The Lower Cambrian shale gas in the western Hubei area,South China has a great resource prospect,but the gas-in-place(GIP)content in different sedimentary facies varies widely,and the relevant mechanism has been not w...The Lower Cambrian shale gas in the western Hubei area,South China has a great resource prospect,but the gas-in-place(GIP)content in different sedimentary facies varies widely,and the relevant mechanism has been not well understood.In the present study,two sets of the Lower Cambrian shale samples from the Wells YD4 and YD5 in the western Hubei area,representing the deep-water shelf facies and shallowwater platform facies,respectively,were investigated on the differences of pore types,pore structure and methane adsorption capacity between them,and the main controlling factor and mechanism of their methane adsorption capacities and GIP contents were discussed.The results show that the organic matter(OM)pores in the YD4 shale samples are dominant,while the inorganic mineral(IM)pores in the YD5 shale samples are primary,with underdeveloped OM pores.The pore specific surface area(SSA)and pore volume(PV)of the YD4 shale samples are mainly from micropores and mesopores,respectively,while those of the YD5 shale samples are mainly from micropores and macropores,respectively.The methane adsorption capacity of the YD4 shale samples is significantly higher than that of the YD5 shale samples,with a maximum absolute adsorption capacity of 3.13 cm^(3)/g and 1.31 cm^(3)/g in average,respectively.Compared with the shallow-water platform shale,the deep-water shelf shale has a higher TOC content,a better kerogen type and more developed OM pores,which is the main mechanism for its higher adsorption capacity.The GIP content models based on two samples with a similar TOC content selected respectively from the Wells YD4 and YD5 further indicate that the GIP content of the deep-water shelf shale is mainly 34 m^(3)/t within a depth range of 1000—4000 m,with shale gas exploration and development potential,while the shallow-water platform shale has normally a GIP content of<1 m^(3)/t,with little shale gas potential.Considering the geological and geochemical conditions of shale gas formation and preservation,the deep-water shelf facies is the most favorable target for the Lower Cambrian shale gas exploration and development in the western Hubei area,South China.展开更多
Control of various factors, including mineral components, primary productivity and redox level, on the total organic carbon(TOC) in the lower Cambrian black shale from southeastern margin of Upper Yangtze(Taozichong, ...Control of various factors, including mineral components, primary productivity and redox level, on the total organic carbon(TOC) in the lower Cambrian black shale from southeastern margin of Upper Yangtze(Taozichong, Longbizui and Yanbei areas) is discussed in detail in this article. Mineral components in the study strata are dominated by quartz and clay minerals. Quartz in the Niutitang Formation is mainly of biogenic origin, and the content is in positive correlation with TOC, while the content of clay minerals is negatively correlated with TOC. Primary productivity, represented by the content of Mobio(biogenic molybdenum), Babio(biogenic barium) and phosphorus, is positively correlated with TOC. The main alkanes in studied samples are nCC, and odd–even priority values are closed to 1(0.73–1.13), which suggest the organic matter source was marine plankton. Element content ratios of U/Th and Ni/Co and compound ratio Pr/Ph indicate dysoxic–anoxic bottom water, with weak positive relative with TOC. In total, three main points can be drawn to explain the relationship between data and the factors affecting organic accumulation:(1) quartz-rich and clay-mineral-poor deep shelf–slope–basin environment was favorable for living organisms;(2) high productivity provided the material foundation for organic generation;(3) the redox conditions impact slightly on the content of organic matter under high productivity and dysoxic–anoxic condition.展开更多
The study on Lower Cambrian dolostones in Tarim Basin can improve our understanding of ancient and deeply buried carbonate reservoirs.In this research,diagenetic fluid characteristics and their control on porosity evo...The study on Lower Cambrian dolostones in Tarim Basin can improve our understanding of ancient and deeply buried carbonate reservoirs.In this research,diagenetic fluid characteristics and their control on porosity evolution have been revealed by studying the petrography and in situ geochemistry of different dolomites.Three types of diagenetic fluids were identified:(1) Replacive dolomites were deviated from shallow burial dolomitizing fluids,which might probably be concentrated ancient seawater at early stage.(2) Fine-to-medium crystalline,planar-e diamond pore-filling dolomites(Fd1) were likely slowly and sufficiently crystallized from deep-circulating crustal hydrothermal fluids during Devonian.(3) Coarse crystalline,non-planar-a saddle pore-filling dolomites(Fd2) might rapidly and insufficiently crystallize from magmatic hydrothermal fluids during Permian.Early dolomitizing fluids did not increase the porosity,but transformed the primary pores to dissolution pores through dolomitization.Deep-circulating crustal hydrothermal fluids significantly increased porosity in the early stages by dissolving and then slightly decreased the porosity in the late stage due to Fd1 precipitation.Magmatic hydrothermal fluids only precipitated the Fd2 dolomites and slightly decreased the porosity.In summary,Devonian deep-circulating crustal hydrothermal fluids dominated the porosity evolution of the Lower Cambrian dolostone reservoir in the Tarim Basin.展开更多
