To clarify the main enrichment-controlling factors and accumulation mechanisms of shale gas in the Permian Dalong Formation within the Western Hubei-Eastern Chongqing complex structural zone,this study systematically ...To clarify the main enrichment-controlling factors and accumulation mechanisms of shale gas in the Permian Dalong Formation within the Western Hubei-Eastern Chongqing complex structural zone,this study systematically reveals the enrichment patterns and accumulation model through analysis of typical drilling data,geochemical testing,scanning electron microscopy(SEM),methane isothermal adsorption experiments,numerical simulations,and research on tectonic evolution and preservation condition.The results are obtained in two aspects.First,the enrichment of shale gas in the Dalong Formation is synergistically controlled by four factors,i.e.rift troughs controlling shale development,provenance controlling reservoir heterogeneity,temperature and pressure controlling gas occurrence,and structure controlling differential enrichment.The geometry and scale of rift troughs(Chengkou-Western Hubei,and Kaijiang-Liangping)determine the development of organic-rich shale(average TOC>6%,thickness of 15-50 m).Multi-source materials lead to strong heterogeneity of the reservoir,with endogenous minerals as the main component(accounting for 74.31%),and the pores mainly organic matter pores(micropores and mesopores accounting for 93.4%).The formation temperature and pressure control the occurrence state of shale gas,with adsorbed gas(higher than 50%)dominantly in 500-2750 m depth,while free gas(higher than 50%)prevailing at depth deeper than 2750 m depth.The uplift,erosion,and fault systems associated with the Yanshanian tectonic activity result in differential enrichment of shale gas,with three structural styles—broad gentle anticlines,residual synclines,and low gentle slopes—exhibiting relatively high shale gas enrichment.Second,the self-sealing mechanism of medium-shallow shale gas in the Western Hubei-Eastern Chongqing complex structural zone is revealed.Specifically,the Dalong Formation shale aquifer forms a lateral seal for shale gas in the downdip direction via water films and capillary forces,and it combines with the overlying Daye Formation limestone and underlying Xiayao Formation tight layers to establish a synclinal/monoclinal self-sealing accumulation model.The geological insights,such as“four-factor synergistic control”and self-sealing accumulation model,provide a dynamic coupling evaluation framework for shale gas in complex structural zones,promoting the transition of shale gas exploration and evaluation from static descriptions to integrated reservoir-tectonic-fluid analysis.展开更多
The western Hubei-eastern Chongqing area is an important prospective zone for oil and gas exploration in the central Yangtze area. Three representative structures, the Xinchang structure, Longjuba gas-bearing structur...The western Hubei-eastern Chongqing area is an important prospective zone for oil and gas exploration in the central Yangtze area. Three representative structures, the Xinchang structure, Longjuba gas-bearing structure and the Jiannan gas field, were selected to analyze biomarker parameters in marine strata and to examine various types of natural gas and hydrocarbon sources. Fluid inclusions; carbon, oxygen, and strontium isotopic characteristics; organic geochemical analysis and simulation of hydrocarbon generation and expulsion history of source rocks were used for tracing fluid migration paths in marine strata of the study area. The Carboniferous-Triassic reservoirs in three typical structures all experienced at least two stages of fluid accumulation. All marine strata above the early Permian were shown to have fluids originating in the Permian rocks, which differed from the late stage fluids. The fluids accumulated in the late Permian reservoirs of the Xinchang structure were Cambrian fluids, while those in the late Carboniferous reservoirs were sourced from a combination of Silurian and Cambrian fluids. A long-distance and large-scale cross-formational flow of fluids destroyed the preservation conditions of earlier accumulated hydrocarbons. A short-distance cross-formational accumulation of Silurian fluids was shown in the late Permian reservoirs of the Longjuba structure with favorable hydrocarbon preservation conditions. The fluid accumulation in the Carboniferous reservoirs of the Jiannan structure mainly originated from neighboring Silurian strata with a small amount from the Cambrian strata. As a result, the Jiannan structure was determined to have the best preservation conditions of the three. Comparative analysis of fluid migration paths in the three structures revealed that the zone with a weaker late tectonism and no superimposition and modification of the Upper and Lower Paleozoic fluids or the Upper Paleozoic zone with the fluid charging from the Lower Paleozoic in the western Hubei-easteru Chongqing area are important target areas for future exploration.展开更多
基金Supported by the National Natural Science Foundation of China(42472210)Project of the China Geological Survey(DD20221653,DD20230043).
