwest〖KG*2〗Tianshan and lowgrade metamorphic rocks by lager proportionally. The garnets in Tertiary sandstones enrich almandine, which come from highgrade metamorphic rocks. The provenance of most ilmenites in Cretaceous sandstones is metamorphic rocks, and the proportion of igneous rocks provenance increase in Tertiary. These analysis show that southern Tianshan uplift and erosion extensively from Tertiary, as a result of which the provenance of blue schist〖KG*2〗in Paleozoic accretion from north margin of south〖KG*2〗Tianshan has been curtained. With〖KG*2〗deeply erosion of Tianshan, more and more highgrade metamorphic and igneous rocks are exposed.
Detrital sedimentation is the direct record in basin for mountain uplift and erosion. The analysis of detrital minerals, including heavy minerals, is a key means for basinmountain coupling studies. The distribution characteristics of heavy minerals in CretaceousTertiary sandstones, Kuqa depression have been studied systemically in this paper, and chemical compositions of detrital garnets and ilmenites have been analyzed by electronic microprobe. The results illustrate that the provenance area of CretaceousTertiary〖KG*2〗sandstones, Kuqa depression, are mainly composed of sedimentary rocks, metamorphic rocks and little intermediatefelsic igneous rocks.〖KG*2〗The〖KG*2〗garnets in Cretaceous sandstones come from blueschist that〖KG*2〗located in the southwest〖KG*2〗Tianshan and lowgrade metamorphic rocks by lager proportionally. The garnets in Tertiary sandstones enrich almandine, which come from highgrade metamorphic rocks. The provenance of most ilmenites in Cretaceous sandstones is metamorphic rocks, and the proportion of igneous rocks provenance increase in Tertiary. These analysis show that southern Tianshan uplift and erosion extensively from Tertiary, as a result of which the provenance of blue schist〖KG*2〗in Paleozoic accretion from north margin of south〖KG*2〗Tianshan has been curtained. With〖KG*2〗deeply erosion of Tianshan, more and more highgrade metamorphic and igneous rocks are exposed.
2006, 24(1): 43-49.
Abstract:
The tempestites of Paleogene in Huimin sag was discussed based on cores, rock thin section, granularity analysis and log data. It can be seen that the tempestites in the area studied exist lots of rock types, such as clastic rocks, bioclastic limestone and volcaniclastic rock. The cumulative probability plots and sedimentary structures reflect that the transportation medium has characters of tractive current and gravity flow synchronously. The former has “high slopemultibouncing population1 suspension population” pattern, multisegments pattern and “high slope 1 segment” pattern. The latter has gutter cast, surface of scour, graded bed, massive bedding, hummocky cross stratification (HCS), parallel bedding, ripples, contemporaneous deformation and Fugichnia. The vertical sequence of the tempestites in the study area is Sa1graded bed segment, Sa2homogeneous bedding segment, Sbbiggish waveripple bedding segment, Scparallel bedding and HCS segment, Sdwavy bedding segment, Semudstone segment and Sfnatural lake facies clay rock segment upwards. There are four sedimentary models including autochthonous coarse grain rocks, near source tempestites A, near source tempestites B and distal tempestites .
The tempestites of Paleogene in Huimin sag was discussed based on cores, rock thin section, granularity analysis and log data. It can be seen that the tempestites in the area studied exist lots of rock types, such as clastic rocks, bioclastic limestone and volcaniclastic rock. The cumulative probability plots and sedimentary structures reflect that the transportation medium has characters of tractive current and gravity flow synchronously. The former has “high slopemultibouncing population1 suspension population” pattern, multisegments pattern and “high slope 1 segment” pattern. The latter has gutter cast, surface of scour, graded bed, massive bedding, hummocky cross stratification (HCS), parallel bedding, ripples, contemporaneous deformation and Fugichnia. The vertical sequence of the tempestites in the study area is Sa1graded bed segment, Sa2homogeneous bedding segment, Sbbiggish waveripple bedding segment, Scparallel bedding and HCS segment, Sdwavy bedding segment, Semudstone segment and Sfnatural lake facies clay rock segment upwards. There are four sedimentary models including autochthonous coarse grain rocks, near source tempestites A, near source tempestites B and distal tempestites .