Using field geological survey,drilling and seismic data,combined with the study of regional tectonic evolution and structural deformation,as well as lithological and sedimentary analysis,we reconstructed the basin fil...Using field geological survey,drilling and seismic data,combined with the study of regional tectonic evolution and structural deformation,as well as lithological and sedimentary analysis,we reconstructed the basin filling process and paleo-geography of north Tarim Basin in Early Cambrian,aiming to analyze the factors controlling the distribution and spatial architecture of the subsalt reservoir and source units and to define the favorable exploration direction.The Late Sinian tectonic activities in the northern Tarim Basin were characterized by different patterns in different areas,which controlled the sedimentary pattern in the Early Cambrian.The boundary faults of Nanhuaian rift basin in the south slope of Tabei uplift and the north slope of Tazhong uplift became reactivated in the Early Cambrian,forming two NEE and EW striking subsidence centers and depocenters,where the predicted thickness of the Yurtusi Formation could reach 250 meters.In the Xiaoerbulake period,the weak rimmed platform was developed in the hanging wall of syndepositional fault.Whereas the Nanhuaian rift system in the Tadong and Manxi areas were uplifted and destroyed in the Late Sinian,and appeared as gently slope transiting toward the subsidence center in the Early Cambrian.The former had the sedimentary features of hybrid facies platform and the latter had the sedimentary features of ramp platform.The black shale of the Yurtus Formation in the footwall of syndepositional fault and the reef bank of Xiaoerbulake Formation platform margin in the hanging wall in Early Cambrian constitute a predicable source-reservoir combination.The activity intensity of syndepositional fault controlled the thickness of black shale and the scale of the reef bank.It is suggested carrying out high accuracy seismic exploration to determine the location of Early Cambrian syndepositional faults,on this basis,to search the reef bank of Xiaoerbulake Formation along the faults westward,and then drill risk exploration wells at sites where traps are shallow in buried depth.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.42030804 and 42330811)the“Deep-time Digital Earth”Science and Technology Leading Talents Team Funds for the Central Universities for the Frontiers Science Center for Deep-time Digital Earth,China University of Geosciences(Beijing)(Fundamental Research Funds for the Central UniversitiesGrant No.2652023001)。
文摘The Lower Cambrian shale gas in the western Hubei area,South China has a great resource prospect,but the gas-in-place(GIP)content in different sedimentary facies varies widely,and the relevant mechanism has been not well understood.In the present study,two sets of the Lower Cambrian shale samples from the Wells YD4 and YD5 in the western Hubei area,representing the deep-water shelf facies and shallowwater platform facies,respectively,were investigated on the differences of pore types,pore structure and methane adsorption capacity between them,and the main controlling factor and mechanism of their methane adsorption capacities and GIP contents were discussed.The results show that the organic matter(OM)pores in the YD4 shale samples are dominant,while the inorganic mineral(IM)pores in the YD5 shale samples are primary,with underdeveloped OM pores.The pore specific surface area(SSA)and pore volume(PV)of the YD4 shale samples are mainly from micropores and mesopores,respectively,while those of the YD5 shale samples are mainly from micropores and macropores,respectively.The methane adsorption capacity of the YD4 shale samples is significantly higher than that of the YD5 shale samples,with a maximum absolute adsorption capacity of 3.13 cm^(3)/g and 1.31 cm^(3)/g in average,respectively.Compared with the shallow-water platform shale,the deep-water shelf shale has a higher TOC content,a better kerogen type and more developed OM pores,which is the main mechanism for its higher adsorption capacity.The GIP content models based on two samples with a similar TOC content selected respectively from the Wells YD4 and YD5 further indicate that the GIP content of the deep-water shelf shale is mainly 34 m^(3)/t within a depth range of 1000—4000 m,with shale gas exploration and development potential,while the shallow-water platform shale has normally a GIP content of<1 m^(3)/t,with little shale gas potential.Considering the geological and geochemical conditions of shale gas formation and preservation,the deep-water shelf facies is the most favorable target for the Lower Cambrian shale gas exploration and development in the western Hubei area,South China.
