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01551 Gas accumulation from oil cracking in the eastern Tarim Basin: a case study of the YN2 gas field
03 Gaseous fuels (sources, properties, recovery, treatment) paste electrode required an optimum carbon nanotubes concentration indicates that low-surface area carbon blacks are good candidates for the dispersion of single wall carbon nanotubes, and that a maximum of 200% increase in charge storage capacity can be obtained from carbon black/SWNT silicon oil composites.
03
GASEOUS FUELS Sources, properties, recovery, treatment
06/01551 Gas accumulation from oil cracking in the eastern Tarim Basin: a case study of the YN2 gas field Zhao, W. et al. Organic Geochemistry, 2005, 36, (12), 1602-1616. Oil and gas exploration in eastern Tarim Basin, NW China has been successful in recent years, with several commercial gas accumulations being discovered in a thermally mature to over-mature region. The Yingnan2 (YN2) gas field, situated in the Yingnan structure of the Yingjisu Depression, produces ~ases that are relatively enriched in nitrogen and C2+ alkanes. The (5 3C1 (-38.6%0 to 36.2%o) and (5 13C2 values (-30.9%0 to 34.7%0) of these gases are characteristic of marine sourced gases with relatively high maturity levels. The distributions of biomarkers in the associated condensates suggest close affinities with the Cambrian-Lower Ordovician source rocks which, in the Yingjisu Sag, are currently over-mature (with 3-4%Ro). Burial and thermal maturity modelling results indicate that paleo-temperatures of the Cambrian-Lower Ordovician source rocks had increased from 90 to 210°C during the late Caledonian orogeny (458-438 Ma), due to rapid subsidence and sediment loading. By the end of Ordovician, hydrocarbon potential in these source rocks had been largely exhausted. The homogenization temperatures of hydrocarbon fluid inclusions identified from the Jurassic reservoirs of the YN2 gas field suggest a hydrocarbon emplacement time as recent as about 10 Ma, when the maturity levels of Middle-Lower Jurassic source rocks in the study area were too low (<0.7%Ro) to form a large quantity of oil and gas. The presence of abundant diamondoid hydrocarbons in the associated condensates and the relatively heavy isotopic values of the oils indicate that the gases were derived from thermal cracking of earlyformed oils. Estimation from the stable carbon isotope ratios of gaseous alkanes suggests that the gases may have been formed at temperatures well above 190°C. Thus, the oil and gas accumulation history in the study area can be reconstructed as follows: (1) during the late Caledonian orogeny, the Cambrian-Lower Ordovician marine source rocks had gone through the peak oil, wet gas and dry gas generation stages, with the generated oil and gas migrating upwards along faults and fractures to form early oil and gas accumulations in the Middle-Upper Ordovician and Silurian sandstone reservoirs; (2) since the late Yanshanian orogeny, the early oil accumulations have been buried deeper and oil has undergone thermal cracking to form gas; (3) during the late Himalayan orogeny, the seals for the deep reservoirs were breached: and the gas and condensates migrated upward and eventually accumulating in the relatively shallow Jurassic reservoirs.
06•01552 Gas systems in the Kuche Depression of the Tarim Basin: source rock distributions, generation kinetics and gas accumulation history Zhao, W. et al. Organic Geochemistry, 2005, 36, (12), 1583 1601. Six petroleum source beds have been developed in the Kuche Depression (also known as 'Kuqa Depression') of the Tarim Basin, including three lacustrine source rocks (Middle and Upper Triassic Kelamayi and Huangshanjie formations, and Middle Jurassic Qiakemake Formation) and three coal measures (Upper Triassic Taliqike Formation, Lower Jurassic Yangxia Formation, and Middle Jurassic Kezilenuer Formation). While type I-II organic matter occurs in the Middle Jurassic Qiakemake Formation (J2q), other source beds contain dominantly type III organic matter. Gas generation rates and stable carbon isotopic kinetics of methane generation from representative source rocks collected in the Kuche Depression were measured and calculated using an on-line dry and open pyrolysis system. Combined with hydrocarbon generation history modelling, the formation and evolution processes of the Jurassic-Triassic highly efficient gas kitchens were established. High sedimentation rate in the Neogene and the fast deposition of the Kuche Formation within the Pliocene (5 Ma) in particular have led to the rapid increase in Mesozoic source rock maturity, resulting in significant dry gas generation. The extremely high gas generation rates from source kitchens have apparently expedited the formation of highly efficient gas accumulations in the
Kuche Depression. Because different Mesozoic source rocks occur in different structural belts, the presence of both lacustrine and coaly gas kitchens during the Cenozoic time can be identified in the Kuche Depression. As shown by the chemical and stable carbon isotope compositions of the discovered gases, the formation of the giant gas pools in the Kela 2, Dina 2, Yaha and Wucan 1 have involved very different geological processes due to the difference in their gas source kitchens.