2006, 24(1): 56-67.
Abstract:
The reefs, mainly constructed by algae and with high production reservoir for oil and gas, are developed in several areas of Jiyang Sag in the form of composite deposition, that is, reef core, forereef and back reef. Taking into account of the biogenic components, the algal dolomite, the main component of algal reefs, consisted of Cladosiphonia sinensis, Serpula shandongensis etc., and be of favorable storage capability. Based on the lithological characteristics of reef rocks, the reef types can be divided into algal reefs, algal reef mounds and algal biostromes, among which the algal reefs, are of the best reservoir property. Dolomitization, consortium cementation, atmosphere seepage corrosion and deep embedding effect have great influence on the property of reef reservoir. The reef reservoirs are developed mainly in the neighboring structural platform or brim, according to the matching relation of structure, lithology and stratum, reef reservoirs can be divided into reef stratum, fault blocklithology and lithology types.
The reefs, mainly constructed by algae and with high production reservoir for oil and gas, are developed in several areas of Jiyang Sag in the form of composite deposition, that is, reef core, forereef and back reef. Taking into account of the biogenic components, the algal dolomite, the main component of algal reefs, consisted of Cladosiphonia sinensis, Serpula shandongensis etc., and be of favorable storage capability. Based on the lithological characteristics of reef rocks, the reef types can be divided into algal reefs, algal reef mounds and algal biostromes, among which the algal reefs, are of the best reservoir property. Dolomitization, consortium cementation, atmosphere seepage corrosion and deep embedding effect have great influence on the property of reef reservoir. The reef reservoirs are developed mainly in the neighboring structural platform or brim, according to the matching relation of structure, lithology and stratum, reef reservoirs can be divided into reef stratum, fault blocklithology and lithology types.
2006, 24(1): 75-80.
Abstract:
Analyses of TOC/S, TOC/DOP, S/Fe relationships and STOCFe multiple linear regression were carried out to determine limiting factors for pyrite formation in black shales of the Honggang Member (Lower Eocene Buxin Formation) in the Sanshui Basin. Submember A, showing lower organic carbon and higher iron contents than the other submembers, deposited in oxygenated bottom waters. Bacterial sulfate reduction took place below the sedimentwater interface, and pyrite was formed diagenetically and organic carbon was limited. Submember B and C are characterized by large variations in organic carbon content. Organicrich (TOC>4%) rocks deposited under anoxic environments, in which H2S presented above the sediment water interface as well as within the sediments. Pyrite was formed syngenetically and confined by the duration during which iron detritus reacted with H2S in the water column and by the availability of dissolved sulfate that decreased due to an increasing input of fresh waters. For organicpoor (TOC<4%) sediments, pyrite was of syngenetic and diagenetic. Organic carbonlimited diagenetic pyrite added to the earlier formed syngenetic pyrite, which was controlled by the time that iron minerals remained in contact with H2S in anoxic waters.
Analyses of TOC/S, TOC/DOP, S/Fe relationships and STOCFe multiple linear regression were carried out to determine limiting factors for pyrite formation in black shales of the Honggang Member (Lower Eocene Buxin Formation) in the Sanshui Basin. Submember A, showing lower organic carbon and higher iron contents than the other submembers, deposited in oxygenated bottom waters. Bacterial sulfate reduction took place below the sedimentwater interface, and pyrite was formed diagenetically and organic carbon was limited. Submember B and C are characterized by large variations in organic carbon content. Organicrich (TOC>4%) rocks deposited under anoxic environments, in which H2S presented above the sediment water interface as well as within the sediments. Pyrite was formed syngenetically and confined by the duration during which iron detritus reacted with H2S in the water column and by the availability of dissolved sulfate that decreased due to an increasing input of fresh waters. For organicpoor (TOC<4%) sediments, pyrite was of syngenetic and diagenetic. Organic carbonlimited diagenetic pyrite added to the earlier formed syngenetic pyrite, which was controlled by the time that iron minerals remained in contact with H2S in anoxic waters.
2006, 24(1): 90-95.