基金supported by the National Natural Science Foundation Research (Grant 41672130, 41728004)the National Key S&T Special Projects (Grant 2016ZX05061-003-001)+1 种基金the National Postdoctoral Innovative Talent Support Program (Grant BX201700289)China Postdoctoral Science Foundation (Grant 2017M620296)
文摘Control of various factors, including mineral components, primary productivity and redox level, on the total organic carbon(TOC) in the lower Cambrian black shale from southeastern margin of Upper Yangtze(Taozichong, Longbizui and Yanbei areas) is discussed in detail in this article. Mineral components in the study strata are dominated by quartz and clay minerals. Quartz in the Niutitang Formation is mainly of biogenic origin, and the content is in positive correlation with TOC, while the content of clay minerals is negatively correlated with TOC. Primary productivity, represented by the content of Mobio(biogenic molybdenum), Babio(biogenic barium) and phosphorus, is positively correlated with TOC. The main alkanes in studied samples are nCC, and odd–even priority values are closed to 1(0.73–1.13), which suggest the organic matter source was marine plankton. Element content ratios of U/Th and Ni/Co and compound ratio Pr/Ph indicate dysoxic–anoxic bottom water, with weak positive relative with TOC. In total, three main points can be drawn to explain the relationship between data and the factors affecting organic accumulation:(1) quartz-rich and clay-mineral-poor deep shelf–slope–basin environment was favorable for living organisms;(2) high productivity provided the material foundation for organic generation;(3) the redox conditions impact slightly on the content of organic matter under high productivity and dysoxic–anoxic condition.
基金funded by the National Basic Research Program of China (Grant 2012CB214801)Tarim Oilfield Branch of Petro China (Grant 041013100042)。
文摘The study on Lower Cambrian dolostones in Tarim Basin can improve our understanding of ancient and deeply buried carbonate reservoirs.In this research,diagenetic fluid characteristics and their control on porosity evolution have been revealed by studying the petrography and in situ geochemistry of different dolomites.Three types of diagenetic fluids were identified:(1) Replacive dolomites were deviated from shallow burial dolomitizing fluids,which might probably be concentrated ancient seawater at early stage.(2) Fine-to-medium crystalline,planar-e diamond pore-filling dolomites(Fd1) were likely slowly and sufficiently crystallized from deep-circulating crustal hydrothermal fluids during Devonian.(3) Coarse crystalline,non-planar-a saddle pore-filling dolomites(Fd2) might rapidly and insufficiently crystallize from magmatic hydrothermal fluids during Permian.Early dolomitizing fluids did not increase the porosity,but transformed the primary pores to dissolution pores through dolomitization.Deep-circulating crustal hydrothermal fluids significantly increased porosity in the early stages by dissolving and then slightly decreased the porosity in the late stage due to Fd1 precipitation.Magmatic hydrothermal fluids only precipitated the Fd2 dolomites and slightly decreased the porosity.In summary,Devonian deep-circulating crustal hydrothermal fluids dominated the porosity evolution of the Lower Cambrian dolostone reservoir in the Tarim Basin.
基金Supported by the National Key Research and Development Program of China(2017YFC0603101)Strategic Priority Research Program of the Chinese Academy of Sciences(XDA14010101)Scientific Research and Technological Development Project of PetroChina(2018A-01).
文摘Using field geological survey,drilling and seismic data,combined with the study of regional tectonic evolution and structural deformation,as well as lithological and sedimentary analysis,we reconstructed the basin filling process and paleo-geography of north Tarim Basin in Early Cambrian,aiming to analyze the factors controlling the distribution and spatial architecture of the subsalt reservoir and source units and to define the favorable exploration direction.The Late Sinian tectonic activities in the northern Tarim Basin were characterized by different patterns in different areas,which controlled the sedimentary pattern in the Early Cambrian.The boundary faults of Nanhuaian rift basin in the south slope of Tabei uplift and the north slope of Tazhong uplift became reactivated in the Early Cambrian,forming two NEE and EW striking subsidence centers and depocenters,where the predicted thickness of the Yurtusi Formation could reach 250 meters.In the Xiaoerbulake period,the weak rimmed platform was developed in the hanging wall of syndepositional fault.Whereas the Nanhuaian rift system in the Tadong and Manxi areas were uplifted and destroyed in the Late Sinian,and appeared as gently slope transiting toward the subsidence center in the Early Cambrian.The former had the sedimentary features of hybrid facies platform and the latter had the sedimentary features of ramp platform.The black shale of the Yurtus Formation in the footwall of syndepositional fault and the reef bank of Xiaoerbulake Formation platform margin in the hanging wall in Early Cambrian constitute a predicable source-reservoir combination.The activity intensity of syndepositional fault controlled the thickness of black shale and the scale of the reef bank.It is suggested carrying out high accuracy seismic exploration to determine the location of Early Cambrian syndepositional faults,on this basis,to search the reef bank of Xiaoerbulake Formation along the faults westward,and then drill risk exploration wells at sites where traps are shallow in buried depth.