06/01553 Geochemical characteristics of the Zhaolanzhuang sour gas accumulation and thermochemical sulfate reduction in the Jixian Sag of Bohai Bay Basin Zhang, S. et al. Organic Geochemistry, 2005, 36, (12), 1717-1730. Natural gas from the Zhaolanzhuang field of the Jizhong Superdepression, Bohai Bay Basin contains the highest proportions of H2S (40-92%) among the sour gases encountered in China, The gas payzones include the Eocene-Oligocene Kongdian Formation (Ek) and the Es4 member of the Shahejie Formation. The sedimentary sequence consists of halite, anhydrite, carbonate, sandstone and shale interbeds deposited in the evaporative brackish water lacustrine - salt lake setting. In the deepest part of the Jinxian sag, the total thickness of evaporites is more than 1000 m, of which halite accounts for over 40%. Various organic-rich mudstones intercalated with the evaporites are currently within the conventional hydrocarbon window (with a depth of 2500-3500 m), and likely the source for the oil and sour gas in the Zhaolanzhuang field. The temperatures of the gas reservoirs range from 75 to 100°C, too low for significant thermochemical sulfate reduction. The co-occurrence of abundant elemental sulfur with the sour gas and the (534S values of the various sulfur-containing compounds indicate that the HzS gases were most likely derived from much deeper source kitchens where significant thermochemical sulfate reduction has occurred.
06/01554 Geochemistry and episodic accumulation of natural gases from the Ledong gas field in the Yinggehai Basin, offshore South China Sea Huang, B. et al. Organic Geochemistry, 2005, 36, (12), 1689-1702. The Ledong gas field, consisting of three gas pools in a shale diapir structure zone, is the largest gas discovery in the Yinggehai Basin. The gases produced from the Pliocene and Quaternary marine sandstone reservoirs show a considerable variation in chemical composition, with 5.4-88% CH4, 0-93% COz, and 1-23.7% N~. The CO2-enriched gases often display heavier methane (513C values than those with low CO2 contents. The (515Nvalues of the gases range from - 8 to 2%0,and the N2 content correlates negatively with the CO2 content. The high geothermal gradient associated with a relatively great burial depth in this area has led to the generation of hydrocarbon and nitrogen gases from the Lower-Middle Miocene source rocks and the formation of abundant CO2 from the Tertiary calcareous-shales and pre-Tertiary carbonates. The compositional heterogeneities and stable carbon isotope data of the produced gases indicate that the formation of the LD221 gas field is attributed to three phases of gas migration: initially biogenic gas, followed by thermogenic hydrocarbon gas, and then CO2rich gas. The filling processes occurred within a short period approximately from 1.2 to 0.1 Ma based on the results of the kinetics modelling. Geophysical and geochemical data show that the diapiric faults that cut through Miocene sediments act as the main pathways for upward gas migration from the deep overpressured system into the shallow normal pressure reservoirs, and that the deep overpressure is the main driving force for vertical and lateral migration of the gases. This gas migration pattern implies that the transitional pressure zone around the shale diapir structures was on the pathway of upward migrating gases, and is also a favourable place for gas accumulation. The proposed multiple sources and multiple phases of gas migration and accumulation model for the Ledong gas field potentially provide useful information for the future exploration efforts in this area.
