Abundant organic inclusions are present in the Qinglong antimony deposit. However, the source rocks of these organic matters have not been reliably identified. Recently, a paleo--oil reservoir was found in the Qinglon...Abundant organic inclusions are present in the Qinglong antimony deposit. However, the source rocks of these organic matters have not been reliably identified. Recently, a paleo--oil reservoir was found in the Qinglong antimony deposit. In view of similar components of gaseous hydrocarbon, we propose that the organic matters observed in inclusions in Qinglong antimony deposit would come from this paleo-oil reservoir. We used the Re-Os dating method to determine the age of the bitumen from this paleo-oil reservoir, and obtained an isochron age of 254.3~2.8 Ma. The age indicates that the oil- generation from source rock occurred in the early Late Permian, earlier than the Sb mineralization age （-148~8.5 Ma） in the Qinglong antimony deposit area. After oil generation from Devonian source rock, first and secondary migration, the crude oil have probably entered into the fractures and pores of volcanic rocks and limestone and formed a paleo-oil reservoir in the western wing of Dachang anticline. As burial process deepened, the crude oil has turned into natural gas, migrates into the core of Dachang anticline and formed a paleo-gas reservoir. The hydrocarbons （including CH4） in the reservoirs can serve as reducing agent to provide the sulfur required for Sb mineralization through thermal chemical reduction of sulfates. Therefore, the formation of oil-gas in the area is a prerequisite for the Sb mineralization in the Qinglong antimony deposit.展开更多
Natural bitumen is the evolutionary residue of hydrocarbon of sedimentary organic matter. Several kinds of bitumen with different occurrences, including bitumen in source rock, migration bitumen filled in fault, oil-b...Natural bitumen is the evolutionary residue of hydrocarbon of sedimentary organic matter. Several kinds of bitumen with different occurrences, including bitumen in source rock, migration bitumen filled in fault, oil-bed bitumen and paleo-reservoir bitumen, are distributed widely in the Dabashan foreland. These kinds of bitumen represent the process of oil/gas formation, migration and accumulation in the region. Bitumen in source rock fiUed in fractures and stylolite and experienced deformation simultaneously together with source rock themselves. It indicated that oil/gas generation and expelling from source rock occurred under normal buried thermal conditions during prototype basin evolution stages prior to orogeny. Occurrences of bitumen in source rock indicated that paleo- reservoir formation conditions existed in the Dabashan foreland. Migration bitumen being widespread in the fault revealed that the fault was the main channel for oil/gas migration, which occurred synchronously with Jurassic foreland deformation. Oil-bed bitumen was the kind of pyrolysis bitumen that distributed in solution pores of reservoir rock in the Dabashan foreland depression, the northeastern Sichuan Basin. Geochemistry of oil-bed bitumen indicated that natural gas that accumulated in the Dabashan foreland depression formed from liquid hydrocarbon by pyrolysis process. However, paleo-reservior bitumen in the Dabashan forleland was the kind of degradation bitumen that formed from liquid hydrocarbon within the paleo-reservior by oxidation, alteration and other secondary changes due to paleo-reservior damage during tectonics in the Dabashan foreland. In combination with the tectonic evolution of the Dabashan foreland, it is proposed that the oil/gas generated, migrated and accumulated to form the paleo-reservoir during the Triassic Indosinian tectonic movement. Jurassic collision orogeny, the Yanshan tectonic movement, led to intracontinental orogeny of the Dabashan area accompanied by geofluid expelling and paleo-reservoir damage in the Dabashan foreland. The present work proposed that there is liquid hydrocarbon exploration potential in the Dabashan foreland, while there are prospects for the existence of natural gas in the Dabashan foreland depression.展开更多
