Sand-rich tight sandstone reservoirs are potential areas for oil and gas exploration. However, the high ratio of sandstone thickness to that of the strata in the formation poses many challenges and uncertainties to tr...Sand-rich tight sandstone reservoirs are potential areas for oil and gas exploration. However, the high ratio of sandstone thickness to that of the strata in the formation poses many challenges and uncertainties to traditional lithofacies paleogeography mapping. Therefore, the prediction of reservoir sweet spots has remained problematic in the field of petroleum exploration. This study provides new insight into resolving this problem, based on the analyses of depositional characteristics of a typical modern sand-rich formation in a shallow braided river delta of the central Sichuan Basin, China. The varieties of sand-rich strata in the braided river delta environment include primary braided channels,secondary distributary channels and the distribution of sediments is controlled by the successive superposed strata deposited in paleogeomorphic valleys. The primary distributary channels have stronger hydrodynamic forces with higher proportions of coarse sand deposits than the secondary distributary channels. Therefore, lithofacies paleogeography mapping is controlled by the geomorphology, valley locations, and the migration of channels. We reconstructed the paleogeomorphology and valley systems that existed prior to the deposition of the Xujiahe Formation. Following this, rock-electro identification model for coarse skeletal sand bodies was constructed based on coring data. The results suggest that skeletal sand bodies in primary distributary channels occur mainly in the valleys and low-lying areas,whereas secondary distributary channels and fine deposits generally occur in the highland areas. The thickness distribution of skeletal sand bodies and lithofacies paleogeography map indicate a positive correlation in primary distributary channels and reservoir thickness. A significant correlation exists between different sedimentary facies and petrophysical properties. In addition, the degree of reservoir development in different sedimentary facies indicates that the mapping method reliably predicts the distribution of sweet spots. The application and understanding of the mapping method provide a reference for exploring tight sandstone reservoirs on a regional basis.展开更多
Petrographic analysis combined with various techniques, such as thin section identification, petro-physical property testing, mercury penetration, oil testing results, was used to assess basic reservoir characteristic...Petrographic analysis combined with various techniques, such as thin section identification, petro-physical property testing, mercury penetration, oil testing results, was used to assess basic reservoir characteristics of deep strata in Palaeogene in the northern steep slope zone of the Bonan sag, China. The formation mechanisms of high quality reservoirs in deep strata were discussed according to evolution characteristics of paleopressures and paleofluids in geological period. The deep reservoirs have poor physical properties and mainly develop extra-low porosity, extra-low and ultra-low permeability reservoirs. Reservoir spaces mainly consist of secondary pores and overpressure fractures. Early overpressure, early hydrocarbon filling and dissolution by early organic acids are the major formation mechanisms of high quality reservoirs. The conglomerate in inner fan which had a poor primary physical property mainly experienced strong compaction and calcareous matrix recrystallization. The physical properties of the inner fan were poor with weak dissolution because of poor mobility of fluid. The reservoirs mainly are type IV reservoirs and the distribution extends with the burial depth. The braided channel reservoirs in the middle fan had relative good primary physical properties and strong ability to resist compaction which favored the preservation of primary pores. Large amounts of the secondary porosities were created due to dissolution by early organic acids. A series of micro-fractures generated by early overpressures would be important migration pathways for hydrocarbon and organic acids. Furthermore, early overpressures had retarded maturation of organic matters and organic acids which had flowed into reservoirs already and could keep in acid environment for a long time. This process would contribute significantly to reinforcing the dissolution and enhancing the reservoir quality. The braided channel reservoirs were charged with high oil saturation preferentially by early hydrocarbon filling which could inhibit later cementation. Therefore, the braided channel reservoirs develop a great quantity of reservoir spaces with type I, type II and type III reservoirs in the majority in the deep strata. With the burial depth, distributions of type I and type II reservoirs are narrowed and distribution of type III reservoirs decreases first and then extends. The reservoirs both in outer fan and in interdistributary of the middle fan have extremely poor physical properties because of extensive carbonate cementation. The type of the reservoirs mainly is type IV.展开更多
