Although carbon isotope reversal and its reasons in shale gas reservoirs have been widely recognized,the application of the reversal is yet to be investigated.A study on high-maturity shale from Wufeng and Longmaxi Fo...Although carbon isotope reversal and its reasons in shale gas reservoirs have been widely recognized,the application of the reversal is yet to be investigated.A study on high-maturity shale from Wufeng and Longmaxi Formations in the Sichuan Basin not only reveals the relationship between the degree of isotopes inversion and the production capacity(e.g.,estimated ultimate recovery(EUR))of the gas well but also indicates the preservation conditions of shale gas reservoirs.(1)Although there are differences in gas isotopes in different shale gas reservoirs,the isotope fractionation of shale gas is small during the production stage of gas wells,even when the wellbore pressure drops to zero.The main cause of the difference in carbon isotopes and their inversion degree can be the uplift time during the Yanshan period and the formation pressure relief degree of shale gas reservoirs in distinct structural positions.Thus,carbon isotope inversion is a good indicator of shale gas preservation condition and EUR of shale gas wells.(2)The degree of carbon isotope inversion correlates strongly with shale gas content and EUR.The calculation formula of shale-gas recoverable reserves was established using△δ^(13)C(δC_(1)-δC_(2))and EUR.(3)The gas loss rate and total loss amount can be estimated using the dynamic reserves and isotopic difference values of gas wells in various shale gas fields,which also reflects the current methane loss,thereby demonstrating great potential for evaluating global methane loss in shales.展开更多
China’s helium resource is highly dependent on overseas imports.Organic-rich and U/Th-rich shale reservoirs generally contain helium,and although the helium content is low,the total reserve is large.Therefore,the eff...China’s helium resource is highly dependent on overseas imports.Organic-rich and U/Th-rich shale reservoirs generally contain helium,and although the helium content is low,the total reserve is large.Therefore,the effective development and utilisation of shale-type helium resources is a realistic way to improve the security of helium resources in China.In this study,the generation mechanism,helium source and content,migration modes and pathways,controlling factors of enrichment,distribution pattern,and resource potential of the helium were analysed,using the Wufeng-Longmaxi shale in the Sichuan Basin and its periphery.Furthermore,countermeasures were proposed for shale-type helium exploration and development.The results show that the Wufeng-Longmaxi shale has a high content of U and Th and a good ability to generate helium.The helium is generated by a typical crustal source of helium and is characterised by self-generation,self-storage,and wide distribution.The helium resource potential is a product of its content and the resources of the associated natural gas.The continuous supply of helium and effective preservation are the main geological factors that control the enrichment of shale-type helium.The preliminary evaluation results show that the reserves of helium in proven shale gas reserves are 10.8×10^(8)m^(3)in the Sichuan Basin and its periphery,where the extra-large helium fields are likely to be discovered.Additionally,0.0912×10^(8)m^(3)of helium was produced,along with the annual production of shale gas.To avoid the waste of helium and to improve the self-supply ability,it is suggested that research on the resource potential,enrichment mechanism,and distribution pattern of shale-type helium should be carried out as soon as possible,and helium extraction techniques for helium-bearing natural gas should be studied.展开更多
The assessment of gas storage capacity is crucial to furthering shale gas exploration and development in the eastern Sichuan Basin,China.Eleven organic-rich shale samples were selected to carry out the high pressure m...The assessment of gas storage capacity is crucial to furthering shale gas exploration and development in the eastern Sichuan Basin,China.Eleven organic-rich shale samples were selected to carry out the high pressure methane sorption,low-pressure N_(2)/CO_(2) gas adsorption,and bulk and skeletal density measurements to investigate the methane storage capacity(MSC).Based on the relative content of clay,carbonates,quartz+feldspar,we grouped the 11 samples into three lithofacies:silica-rich argillaceous shale(CM-1),argillaceous/siliceous mixed shale(M-2),and