Abstract:
Selecting discretion parameter is the key of multiparameters to identify flow units. Taking reservoir of fluvial facies in the area of Well L37 in Ordos basin as an example, utilizing SPSS statistical analysis software, through analyzing the discretions and their connection between six parameters of reservoirs, the discretion function of flow units has been established, the characters of flow units and heterogeneities of reservoirs have been investigated. There are four types of flow units and three kinds of intrastratal heterogeneities, the flow units ofⅠ,Ⅱ,Ⅲ,Ⅳ distributes in sedimentary microfacies of point bar, crevasse, natural levee. Different measures should be adopted according to the characters of reservoir heterogeneities.
Selecting discretion parameter is the key of multiparameters to identify flow units. Taking reservoir of fluvial facies in the area of Well L37 in Ordos basin as an example, utilizing SPSS statistical analysis software, through analyzing the discretions and their connection between six parameters of reservoirs, the discretion function of flow units has been established, the characters of flow units and heterogeneities of reservoirs have been investigated. There are four types of flow units and three kinds of intrastratal heterogeneities, the flow units ofⅠ,Ⅱ,Ⅲ,Ⅳ distributes in sedimentary microfacies of point bar, crevasse, natural levee. Different measures should be adopted according to the characters of reservoir heterogeneities.
2006, 24(1): 107-112.
Abstract:
During the Neoproterozoic, earth suffered through at least two globeengulfing ice age. Researchers proposed “Snowball earth” hypothesis to explain a series of puzzling Neoproterozoic sedimentary recordings. This hypothesis has become an ancient widow for the study of global glaciation and bioradiation aftermath. Other researchers, however, do not agree that the earth has been completely icecovered. They proposed alternative hypotheses, such as “Slushball/ Semifrozen Earth”, and “Thinice”models. Although, each hypothesis cannot explain all the geological and geochemical recordings, more and more evidence, especially, molecular organic geochemical and biological evidences show that the ocean was not entirely icecovered during “Snowball Earth”age. Thin ice sheets or open water zones remained in tropical areas. The open water zone is essential for the survival and evolution of photosynthetic organisms, which would make a significant impact on the “Cambrian Bioradiation” and the evolution of life on the earth.
During the Neoproterozoic, earth suffered through at least two globeengulfing ice age. Researchers proposed “Snowball earth” hypothesis to explain a series of puzzling Neoproterozoic sedimentary recordings. This hypothesis has become an ancient widow for the study of global glaciation and bioradiation aftermath. Other researchers, however, do not agree that the earth has been completely icecovered. They proposed alternative hypotheses, such as “Slushball/ Semifrozen Earth”, and “Thinice”models. Although, each hypothesis cannot explain all the geological and geochemical recordings, more and more evidence, especially, molecular organic geochemical and biological evidences show that the ocean was not entirely icecovered during “Snowball Earth”age. Thin ice sheets or open water zones remained in tropical areas. The open water zone is essential for the survival and evolution of photosynthetic organisms, which would make a significant impact on the “Cambrian Bioradiation” and the evolution of life on the earth.
2006, 24(1): 123-128.
Abstract:
The maturity of lacustrine oils in Huqing oilfield is low, and the role of biodegradation is poor. Rich carbazole compounds, including carbazole, alkylcarbazole and benzocarbazoles were detected by GC/MS in lacustrine oils from Huqing oilfield. The results indicate the maturity plays an important role on the concentration of carbazole compounds and its relative contents, and the biodegradation plays weak role on the carbazole compounds. The concentration of carbazole compounds, the ratio of alkylcarbazole/benzocarbazole and the benzocarbazole ratio are not suitable to be the indicator of the oil migration, which are mainly controlled〖KG*2〗by the maturity of lacustrine oils, and the isomer ratio of dimethycarbazole is still a good parameter of the oil migration.
The maturity of lacustrine oils in Huqing oilfield is low, and the role of biodegradation is poor. Rich carbazole compounds, including carbazole, alkylcarbazole and benzocarbazoles were detected by GC/MS in lacustrine oils from Huqing oilfield. The results indicate the maturity plays an important role on the concentration of carbazole compounds and its relative contents, and the biodegradation plays weak role on the carbazole compounds. The concentration of carbazole compounds, the ratio of alkylcarbazole/benzocarbazole and the benzocarbazole ratio are not suitable to be the indicator of the oil migration, which are mainly controlled〖KG*2〗by the maturity of lacustrine oils, and the isomer ratio of dimethycarbazole is still a good parameter of the oil migration.
