In recent years,a series of highly saturated leakage-type gas hydrates have been discovered in the western Qiongdongnan Basin(QDNB),South China Sea.Based on the molecular compositional and isotopic characteristics of ...In recent years,a series of highly saturated leakage-type gas hydrates have been discovered in the western Qiongdongnan Basin(QDNB),South China Sea.Based on the molecular compositional and isotopic characteristics of the gas samples relevant to the gas hydrates collected from the two leakage-type gas hydrate accumulations in the GMGS5 and GMGS6 drilling zones,a detailed geochemical gas-to-gas correlation was conducted in this study,in order to further understand the geochemical characteristics and possible hydrocarbon sources of these gas hydrates.The natural gas relevant to the gas hydrates in the GMGS5 block is characterized by wet gas(67.96%<%C_(1)<98.58%,C_(1)/C_(1+)<0.9)and significant molecular and carbon isotope fractionation within the depth profile,whereas the gas samples from the GMGS6 block exhibit the characteristics of dry gas(99.25%<%C_(1)<99.81%,C_(1)/C_(1+)>0.9)and lack molecular and carbon isotope fractionation.Approximately 40%‒60%of the methane within the gas hydrate is of microbial origin,while the C^(2+)gas components are typical coal-type gas that are derived from thermogenic source rocks or deeply-buried natural gas fields.In addition,typical in situ primary microbial methane(−80.6‰<δ^(13)C-C_(1)<−67.7‰)was discovered in well W b,which was applied to estimate the contribution of the microbial gas to the gas hydrates.The gas-to-gas correlation results show that the hydrate gases within the two leakage-type gas hydrate accumulations in the GMGS5 and GMGS6 blocks are geochemically different,suggesting that they may have been derived from different source kitchens.Our results further indicate that the deeply-buried thermogenic gas significantly contributed to the shallowly-buried gas hydrates in the western QDNB and multiple effective thermogenic source kitchens provided the hydrocarbon gas in the gas hydrate accumulations.展开更多
The Permian Dalong Formation(P2d) source rocks from the mature Guangyuan outcrop section and the overmature Wangcang outcrop section in Sichuan Basin were selected.The Soxhlet extraction and kerogen catalytic HyPy wer...The Permian Dalong Formation(P2d) source rocks from the mature Guangyuan outcrop section and the overmature Wangcang outcrop section in Sichuan Basin were selected.The Soxhlet extraction and kerogen catalytic HyPy were conducted on the P2d source rocks.The biomarkers obtained by both methods were compared to discuss their difference and the influence extent of thermal maturation on covalently bound biomarkers.The results show that covalently bound biomarkers can hardly be correlated to the corresponding free biomarkers due to severe thermal alterations and/or interference of migrated hydrocarbons in both outcrop sections and thermal maturation have much lower influence on covalently bound biomarkers in kerogens than on free biomarkers in Soxhlet extracts.The application of HyPy in study of biomarker geochemistry can reduce the thermal maturation effect on biomarkers(Ro≤2.4%) to a greater extent and the interference of migrated hydrocarbons between interbedded layers.The covalently bound biomarkers released by HyPy are useful in the study of biomarker geochemistry and oil-source correlation on high-overmature source rocks.展开更多
基金funded by the Key Special Project for Introduced Talents Team of the Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(Grant No.GML2019ZD0102)the Chinese Geological Survey Project(Grant No.DD20190230 and DD20220224)。
文摘In recent years,a series of highly saturated leakage-type gas hydrates have been discovered in the western Qiongdongnan Basin(QDNB),South China Sea.Based on the molecular compositional and isotopic characteristics of the gas samples relevant to the gas hydrates collected from the two leakage-type gas hydrate accumulations in the GMGS5 and GMGS6 drilling zones,a detailed geochemical gas-to-gas correlation was conducted in this study,in order to further understand the geochemical characteristics and possible hydrocarbon sources of these gas hydrates.The natural gas relevant to the gas hydrates in the GMGS5 block is characterized by wet gas(67.96%<%C_(1)<98.58%,C_(1)/C_(1+)<0.9)and significant molecular and carbon isotope fractionation within the depth profile,whereas the gas samples from the GMGS6 block exhibit the characteristics of dry gas(99.25%<%C_(1)<99.81%,C_(1)/C_(1+)>0.9)and lack molecular and carbon isotope fractionation.Approximately 40%‒60%of the methane within the gas hydrate is of microbial origin,while the C^(2+)gas components are typical coal-type gas that are derived from thermogenic source rocks or deeply-buried natural gas fields.In addition,typical in situ primary microbial methane(−80.6‰<δ^(13)C-C_(1)<−67.7‰)was discovered in well W b,which was applied to estimate the contribution of the microbial gas to the gas hydrates.The gas-to-gas correlation results show that the hydrate gases within the two leakage-type gas hydrate accumulations in the GMGS5 and GMGS6 blocks are geochemically different,suggesting that they may have been derived from different source kitchens.Our results further indicate that the deeply-buried thermogenic gas significantly contributed to the shallowly-buried gas hydrates in the western QDNB and multiple effective thermogenic source kitchens provided the hydrocarbon gas in the gas hydrate accumulations.
基金supported by the National Science and Technology Major Project(2011ZX05008-002 and 2011ZX05005-001)
文摘The Permian Dalong Formation(P2d) source rocks from the mature Guangyuan outcrop section and the overmature Wangcang outcrop section in Sichuan Basin were selected.The Soxhlet extraction and kerogen catalytic HyPy were conducted on the P2d source rocks.The biomarkers obtained by both methods were compared to discuss their difference and the influence extent of thermal maturation on covalently bound biomarkers.The results show that covalently bound biomarkers can hardly be correlated to the corresponding free biomarkers due to severe thermal alterations and/or interference of migrated hydrocarbons in both outcrop sections and thermal maturation have much lower influence on covalently bound biomarkers in kerogens than on free biomarkers in Soxhlet extracts.The application of HyPy in study of biomarker geochemistry can reduce the thermal maturation effect on biomarkers(Ro≤2.4%) to a greater extent and the interference of migrated hydrocarbons between interbedded layers.The covalently bound biomarkers released by HyPy are useful in the study of biomarker geochemistry and oil-source correlation on high-overmature source rocks.