clay-rich siliceous shale(S-3).The total porosity of the shale samples varies from 3.4% to 5.6%,and gas saturation ranges from 47% to 89%.The measured total gas amount ranges from 1.84 mg/g to 4.22 mg/g with the ratio of free gas to total gas amount ranging from 52.7% to 70.8%.Free gas with high content in the eastern Sichuan Basin may be the key factor controlling amount of shale gas production.The TOC content critically controls the MSC of shales,because micropore,mesopore volumes and the specific surface areas associated with organic matter provide the storage sites for the free and adsorbed gas.The methane sorption capacities of samples from different lithofacies are also affected by clay minerals and moisture content.Clay minerals can provide additional surface areas for methane sorption,and water can cause a 7.1%-42.8% loss of methane sorption capacity.The total porosity,gas-bearing porosity,water saturation,free gas and adsorbed gas number of samples from different lithofacies show subtle differences if the shale samples had similar TOC contents.Our results suggest that,in the eastern Sichuan Basin,clay-rich shale lithofacies is also prospecting targets for shale gas production.展开更多
It is essential to investigate shale lithofacies distribution and controlling factor of the shale for geological evaluation of shale gas exploration and development.Through comprehensive analysis of cores,thin section...It is essential to investigate shale lithofacies distribution and controlling factor of the shale for geological evaluation of shale gas exploration and development.Through comprehensive analysis of cores,thin sections,cathode luminescence,whole-rock X-ray diffraction,element capture spectroscopy,major/trace element and other data,three major types and eight sub-type shale lithofacies in the shale of Wufeng Formation-Member 1 of Longmaxi Formation in Jiaoshiba area are identified by the three-end-member method and shale lithological classification nomenclature,and the spatiotemporal distribution law and main development controlling factors of shale lithofacies are well studied.In the Jiaoshiba area,vertically,the marine shale develops siliceous shale,mixed shale and argillaceous shale from bottom to top.Besides,lateral distribution of the shale is different from north to south;the shale lithofacies in the north area changes rapidly,the mixed shale in the north area is much thicker than that in the south area,while the siliceous shale in the south area is relatively thicker.Difference in the shale lithofacies is controlled by special sedimentary geologic events;development of the siliceous shale is controlled by the Ordovician-Silurian global volcanic event to some extent,while the mixed shale is significantly influenced by effect of bottom current,and the argillaceous shale is mainly affected by supply of terrestrial clastic material.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.41872124,42202175&No.42130803)。
文摘Although carbon isotope reversal and its reasons in shale gas reservoirs have been widely recognized,the application of the reversal is yet to be investigated.A study on high-maturity shale from Wufeng and Longmaxi Formations in the Sichuan Basin not only reveals the relationship between the degree of isotopes inversion and the production capacity(e.g.,estimated ultimate recovery(EUR))of the gas well but also indicates the preservation conditions of shale gas reservoirs.(1)Although there are differences in gas isotopes in different shale gas reservoirs,the isotope fractionation of shale gas is small during the production stage of gas wells,even when the wellbore pressure drops to zero.The main cause of the difference in carbon isotopes and their inversion degree can be the uplift time during the Yanshan period and the formation pressure relief degree of shale gas reservoirs in distinct structural positions.Thus,carbon isotope inversion is a good indicator of shale gas preservation condition and EUR of shale gas wells.(2)The degree of carbon isotope inversion correlates strongly with shale gas content and EUR.The calculation formula of shale-gas recoverable reserves was established using△δ^(13)C(δC_(1)-δC_(2))and EUR.(3)The gas loss rate and total loss amount can be estimated using the dynamic reserves and isotopic difference values of gas wells in various shale gas fields,which also reflects the current methane loss,thereby demonstrating great potential for evaluating global methane loss in shales.
基金supported by the National Natural Science Foundation of China(Grant Nos.42141021,41872124&42130803).