2006, 24(1): 135-140.
Abstract:
δ13C1，δ13C2,δ13C3，δ13C4 of〖KG*2〗natural gas isotopic composition are various in different parts of Qaidam Basin. The average〖KG*2〗of them are －23.1‰,－24.1‰,－22.7‰ and〖KG*2〗－23.6‰ in Sanhu area around; －29.8‰,－24.7‰,－23.1‰ and〖KG*2〗－22.9‰ in Chaibeiyuan area;〖KG*2〗－39.2‰,－26.8‰,－23‰ and〖KG*2〗－23‰ in Chaixi area;〖KG*2〗－67.8‰,－39.2‰，－32.3‰ and lack of〖KG*2〗δ13C4 in Sanhu area. δ13C4>δ13C3〖KG*2〗>δ13C2〖KG*2〗>δ13C1 exist between〖KG*2〗component of most natural〖KG*2〗gas isotope, and reversion〖KG*2〗of minor heavy carbon isotopic composition exist. Reginally,δ13C1，δ13C2,δ13C3，δ13C4 of〖KG*2〗natural gas isotopic composition〖KG*2〗decrease gradually from〖KG*2〗Sanhu area around,〖KG*2〗Chaibeiyuan area and Chaixi area to Sanhu area.〖KG*2〗δ13C2-δ13C1〖KG*2〗andδ13C3-δ13C2 of〖KG*2〗natural gas isotopic composition increase gradually from〖KG*2〗Sanhu area around,〖KG*2〗Chaibeiyuan area and Chaixi area to Sanhu area, the average〖KG*2〗of them are －0.8‰ and〖KG*2〗－0.9‰ in〖KG*2〗Sanhu area around, 5.1‰ and 1.3‰ in Chaibeiyuan area，14.5‰ and 2.3‰ in Chaixi area， 27.9‰ and 12.5‰ in Sanhu area.
δ13C4>δ13C3〖KG*2〗>δ13C2〖KG*2〗>δ13C1 exist between〖KG*2〗component of most natural〖KG*2〗gas isotope because natural〖KG*2〗gas of organic geneses are derived from the similar process of thermodynamic action, and reversion〖KG*2〗of minor heavy carbon isotopic composition exist because of the mixed action of natural gas from the different derivation or the difference of duration, temperatures and pressures〖KG*2〗in developing hydrocarbon process from the same source rock. The difference between δ13C2-δ13C1〖KG*2〗and δ13C3-δ13C2〖KG*2〗in different area depend on duration, temperatures and pressures〖KG*2〗of source rock evolution, the higher temperatures and pressures〖KG*2〗and the longer duration of source rock evolution, the more uniform〖KG*2〗δ13C distribution between natural〖KG*2〗gas component. In the meantime, bacteria and types of kerogen have an effect on δ13C2-δ13C1〖KG*2〗andδ13C3-δ13C2 to some extent. The study on carbon isotope geochemical characteristic. can not only divide types of natural〖KG*2〗gas and discuss〖KG*2〗their geneses in theory, but also guide the exploration of natural〖KG*2〗gas.