06/01555 Geochemistry and occurrence of inorganic gas accumulations in Chinese sedimentary basins Dai, J. et al. Organic Geochemistry, 2005, 36, (12), 1664 1688. Inorganic gases are commonly seen in eastern China and occasionally in southern China from the shallow water columns above hot and cold springs. The gases contain 68% to nearly 100% CO2, with b13Cco2 and 6a3C1 values in the range of 1.18%o to 6.00%o and -19.48%o to 24.94%o, respectively. All of the 34 large inorganic CO2 and one inorganic methane accumulations discovered in China are distributed in eastern parts of the country, from both onshore and continental shelf basins. No commercial inorganic gas accumulation has been found in central and western China. This is a review of the occurrence and geochemical characteristics of inorganic gas accumulations in Chinese sedimentary basins. A detailed study of gas samples collected from four representative inorganic COz pools and one possible inorganic methane pool indicates that inorganic alkane gases typically show o o 613 C1 values greater than -10%o versus PDB (mostly >-30%o), with a positive stable carbon isotope sequence of 613 C1 < (5T3 C2 < (5] 3 C3 <
Fuel and Energy Abstracts
July 2006
241
03
GASEOUS FUELS Sources, properties, recovery, treatment
06/01551 Gas accumulation from oil cracking in the eastern Tarim Basin: a case study of the YN2 gas field Zhao, W. et al. Organic Geochemistry, 2005, 36, (12), 1602-1616. Oil and gas exploration in eastern Tarim Basin, NW China has been successful in recent years, with several commercial gas accumulations being discovered in a thermally mature to over-mature region. The Yingnan2 (YN2) gas field, situated in the Yingnan structure of the Yingjisu Depression, produces ~ases that are relatively enriched in nitrogen and C2+ alkanes. The (5 3C1 (-38.6%0 to 36.2%o) and (5 13C2 values (-30.9%0 to 34.7%0) of these gases are characteristic of marine sourced gases with relatively high maturity levels. The distributions of biomarkers in the associated condensates suggest close affinities with the Cambrian-Lower Ordovician source rocks which, in the Yingjisu Sag, are currently over-mature (with 3-4%Ro). Burial and thermal maturity modelling results indicate that paleo-temperatures of the Cambrian-Lower Ordovician source rocks had increased from 90 to 210°C during the late Caledonian orogeny (458-438 Ma), due to rapid subsidence and sediment loading. By the end of Ordovician, hydrocarbon potential in these source rocks had been largely exhausted. The homogenization temperatures of hydrocarbon fluid inclusions identified from the Jurassic reservoirs of the YN2 gas field suggest a hydrocarbon emplacement time as recent as about 10 Ma, when the maturity levels of Middle-Lower Jurassic source rocks in the study area were too low (<0.7%Ro) to form a large quantity of oil and gas. The presence of abundant diamondoid hydrocarbons in the associated condensates and the relatively heavy isotopic values of the oils indicate that the gases were derived from thermal cracking of earlyformed oils. Estimation from the stable carbon isotope ratios of gaseous alkanes suggests that the gases may have been formed at temperatures well above 190°C. Thus, the oil and gas accumulation history in the study area can be reconstructed as follows: (1) during the late Caledonian orogeny, the Cambrian-Lower Ordovician marine source rocks had gone through the peak oil, wet gas and dry gas generation stages, with the generated oil and gas migrating upwards along faults and fractures to form early oil and gas accumulations in the Middle-Upper Ordovician and Silurian sandstone reservoirs; (2) since the late Yanshanian orogeny, the early oil accumulations have been buried deeper and oil has undergone thermal cracking to form gas; (3) during the late Himalayan orogeny, the seals for the deep reservoirs were breached: and the gas and condensates migrated upward and eventually accumulating in the relatively shallow Jurassic reservoirs.
06•01552 Gas systems in the Kuche Depression of the Tarim Basin: source rock distributions, generation kinetics and gas accumulation history Zhao, W. et al. Organic Geochemistry, 2005, 36, (12), 1583 1601. Six petroleum source beds have been developed in the Kuche Depression (also known as 'Kuqa Depression') of the Tarim Basin, including three lacustrine source rocks (Middle and Upper Triassic Kelamayi and Huangshanjie formations, and Middle Jurassic Qiakemake Formation) and three coal measures (Upper Triassic Taliqike Formation, Lower Jurassic Yangxia Formation, and Middle Jurassic Kezilenuer Formation). While type I-II organic matter occurs in the Middle Jurassic Qiakemake Formation (J2q), other source beds contain dominantly type III organic matter. Gas generation rates and stable carbon isotopic kinetics of methane generation from representative source rocks collected in the Kuche Depression were measured and calculated using an on-line dry and open pyrolysis system. Combined with hydrocarbon generation history modelling, the formation and evolution processes of the Jurassic-Triassic highly efficient gas kitchens were established. High sedimentation rate in the Neogene and the fast deposition of the Kuche Formation within the Pliocene (5 Ma) in particular have led to the rapid increase in Mesozoic source rock maturity, resulting in significant dry gas generation. The extremely high gas generation rates from source kitchens have apparently expedited the formation of highly efficient gas accumulations in the
Kuche Depression. Because different Mesozoic source rocks occur in different structural belts, the presence of both lacustrine and coaly gas kitchens during the Cenozoic time can be identified in the Kuche Depression. As shown by the chemical and stable carbon isotope compositions of the discovered gases, the formation of the giant gas pools in the Kela 2, Dina 2, Yaha and Wucan 1 have involved very different geological processes due to the difference in their gas source kitchens.