Marine strata in the Jianghan Plain area are widely distributed with a total depth of more than 8,000 m from the Upper Sinian to the Middle Triassic. Six reservoir caprock units, named Z-C2, C2-O, S, D--C, P and T1, c...Marine strata in the Jianghan Plain area are widely distributed with a total depth of more than 8,000 m from the Upper Sinian to the Middle Triassic. Six reservoir caprock units, named Z-C2, C2-O, S, D--C, P and T1, can be identified with each epoch. The geology, stratigraphy, drilling, oil testing and other basic data as well as the measured inclusion and strontium isotope data in the study area are used in the analysis of the formation and evolution process of marine petroliferous reservoirs in the Jianghan Plain area. This study aims to provide a scientific basis for the further exploration of hydrocarbons in the Jianghan Plain and reduce the risks by analyzing the key factors for hydrocarbon accumulation in the marine strata. Our findings show that in the Lower Palaeozoic hydrocarbon reservoir, oil/gas migration and accumulation chiefly occurred in the early period of the Early Yanshanian, and the hydrocarbon reservoir was destroyed in the middle-late period of the Early Yanshanian. In the Lower Triassic-Carboniferous hydrocarbon reservoir, oil/gas migration and accumulation chiefly occurred in the Early Yanshanian, and the hydrocarbon reservoir suffered destruction from the Late Yanshanian to the Early Himalayanian. The preservation conditions of the marine strata in the Jianghan Plain area have been improved since the Late Himalayanian. However, because all source beds have missed the oil/gas generation fastigium and lost the capacity to generate secondary hydrocarbon, no reaccumulation of hydrocarbons can be detected in the study area＇s marine strata. No industrially exploitable oil/gas reservoir has been discovered in the marine strata of Jianghan Plain area since exploration began in 1958. This study confirms that petroliferous reservoirs in the marine strata have been completely destroyed, and that poor preservation conditions are the primary factor leading to unsuccessful hydrocarbon exploration. It is safely concluded that hydrocarbon exploration in the marine strata of the study area is quite risky.展开更多
为了查明贵州织纳煤田三塘向斜内煤层气储层特征,通过露头、录井、测井、试井等资料,开展了室内实验、测井曲线分析等内容综合分析。研究表明,三塘向斜内主要含煤地层为龙潭组,煤层层数多而薄,煤体结构以碎裂煤和原生结构煤为主,主要煤...为了查明贵州织纳煤田三塘向斜内煤层气储层特征,通过露头、录井、测井、试井等资料,开展了室内实验、测井曲线分析等内容综合分析。研究表明,三塘向斜内主要含煤地层为龙潭组,煤层层数多而薄,煤体结构以碎裂煤和原生结构煤为主,主要煤层含气量在8.98~18.05 m^(3)/t,孔隙度在1.47%~7.67%,渗透率在0.027 1~0.21 m D,节理缝连通性较好,微裂缝发育,部分被充填。研究取得的成果对三塘向斜后续煤层气规模化开发时压裂地质选层提供了参考依据,具有一定的指导意义。展开更多
基金financially supported by the “13th Five-Year Plan” National Science and Technology Major Projects(No. 2016ZX05002006-005)the National Natural Science Foundation of China (No. 41502147)the Sichuan Provincial University “nonconventional oil and gas” scientific research and innovation team construction plan
文摘Sand-rich tight sandstone reservoirs are potential areas for oil and gas exploration. However, the high ratio of sandstone thickness to that of the strata in the formation poses many challenges and uncertainties to traditional lithofacies paleogeography mapping. Therefore, the prediction of reservoir sweet spots has remained problematic in the field of petroleum exploration. This study provides new insight into resolving this problem, based on the analyses of depositional characteristics of a typical modern sand-rich formation in a shallow braided river delta of the central Sichuan Basin, China. The varieties of sand-rich strata in the braided river delta environment include primary braided channels,secondary distributary channels and the distribution of sediments is controlled by the successive superposed strata deposited in paleogeomorphic valleys. The primary distributary channels have stronger hydrodynamic forces with higher proportions of coarse sand deposits than the secondary distributary channels. Therefore, lithofacies paleogeography mapping is controlled by the geomorphology, valley locations, and the migration of channels. We reconstructed the paleogeomorphology and valley systems that existed prior to the deposition of the Xujiahe Formation. Following this, rock-electro identification model for coarse skeletal sand bodies was constructed based on coring data. The results suggest that skeletal sand bodies in primary distributary channels occur mainly in the valleys and low-lying areas,whereas secondary distributary channels and fine deposits generally occur in the highland areas. The thickness distribution of skeletal sand bodies and lithofacies paleogeography map indicate a positive correlation in primary distributary channels and reservoir thickness. A significant correlation exists between different sedimentary facies and petrophysical properties. In addition, the degree of reservoir development in different sedimentary facies indicates that the mapping method reliably predicts the distribution of sweet spots. The application and understanding of the mapping method provide a reference for exploring tight sandstone reservoirs on a regional basis.