δ13C1，δ13C2,δ13C3，δ13C4 of〖KG*2〗natural gas isotopic composition are various in different parts of Qaidam Basin. The average〖KG*2〗of them are －23.1‰,－24.1‰,－22.7‰ and〖KG*2〗－23.6‰ in Sanhu area around; －29.8‰,－24.7‰,－23.1‰ and〖KG*2〗－22.9‰ in Chaibeiyuan area;〖KG*2〗－39.2‰,－26.8‰,－23‰ and〖KG*2〗－23‰ in Chaixi area;〖KG*2〗－67.8‰,－39.2‰，－32.3‰ and lack of〖KG*2〗δ13C4 in Sanhu area. δ13C4>δ13C3〖KG*2〗>δ13C2〖KG*2〗>δ13C1 exist between〖KG*2〗component of most natural〖KG*2〗gas isotope, and reversion〖KG*2〗of minor heavy carbon isotopic composition exist. Reginally,δ13C1，δ13C2,δ13C3，δ13C4 of〖KG*2〗natural gas isotopic composition〖KG*2〗decrease gradually from〖KG*2〗Sanhu area around,〖KG*2〗Chaibeiyuan area and Chaixi area to Sanhu area.〖KG*2〗δ13C2-δ13C1〖KG*2〗andδ13C3-δ13C2 of〖KG*2〗natural gas isotopic composition increase gradually from〖KG*2〗Sanhu area around,〖KG*2〗Chaibeiyuan area and Chaixi area to Sanhu area, the average〖KG*2〗of them are －0.8‰ and〖KG*2〗－0.9‰ in〖KG*2〗Sanhu area around, 5.1‰ and 1.3‰ in Chaibeiyuan area，14.5‰ and 2.3‰ in Chaixi area， 27.9‰ and 12.5‰ in Sanhu area.
δ13C4>δ13C3〖KG*2〗>δ13C2〖KG*2〗>δ13C1 exist between〖KG*2〗component of most natural〖KG*2〗gas isotope because natural〖KG*2〗gas of organic geneses are derived from the similar process of thermodynamic action, and reversion〖KG*2〗of minor heavy carbon isotopic composition exist because of the mixed action of natural gas from the different derivation or the difference of duration, temperatures and pressures〖KG*2〗in developing hydrocarbon process from the same source rock. The difference between δ13C2-δ13C1〖KG*2〗and δ13C3-δ13C2〖KG*2〗in different area depend on duration, temperatures and pressures〖KG*2〗of source rock evolution, the higher temperatures and pressures〖KG*2〗and the longer duration of source rock evolution, the more uniform〖KG*2〗δ13C distribution between natural〖KG*2〗gas component. In the meantime, bacteria and types of kerogen have an effect on δ13C2-δ13C1〖KG*2〗andδ13C3-δ13C2 to some extent. The study on carbon isotope geochemical characteristic. can not only divide types of natural〖KG*2〗gas and discuss〖KG*2〗their geneses in theory, but also guide the exploration of natural〖KG*2〗gas.
2006, 24(1): 148-152.
Abstract:
Complexand levityof geological conditions for forming oil reservoirs result inthe complex nd levityof oil/water distribution, especially, in low permeability reservoirs. There have one kind of oil/water inversion in fault trap and lithologic oil reservoirs, that is, from the high portions of the single sandstone body to the low portions, they are water layer, waterbearing layer, oilwater layer, oil layer, oilwater layer, waterbearing layer, and water layer. According to analysis on the controlling factors of the oil/water inverted distribution in low permeability reservoirs, two kinds of genesis mechanisms were discussed. The results indicate hat there have two status. First, in fault rap, the history diversity f the fault sealing is the key reason for the oil/water inverted distribution and physical properties of reservoir and permeability difference are the second reason. Second, in upward wedge out sandstone,physical properties of reservoir and its levity, especially, the heterogeneity of layer, are the key reasons for the oil/water inverted distribution. Meanwhile,The results indicate hat they include the lowresistivity pay zone in the oil/water inversion system.
Complexand levityof geological conditions for forming oil reservoirs result inthe complex nd levityof oil/water distribution, especially, in low permeability reservoirs. There have one kind of oil/water inversion in fault trap and lithologic oil reservoirs, that is, from the high portions of the single sandstone body to the low portions, they are water layer, waterbearing layer, oilwater layer, oil layer, oilwater layer, waterbearing layer, and water layer. According to analysis on the controlling factors of the oil/water inverted distribution in low permeability reservoirs, two kinds of genesis mechanisms were discussed. The results indicate hat there have two status. First, in fault rap, the history diversity f the fault sealing is the key reason for the oil/water inverted distribution and physical properties of reservoir and permeability difference are the second reason. Second, in upward wedge out sandstone,physical properties of reservoir and its levity, especially, the heterogeneity of layer, are the key reasons for the oil/water inverted distribution. Meanwhile,The results indicate hat they include the lowresistivity pay zone in the oil/water inversion system.
