In the Triassic Yanchang Formation, Jiyuan-Wuqi area, Ordos Basin, the Chang 6 reservoir is contacted to the Chang 7 high-quality source rock, but the oil pools are unevenly distributed, and complex in oil and water d...In the Triassic Yanchang Formation, Jiyuan-Wuqi area, Ordos Basin, the Chang 6 reservoir is contacted to the Chang 7 high-quality source rock, but the oil pools are unevenly distributed, and complex in oil and water distribution. Through cores observation and fracture statistics, combined with comprehensive analyses of physical property, mercury injection, logging and geochemical data, and comparisons of the sandbodies scales, reservoir physical properties, argillaceous laminae and fractures between source and reservoir in the eastern and western oil-bearing areas and in the central water producing area, it is found that the hydrocarbon accumulation patterns are different in the eastern, central and western areas, and the characteristics of hydrocarbon migration under the background of double-provenance were sorted out. The study results show that the crude oil in the eastern area has different Pr/Ph and sterane distribution from that in the western area. The oil and gas primarily migrated vertically. The high-quality source rocks and favorable source-reservoir-cap combinations lay the foundation for large-scale oil and gas accumulations. Vertically, the oil and gas enrichment is controlled by the scale of sandbody and the difference of physical properties, while on the plane, it is controlled by the connectivity of sandbodies, the argillaceous laminae between source rock and reservoir, the reservoir physical property and the fractures. The sandbodies of oil-rich zones in the eastern and western areas have large thickness, low shale content, good physical properties, weak heterogeneity, few argillaceous laminae and abundant fractures, all of which are favorable for the vertical migration and accumulation of oil and gas. In contrast, in the middle area with converging provenances, the reservoirs, composed of thin sandbodies, features rapid variation in lithology and physical properties, strong heterogeneity, poor continuity of sandbodies, abundant argillaceous laminae between source rock and reservoir, and few fractures, makes it difficult for the oil and gas to migrate vertically, and results in low oil enrichment degree ultimately. For the exploration of continental multiple-provenance tight reservoirs, not only the good-property source rocks and reservoirs, but more importantly the source-reservoir contact relationship and the effect of fractures on the hydrocarbon migration and accumulation should be considered.展开更多
The Chang 6 reservoir of Yanchang formation in Jingan oilfield has relatively poor quality:the porosity ranges mainly from 8 to 14%,and permeability ranges from 0.018 to 10.48 md,with a mean of 1.10 md,categorized as ...The Chang 6 reservoir of Yanchang formation in Jingan oilfield has relatively poor quality:the porosity ranges mainly from 8 to 14%,and permeability ranges from 0.018 to 10.48 md,with a mean of 1.10 md,categorized as low porosity and low permeability reservoir type with strong heterogeneity.Petrographic and geochemical analyses of various components in these sandstones have provided clues of diagenesis.The sandstones at the early stage of diagenesis are characterized by non-ferroan calcite cementation,grain-coating,pore-lining clay minerals,and initial dissolution of detrital grains.Authigenic quartz,porefilling and grain-replacive laumontites,albitized detrital plagioclase,authigenic K-feldspar,illite and late ferroan calcite cement dominate the late diagenesis.Reservoir quality is influenced by products of late diagenesis stage,the cement(calcite,albite,quartz,illite,and laumontite)occluded primary and secondary porosity.The organic acidic fluid derived from organic matter in the source rocks during the late diagenesis,which results in the dissolution of detrital plagioclase and laumontite cement and was the main reason for the enhancement of reservoir-quality.As a result of that,the residual primary pore and dissolution pore comprised the main accumulation space for oil and gas,and thus become important targets for hydrocarbon exploration.展开更多
基金Supported by the National Natural Science Foundation of China(41872165,41572137)
文摘In the Triassic Yanchang Formation, Jiyuan-Wuqi area, Ordos Basin, the Chang 6 reservoir is contacted to the Chang 7 high-quality source rock, but the oil pools are unevenly distributed, and complex in oil and water distribution. Through cores observation and fracture statistics, combined with comprehensive analyses of physical property, mercury injection, logging and geochemical data, and comparisons of the sandbodies scales, reservoir physical properties, argillaceous laminae and fractures between source and reservoir in the eastern and western oil-bearing areas and in the central water producing area, it is found that the hydrocarbon accumulation patterns are different in the eastern, central and western areas, and the characteristics of hydrocarbon migration under the background of double-provenance were sorted out. The study results show that the crude oil in the eastern area has different Pr/Ph and sterane distribution from that in the western area. The oil and gas primarily migrated vertically. The high-quality source rocks and favorable source-reservoir-cap combinations lay the foundation for large-scale oil and gas accumulations. Vertically, the oil and gas enrichment is controlled by the scale of sandbody and the difference of physical properties, while on the plane, it is controlled by the connectivity of sandbodies, the argillaceous laminae between source rock and reservoir, the reservoir physical property and the fractures. The sandbodies of oil-rich zones in the eastern and western areas have large thickness, low shale content, good physical properties, weak heterogeneity, few argillaceous laminae and abundant fractures, all of which are favorable for the vertical migration and accumulation of oil and gas. In contrast, in the middle area with converging provenances, the reservoirs, composed of thin sandbodies, features rapid variation in lithology and physical properties, strong heterogeneity, poor continuity of sandbodies, abundant argillaceous laminae between source rock and reservoir, and few fractures, makes it difficult for the oil and gas to migrate vertically, and results in low oil enrichment degree ultimately. For the exploration of continental multiple-provenance tight reservoirs, not only the good-property source rocks and reservoirs, but more importantly the source-reservoir contact relationship and the effect of fractures on the hydrocarbon migration and accumulation should be considered.
基金The work was supported by China National Petroleum Company(2010D-5006-0103)funded by State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(PLN201616)Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education(TPR-2013-16).We are grateful to the Core analysis Unit at the Chengdu Institute of Sedimentology and Mineralogy.We thank the Stable Isotope Unit at the Central Laboratory of Changqing Oilfield.We thank Zhao Jingzhe,the director of exploration and development,Liu Lili andWei Liping,for assistance with collecting materials and valuable discussions,and Zheng Guanghui for assistance with our field work.The manuscript also benefited from suggestions by Wang Qi,a research scientist at Lanzhou Institute of Geology.
文摘The Chang 6 reservoir of Yanchang formation in Jingan oilfield has relatively poor quality:the porosity ranges mainly from 8 to 14%,and permeability ranges from 0.018 to 10.48 md,with a mean of 1.10 md,categorized as low porosity and low permeability reservoir type with strong heterogeneity.Petrographic and geochemical analyses of various components in these sandstones have provided clues of diagenesis.The sandstones at the early stage of diagenesis are characterized by non-ferroan calcite cementation,grain-coating,pore-lining clay minerals,and initial dissolution of detrital grains.Authigenic quartz,porefilling and grain-replacive laumontites,albitized detrital plagioclase,authigenic K-feldspar,illite and late ferroan calcite cement dominate the late diagenesis.Reservoir quality is influenced by products of late diagenesis stage,the cement(calcite,albite,quartz,illite,and laumontite)occluded primary and secondary porosity.The organic acidic fluid derived from organic matter in the source rocks during the late diagenesis,which results in the dissolution of detrital plagioclase and laumontite cement and was the main reason for the enhancement of reservoir-quality.As a result of that,the residual primary pore and dissolution pore comprised the main accumulation space for oil and gas,and thus become important targets for hydrocarbon exploration.