Bitumen from the Nanpanjiang Basin occurs mainly in the Middle Devonian and Upper Permian reef limestone paleo-oil reservoirs and reserves primarily in holes and fractures and secondarily in minor matrix pores and bio...Bitumen from the Nanpanjiang Basin occurs mainly in the Middle Devonian and Upper Permian reef limestone paleo-oil reservoirs and reserves primarily in holes and fractures and secondarily in minor matrix pores and bio-cavities. N2 is the main component of the natural gas and is often associated with pyrobitumen in paleo-oil reservoirs. The present study shows that the bitumen in paleo-oil reservoirs was sourced from the Middle Devonian argillaceous source rock and belongs to pyrobitumen by crude oil cracking under high temperature and pressure. But the natural gas with high content of N2 is neither an oil-cracked gas nor a coal-formed gas generated from the Upper Permian Longtan Formation source rock, instead it is a kerogen-cracked gas generated at the late stage from the Middle Devonian argilla- ceous source rock. The crude oil in paleo-oil reservoirs completely cracked into pyrobitumen and methane gas by the agency of hugely thick Triassic deposits. After that, the abnormal high pressure of methane gas reservoirs was completely destroyed due to the erosion of 2000--4500-m-thick Triassic strata. But the kerogen-cracked gas with normal pressure was preserved under the relatively sealed condition and became the main body of the gas shows.展开更多
The Puguang （普光） gas field is the largest gas field found in marine carbonates in China. The Feixianguan （飞仙关） and Changxing （长兴） reservoirs are two such reservoirs that had been buried to a depth of abou...The Puguang （普光） gas field is the largest gas field found in marine carbonates in China. The Feixianguan （飞仙关） and Changxing （长兴） reservoirs are two such reservoirs that had been buried to a depth of about 7 000 m and experienced maximum temperature of up to 220 ℃ before uplift to the present-day depth of 5 000-5 500 m, with present-day thermal maturity between 2.0% and 3.0% equivalent vitrinite reflectance （Ro）. Bitumen staining is ubiquitous throughout the Feixianguan and Changxing formations, with the greatest concentrations in zones with the highest porosity and permeability, suggesting that the solid bitumen is the result of in-situ cracking of oil. According to the distribution of bitumen in the core, the paleo-oil boundary can be approximately determined. The paleo-oil resource is calculated to be about （0.61-0.92） × 10^9 t （average 0.76 × 10^9 t）, and the cracked gas volume is about （380.80-595.80） × 10^9 m^3 （average 488.30 × 10^9 m^3）; at least 58.74% of cracked gas is preserved in Puguang gas field. The study area experienced not only the cracking of oil but also thermochemical sulfate reduction, resulting in large quantities of nonhydrocarbon gas, with about 15.2% H2S and 8.3% CO2, together with the structural reconfiguration. During the whole process, the great change of volume and pressure compels the PVTsim modeling software to simulate various factors, such as the cracking of oil, the thermochemical sulfate reduction （TSR） and the tectonic uplift in both isolated and open geological conditions, respectively. The results show that although any one of these factors may induce greater pressure changes in an isolated system than in a closed system, the oil cracking and C3＋ involving TSR lead to overpressure during the early stage of gas reservoir. Therefore, the tectonic uplift and the methane-dominated TSR, as well as the semi-open system contribute to the reducing pressure resulting in the current normal formation pressure.展开更多
基金financially supported by Natural Science Foundation of China (No.41362007)The Research of Scientific Base of Typical Metal Mineral from the Ministry of Land and Resources (No.20091107)the Research Project on the Metallogenic Regularity of the Typical Strata Controlled Deposits of National Crisis Mines in Southwest China (No.20089943)
文摘Abundant organic inclusions are present in the Qinglong antimony deposit. However, the source rocks of these organic matters have not been reliably identified. Recently, a paleo--oil reservoir was found in the Qinglong antimony deposit. In view of similar components of gaseous hydrocarbon, we propose that the organic matters observed in inclusions in Qinglong antimony deposit would come from this paleo-oil reservoir. We used the Re-Os dating method to determine the age of the bitumen from this paleo-oil reservoir, and obtained an isochron age of 254.3~2.8 Ma. The age indicates that the oil- generation from source rock occurred in the early Late Permian, earlier than the Sb mineralization age （-148~8.5 Ma） in the Qinglong antimony deposit area. After oil generation from Devonian source rock, first and secondary migration, the crude oil have probably entered into the fractures and pores of volcanic rocks and limestone and formed a paleo-oil reservoir in the western wing of Dachang anticline. As burial process deepened, the crude oil has turned into natural gas, migrates into the core of Dachang anticline and formed a paleo-gas reservoir. The hydrocarbons （including CH4） in the reservoirs can serve as reducing agent to provide the sulfur required for Sb mineralization through thermal chemical reduction of sulfates. Therefore, the formation of oil-gas in the area is a prerequisite for the Sb mineralization in the Qinglong antimony deposit.