文摘China’s helium resource is highly dependent on overseas imports.Organic-rich and U/Th-rich shale reservoirs generally contain helium,and although the helium content is low,the total reserve is large.Therefore,the effective development and utilisation of shale-type helium resources is a realistic way to improve the security of helium resources in China.In this study,the generation mechanism,helium source and content,migration modes and pathways,controlling factors of enrichment,distribution pattern,and resource potential of the helium were analysed,using the Wufeng-Longmaxi shale in the Sichuan Basin and its periphery.Furthermore,countermeasures were proposed for shale-type helium exploration and development.The results show that the Wufeng-Longmaxi shale has a high content of U and Th and a good ability to generate helium.The helium is generated by a typical crustal source of helium and is characterised by self-generation,self-storage,and wide distribution.The helium resource potential is a product of its content and the resources of the associated natural gas.The continuous supply of helium and effective preservation are the main geological factors that control the enrichment of shale-type helium.The preliminary evaluation results show that the reserves of helium in proven shale gas reserves are 10.8×10^(8)m^(3)in the Sichuan Basin and its periphery,where the extra-large helium fields are likely to be discovered.Additionally,0.0912×10^(8)m^(3)of helium was produced,along with the annual production of shale gas.To avoid the waste of helium and to improve the self-supply ability,it is suggested that research on the resource potential,enrichment mechanism,and distribution pattern of shale-type helium should be carried out as soon as possible,and helium extraction techniques for helium-bearing natural gas should be studied.
基金funding supports from the Major Programs of National Natural Science Foundation of China(Nos.41690134 and 41690131)the National Natural Science Foundation of China(No.41872139).
文摘The assessment of gas storage capacity is crucial to furthering shale gas exploration and development in the eastern Sichuan Basin,China.Eleven organic-rich shale samples were selected to carry out the high pressure methane sorption,low-pressure N_(2)/CO_(2) gas adsorption,and bulk and skeletal density measurements to investigate the methane storage capacity(MSC).Based on the relative content of clay,carbonates,quartz+feldspar,we grouped the 11 samples into three lithofacies:silica-rich argillaceous shale(CM-1),argillaceous/siliceous mixed shale(M-2),and clay-rich siliceous shale(S-3).The total porosity of the shale samples varies from 3.4% to 5.6%,and gas saturation ranges from 47% to 89%.The measured total gas amount ranges from 1.84 mg/g to 4.22 mg/g with the ratio of free gas to total gas amount ranging from 52.7% to 70.8%.Free gas with high content in the eastern Sichuan Basin may be the key factor controlling amount of shale gas production.The TOC content critically controls the MSC of shales,because micropore,mesopore volumes and the specific surface areas associated with organic matter provide the storage sites for the free and adsorbed gas.The methane sorption capacities of samples from different lithofacies are also affected by clay minerals and moisture content.Clay minerals can provide additional surface areas for methane sorption,and water can cause a 7.1%-42.8% loss of methane sorption capacity.The total porosity,gas-bearing porosity,water saturation,free gas and adsorbed gas number of samples from different lithofacies show subtle differences if the shale samples had similar TOC contents.Our results suggest that,in the eastern Sichuan Basin,clay-rich shale lithofacies is also prospecting targets for shale gas production.
基金The work was supported by supported by the National Science and Technology Major Project of China(2016ZX05060)the National Natural Science Foundation of China(No.41602147,No.41702149)the China Postdoctoral Science Foundation(2017M622559).
文摘It is essential to investigate shale lithofacies distribution and controlling factor of the shale for geological evaluation of shale gas exploration and development.Through comprehensive analysis of cores,thin sections,cathode luminescence,whole-rock X-ray diffraction,element capture spectroscopy,major/trace element and other data,three major types and eight sub-type shale lithofacies in the shale of Wufeng Formation-Member 1 of Longmaxi Formation in Jiaoshiba area are identified by the three-end-member method and shale lithological classification nomenclature,and the spatiotemporal distribution law and main development controlling factors of shale lithofacies are well studied.In the Jiaoshiba area,vertically,the marine shale develops siliceous shale,mixed shale and argillaceous shale from bottom to top.Besides,lateral distribution of the shale is different from north to south;the shale lithofacies in the north area changes rapidly,the mixed shale in the north area is much thicker than that in the south area,while the siliceous shale in the south area is relatively thicker.Difference in the shale lithofacies is controlled by special sedimentary geologic events;development of the siliceous shale is controlled by the Ordovician-Silurian global volcanic event to some extent,while the mixed shale is significantly influenced by effect of bottom current,and the argillaceous shale is mainly affected by supply of terrestrial clastic material.