Fault formation and evolution in the presence of multiple pre-existing weaknesses has not been investigated extensively in rift basins. The fault systems of Weixinan Sag, Beibuwan Basin of China, which is fully covere...Fault formation and evolution in the presence of multiple pre-existing weaknesses has not been investigated extensively in rift basins. The fault systems of Weixinan Sag, Beibuwan Basin of China, which is fully covered with high-precision 3-D seismic data and is rich in oil-gas resources, have been successfully reproduced by sandbox modeling in this study with inclusion of multiple pre-existing weaknesses in the experimental model. The basic characteristics of fault formation and evolution revealed by sandbox modeling are as follows. 1） Weakness-reactivation faults and weakness-related faults are formed much earlier than the distant-weakness faults （faults far away from and with little or no relationship to the weakness）. 2） Weakness-reactivation faults and weakness-related faults develop mainly along or parallel to a pre-existing weakness, while distant-weakness faults develop nearly perpendicular to the extension direction. A complicated fault system can be formed in a fixed direction of extension with the existence of multiple pre-existing weaknesses, and the complicated fault system in the Weixinan Sag formed gradually in a nearly N-S direction with multiple pre-existing weaknesses. 3） The increase in the length and number of faults is closely tied to the nature of pre-existing weaknesses. The sandbox model may provide a new clue to detailed fault system research for oil and gas exploration in rift basins.展开更多
Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin.To determine the source and accumulation mode of this crude oil,12 crude oil samples and 27 source rock samp...Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin.To determine the source and accumulation mode of this crude oil,12 crude oil samples and 27 source rock samples were collected and an extensive organic geochemical analysis was conducted on them.Based on the geological conditions and the analytical results,the types,origins and accumulation patterns of crude oil in the study area were elucidated.Except for a shallowly-buried and biodegraded crude oil deposit in Neogene rocks,the crude oil samples in the study area were normal.All of the crude oils were derived from lacustrine source rocks.According to biomarker compositions,the crude oils could be divided into two families,A and B,distinctions that were reinforced by differences in carbon isotope composition and spatial distribution.Oil-source correlation analysis based on biomarkers revealed that Family A oils were derived from the mature oil shale at the bottom of the second member of the Liushagang Formation,while the Family B oils formed in the mature shale of the Liushagang Formation.The Family A oils,generated by oil shale,mainly migrated laterally along sand bodies and were then redistributed in adjacent reservoirs above and below the oil shale layer,as well as in shallow layers at high structural positions,occupying a wide distribution range.The Family B oils were generated by other shale units before migrating vertically along faults to form reservoirs nearby,resulting in a narrow distribution range.展开更多
基金supported by China National Major Project of Oil and Gas (2011ZX05023-004-012, 2011ZX05006-006-02-01)China Natural Science Foundation (Grant No. 40772086)
文摘Fault formation and evolution in the presence of multiple pre-existing weaknesses has not been investigated extensively in rift basins. The fault systems of Weixinan Sag, Beibuwan Basin of China, which is fully covered with high-precision 3-D seismic data and is rich in oil-gas resources, have been successfully reproduced by sandbox modeling in this study with inclusion of multiple pre-existing weaknesses in the experimental model. The basic characteristics of fault formation and evolution revealed by sandbox modeling are as follows. 1） Weakness-reactivation faults and weakness-related faults are formed much earlier than the distant-weakness faults （faults far away from and with little or no relationship to the weakness）. 2） Weakness-reactivation faults and weakness-related faults develop mainly along or parallel to a pre-existing weakness, while distant-weakness faults develop nearly perpendicular to the extension direction. A complicated fault system can be formed in a fixed direction of extension with the existence of multiple pre-existing weaknesses, and the complicated fault system in the Weixinan Sag formed gradually in a nearly N-S direction with multiple pre-existing weaknesses. 3） The increase in the length and number of faults is closely tied to the nature of pre-existing weaknesses. The sandbox model may provide a new clue to detailed fault system research for oil and gas exploration in rift basins.
文摘Crude oil has been discovered in the Paleogene and Neogene units of the Weixinan Sag in the Beibu Gulf Basin.To determine the source and accumulation mode of this crude oil,12 crude oil samples and 27 source rock samples were collected and an extensive organic geochemical analysis was conducted on them.Based on the geological conditions and the analytical results,the types,origins and accumulation patterns of crude oil in the study area were elucidated.Except for a shallowly-buried and biodegraded crude oil deposit in Neogene rocks,the crude oil samples in the study area were normal.All of the crude oils were derived from lacustrine source rocks.According to biomarker compositions,the crude oils could be divided into two families,A and B,distinctions that were reinforced by differences in carbon isotope composition and spatial distribution.Oil-source correlation analysis based on biomarkers revealed that Family A oils were derived from the mature oil shale at the bottom of the second member of the Liushagang Formation,while the Family B oils formed in the mature shale of the Liushagang Formation.The Family A oils,generated by oil shale,mainly migrated laterally along sand bodies and were then redistributed in adjacent reservoirs above and below the oil shale layer,as well as in shallow layers at high structural positions,occupying a wide distribution range.The Family B oils were generated by other shale units before migrating vertically along faults to form reservoirs nearby,resulting in a narrow distribution range.