基金funded by CNSF (No.41173055)and marine department,Sinopec
文摘Natural bitumen is the evolutionary residue of hydrocarbon of sedimentary organic matter. Several kinds of bitumen with different occurrences, including bitumen in source rock, migration bitumen filled in fault, oil-bed bitumen and paleo-reservoir bitumen, are distributed widely in the Dabashan foreland. These kinds of bitumen represent the process of oil/gas formation, migration and accumulation in the region. Bitumen in source rock fiUed in fractures and stylolite and experienced deformation simultaneously together with source rock themselves. It indicated that oil/gas generation and expelling from source rock occurred under normal buried thermal conditions during prototype basin evolution stages prior to orogeny. Occurrences of bitumen in source rock indicated that paleo- reservoir formation conditions existed in the Dabashan foreland. Migration bitumen being widespread in the fault revealed that the fault was the main channel for oil/gas migration, which occurred synchronously with Jurassic foreland deformation. Oil-bed bitumen was the kind of pyrolysis bitumen that distributed in solution pores of reservoir rock in the Dabashan foreland depression, the northeastern Sichuan Basin. Geochemistry of oil-bed bitumen indicated that natural gas that accumulated in the Dabashan foreland depression formed from liquid hydrocarbon by pyrolysis process. However, paleo-reservior bitumen in the Dabashan forleland was the kind of degradation bitumen that formed from liquid hydrocarbon within the paleo-reservior by oxidation, alteration and other secondary changes due to paleo-reservior damage during tectonics in the Dabashan foreland. In combination with the tectonic evolution of the Dabashan foreland, it is proposed that the oil/gas generated, migrated and accumulated to form the paleo-reservoir during the Triassic Indosinian tectonic movement. Jurassic collision orogeny, the Yanshan tectonic movement, led to intracontinental orogeny of the Dabashan area accompanied by geofluid expelling and paleo-reservoir damage in the Dabashan foreland. The present work proposed that there is liquid hydrocarbon exploration potential in the Dabashan foreland, while there are prospects for the existence of natural gas in the Dabashan foreland depression.
基金Supported by the Sinopec Project (Grant No: P00045)the National Science & Technology Project for the 10th Five-Year Plan (Grant No. 2001BA605A-06)
文摘Bitumen from the Nanpanjiang Basin occurs mainly in the Middle Devonian and Upper Permian reef limestone paleo-oil reservoirs and reserves primarily in holes and fractures and secondarily in minor matrix pores and bio-cavities. N2 is the main component of the natural gas and is often associated with pyrobitumen in paleo-oil reservoirs. The present study shows that the bitumen in paleo-oil reservoirs was sourced from the Middle Devonian argillaceous source rock and belongs to pyrobitumen by crude oil cracking under high temperature and pressure. But the natural gas with high content of N2 is neither an oil-cracked gas nor a coal-formed gas generated from the Upper Permian Longtan Formation source rock, instead it is a kerogen-cracked gas generated at the late stage from the Middle Devonian argilla- ceous source rock. The crude oil in paleo-oil reservoirs completely cracked into pyrobitumen and methane gas by the agency of hugely thick Triassic deposits. After that, the abnormal high pressure of methane gas reservoirs was completely destroyed due to the erosion of 2000--4500-m-thick Triassic strata. But the kerogen-cracked gas with normal pressure was preserved under the relatively sealed condition and became the main body of the gas shows.
基金supported by the National Basic Research Program of China (No. 2005CB422105)the National Natural Science Foundation of China (No. 40772089)
文摘The Puguang （普光） gas field is the largest gas field found in marine carbonates in China. The Feixianguan （飞仙关） and Changxing （长兴） reservoirs are two such reservoirs that had been buried to a depth of about 7 000 m and experienced maximum temperature of up to 220 ℃ before uplift to the present-day depth of 5 000-5 500 m, with present-day thermal maturity between 2.0% and 3.0% equivalent vitrinite reflectance （Ro）. Bitumen staining is ubiquitous throughout the Feixianguan and Changxing formations, with the greatest concentrations in zones with the highest porosity and permeability, suggesting that the solid bitumen is the result of in-situ cracking of oil. According to the distribution of bitumen in the core, the paleo-oil boundary can be approximately determined. The paleo-oil resource is calculated to be about （0.61-0.92） × 10^9 t （average 0.76 × 10^9 t）, and the cracked gas volume is about （380.80-595.80） × 10^9 m^3 （average 488.30 × 10^9 m^3）; at least 58.74% of cracked gas is preserved in Puguang gas field. The study area experienced not only the cracking of oil but also thermochemical sulfate reduction, resulting in large quantities of nonhydrocarbon gas, with about 15.2% H2S and 8.3% CO2, together with the structural reconfiguration. During the whole process, the great change of volume and pressure compels the PVTsim modeling software to simulate various factors, such as the cracking of oil, the thermochemical sulfate reduction （TSR） and the tectonic uplift in both isolated and open geological conditions, respectively. The results show that although any one of these factors may induce greater pressure changes in an isolated system than in a closed system, the oil cracking and C3＋ involving TSR lead to overpressure during the early stage of gas reservoir. Therefore, the tectonic uplift and the methane-dominated TSR, as well as the semi-open system contribute to the reducing pressure resulting in the current normal formation pressure.