文摘To clarify the main enrichment-controlling factors and accumulation mechanisms of shale gas in the Permian Dalong Formation within the Western Hubei-Eastern Chongqing complex structural zone,this study systematically reveals the enrichment patterns and accumulation model through analysis of typical drilling data,geochemical testing,scanning electron microscopy(SEM),methane isothermal adsorption experiments,numerical simulations,and research on tectonic evolution and preservation condition.The results are obtained in two aspects.First,the enrichment of shale gas in the Dalong Formation is synergistically controlled by four factors,i.e.rift troughs controlling shale development,provenance controlling reservoir heterogeneity,temperature and pressure controlling gas occurrence,and structure controlling differential enrichment.The geometry and scale of rift troughs(Chengkou-Western Hubei,and Kaijiang-Liangping)determine the development of organic-rich shale(average TOC>6%,thickness of 15-50 m).Multi-source materials lead to strong heterogeneity of the reservoir,with endogenous minerals as the main component(accounting for 74.31%),and the pores mainly organic matter pores(micropores and mesopores accounting for 93.4%).The formation temperature and pressure control the occurrence state of shale gas,with adsorbed gas(higher than 50%)dominantly in 500-2750 m depth,while free gas(higher than 50%)prevailing at depth deeper than 2750 m depth.The uplift,erosion,and fault systems associated with the Yanshanian tectonic activity result in differential enrichment of shale gas,with three structural styles—broad gentle anticlines,residual synclines,and low gentle slopes—exhibiting relatively high shale gas enrichment.Second,the self-sealing mechanism of medium-shallow shale gas in the Western Hubei-Eastern Chongqing complex structural zone is revealed.Specifically,the Dalong Formation shale aquifer forms a lateral seal for shale gas in the downdip direction via water films and capillary forces,and it combines with the overlying Daye Formation limestone and underlying Xiayao Formation tight layers to establish a synclinal/monoclinal self-sealing accumulation model.The geological insights,such as“four-factor synergistic control”and self-sealing accumulation model,provide a dynamic coupling evaluation framework for shale gas in complex structural zones,promoting the transition of shale gas exploration and evaluation from static descriptions to integrated reservoir-tectonic-fluid analysis.
基金sponsored by National Programs for Fundamental Research and Development (973 Program,2012CB214805)the National Natural Science Foundation (40930424)
文摘The western Hubei-eastern Chongqing area is an important prospective zone for oil and gas exploration in the central Yangtze area. Three representative structures, the Xinchang structure, Longjuba gas-bearing structure and the Jiannan gas field, were selected to analyze biomarker parameters in marine strata and to examine various types of natural gas and hydrocarbon sources. Fluid inclusions; carbon, oxygen, and strontium isotopic characteristics; organic geochemical analysis and simulation of hydrocarbon generation and expulsion history of source rocks were used for tracing fluid migration paths in marine strata of the study area. The Carboniferous-Triassic reservoirs in three typical structures all experienced at least two stages of fluid accumulation. All marine strata above the early Permian were shown to have fluids originating in the Permian rocks, which differed from the late stage fluids. The fluids accumulated in the late Permian reservoirs of the Xinchang structure were Cambrian fluids, while those in the late Carboniferous reservoirs were sourced from a combination of Silurian and Cambrian fluids. A long-distance and large-scale cross-formational flow of fluids destroyed the preservation conditions of earlier accumulated hydrocarbons. A short-distance cross-formational accumulation of Silurian fluids was shown in the late Permian reservoirs of the Longjuba structure with favorable hydrocarbon preservation conditions. The fluid accumulation in the Carboniferous reservoirs of the Jiannan structure mainly originated from neighboring Silurian strata with a small amount from the Cambrian strata. As a result, the Jiannan structure was determined to have the best preservation conditions of the three. Comparative analysis of fluid migration paths in the three structures revealed that the zone with a weaker late tectonism and no superimposition and modification of the Upper and Lower Paleozoic fluids or the Upper Paleozoic zone with the fluid charging from the Lower Paleozoic in the western Hubei-easteru Chongqing area are important target areas for future exploration.
文摘鄂西渝东地区是中国南方海相油气勘探的重要区块,又是目前页岩气勘探的热门地区,该地区晚燕山-喜马拉雅期以来长期遭受隆升剥蚀.剥蚀量是烃源岩热演化、油气藏形成与演化、资源量计算和盆地模拟中不可缺少的基础参数.考虑到剥蚀量恢复方法固有的局限性和适用条件,本文在分析了古温标镜质体反射率Ro剖面特征之后,采用古地温梯度反演法进行钻井剥蚀量恢复,然后分析钻井剥蚀量与钻井开孔层位之间的相关性,再与地质图相结合编制剥蚀量平面分布图.结果表明：鄂西渝东地区古温标Ro剖面不存在明显的＂错断＂、＂跳跃＂现象。记录的古地温为达到最大埋深时的古地温;钻井剥蚀量与钻井开孔层位之间具有明显的相关性,开孔层位越老,剥蚀量越大,反之亦然;晚燕山—喜马拉雅期剥蚀量总体上从东往西逐渐变小.东部的利川复向斜剥蚀量为2000-4000 m,中部的石柱复向斜为1500-2500 m,方斗山以西为1000-1500 m.