06/01553 Geochemical characteristics of the Zhaolanzhuang sour gas accumulation and thermochemical sulfate reduction in the Jixian Sag of Bohai Bay Basin Zhang, S. et al. Organic Geochemistry, 2005, 36, (12), 1717-1730. Natural gas from the Zhaolanzhuang field of the Jizhong Superdepression, Bohai Bay Basin contains the highest proportions of H2S (40-92%) among the sour gases encountered in China, The gas payzones include the Eocene-Oligocene Kongdian Formation (Ek) and the Es4 member of the Shahejie Formation. The sedimentary sequence consists of halite, anhydrite, carbonate, sandstone and shale interbeds deposited in the evaporative brackish water lacustrine - salt lake setting. In the deepest part of the Jinxian sag, the total thickness of evaporites is more than 1000 m, of which halite accounts for over 40%. Various organic-rich mudstones intercalated with the evaporites are currently within the conventional hydrocarbon window (with a depth of 2500-3500 m), and likely the source for the oil and sour gas in the Zhaolanzhuang field. The temperatures of the gas reservoirs range from 75 to 100°C, too low for significant thermochemical sulfate reduction. The co-occurrence of abundant elemental sulfur with the sour gas and the (534S values of the various sulfur-containing compounds indicate that the HzS gases were most likely derived from much deeper source kitchens where significant thermochemical sulfate reduction has occurred.
06/01554 Geochemistry and episodic accumulation of natural gases from the Ledong gas field in the Yinggehai Basin, offshore South China Sea Huang, B. et al. Organic Geochemistry, 2005, 36, (12), 1689-1702. The Ledong gas field, consisting of three gas pools in a shale diapir structure zone, is the largest gas discovery in the Yinggehai Basin. The gases produced from the Pliocene and Quaternary marine sandstone reservoirs show a considerable variation in chemical composition, with 5.4-88% CH4, 0-93% COz, and 1-23.7% N~. The CO2-enriched gases often display heavier methane (513C values than those with low CO2 contents. The (515Nvalues of the gases range from - 8 to 2%0,and the N2 content correlates negatively with the CO2 content. The high geothermal gradient associated with a relatively great burial depth in this area has led to the generation of hydrocarbon and nitrogen gases from the Lower-Middle Miocene source rocks and the formation of abundant CO2 from the Tertiary calcareous-shales and pre-Tertiary carbonates. The compositional heterogeneities and stable carbon isotope data of the produced gases indicate that the formation of the LD221 gas field is attributed to three phases of gas migration: initially biogenic gas, followed by thermogenic hydrocarbon gas, and then CO2rich gas. The filling processes occurred within a short period approximately from 1.2 to 0.1 Ma based on the results of the kinetics modelling. Geophysical and geochemical data show that the diapiric faults that cut through Miocene sediments act as the main pathways for upward gas migration from the deep overpressured system into the shallow normal pressure reservoirs, and that the deep overpressure is the main driving force for vertical and lateral migration of the gases. This gas migration pattern implies that the transitional pressure zone around the shale diapir structures was on the pathway of upward migrating gases, and is also a favourable place for gas accumulation. The proposed multiple sources and multiple phases of gas migration and accumulation model for the Ledong gas field potentially provide useful information for the future exploration efforts in this area.
06/01555 Geochemistry and occurrence of inorganic gas accumulations in Chinese sedimentary basins Dai, J. et al. Organic Geochemistry, 2005, 36, (12), 1664 1688. Inorganic gases are commonly seen in eastern China and occasionally in southern China from the shallow water columns above hot and cold springs. The gases contain 68% to nearly 100% CO2, with b13Cco2 and 6a3C1 values in the range of 1.18%o to 6.00%o and -19.48%o to 24.94%o, respectively. All of the 34 large inorganic CO2 and one inorganic methane accumulations discovered in China are distributed in eastern parts of the country, from both onshore and continental shelf basins. No commercial inorganic gas accumulation has been found in central and western China. This is a review of the occurrence and geochemical characteristics of inorganic gas accumulations in Chinese sedimentary basins. A detailed study of gas samples collected from four representative inorganic COz pools and one possible inorganic methane pool indicates that inorganic alkane gases typically show o o 613 C1 values greater than -10%o versus PDB (mostly >-30%o), with a positive stable carbon isotope sequence of 613 C1 < (5T3 C2 < (5] 3 C3 <
Fuel and Energy Abstracts
July 2006
241