基金Project(41102058)supported by the National Natural Science Foundation of ChinaProject(2011ZX05006-003)supported by National Oil&Gas Major Project of China+1 种基金Project(U1262203)supported by Key Program for National Natural Science Foundation of ChinaProject(LW140101A)supported by Excellent Doctoral Dissertation Program of China University of Petroleum
文摘Petrographic analysis combined with various techniques, such as thin section identification, petro-physical property testing, mercury penetration, oil testing results, was used to assess basic reservoir characteristics of deep strata in Palaeogene in the northern steep slope zone of the Bonan sag, China. The formation mechanisms of high quality reservoirs in deep strata were discussed according to evolution characteristics of paleopressures and paleofluids in geological period. The deep reservoirs have poor physical properties and mainly develop extra-low porosity, extra-low and ultra-low permeability reservoirs. Reservoir spaces mainly consist of secondary pores and overpressure fractures. Early overpressure, early hydrocarbon filling and dissolution by early organic acids are the major formation mechanisms of high quality reservoirs. The conglomerate in inner fan which had a poor primary physical property mainly experienced strong compaction and calcareous matrix recrystallization. The physical properties of the inner fan were poor with weak dissolution because of poor mobility of fluid. The reservoirs mainly are type IV reservoirs and the distribution extends with the burial depth. The braided channel reservoirs in the middle fan had relative good primary physical properties and strong ability to resist compaction which favored the preservation of primary pores. Large amounts of the secondary porosities were created due to dissolution by early organic acids. A series of micro-fractures generated by early overpressures would be important migration pathways for hydrocarbon and organic acids. Furthermore, early overpressures had retarded maturation of organic matters and organic acids which had flowed into reservoirs already and could keep in acid environment for a long time. This process would contribute significantly to reinforcing the dissolution and enhancing the reservoir quality. The braided channel reservoirs were charged with high oil saturation preferentially by early hydrocarbon filling which could inhibit later cementation. Therefore, the braided channel reservoirs develop a great quantity of reservoir spaces with type I, type II and type III reservoirs in the majority in the deep strata. With the burial depth, distributions of type I and type II reservoirs are narrowed and distribution of type III reservoirs decreases first and then extends. The reservoirs both in outer fan and in interdistributary of the middle fan have extremely poor physical properties because of extensive carbonate cementation. The type of the reservoirs mainly is type IV.
基金the subsidization of a Major Project of Chinese National Programs for Fundamental Research and Development (973 Program, No. 2012CB214805)supported by the Chinese National Natural Science Foundation (No. 41372141)
文摘Marine strata in the Jianghan Plain area are widely distributed with a total depth of more than 8,000 m from the Upper Sinian to the Middle Triassic. Six reservoir caprock units, named Z-C2, C2-O, S, D--C, P and T1, can be identified with each epoch. The geology, stratigraphy, drilling, oil testing and other basic data as well as the measured inclusion and strontium isotope data in the study area are used in the analysis of the formation and evolution process of marine petroliferous reservoirs in the Jianghan Plain area. This study aims to provide a scientific basis for the further exploration of hydrocarbons in the Jianghan Plain and reduce the risks by analyzing the key factors for hydrocarbon accumulation in the marine strata. Our findings show that in the Lower Palaeozoic hydrocarbon reservoir, oil/gas migration and accumulation chiefly occurred in the early period of the Early Yanshanian, and the hydrocarbon reservoir was destroyed in the middle-late period of the Early Yanshanian. In the Lower Triassic-Carboniferous hydrocarbon reservoir, oil/gas migration and accumulation chiefly occurred in the Early Yanshanian, and the hydrocarbon reservoir suffered destruction from the Late Yanshanian to the Early Himalayanian. The preservation conditions of the marine strata in the Jianghan Plain area have been improved since the Late Himalayanian. However, because all source beds have missed the oil/gas generation fastigium and lost the capacity to generate secondary hydrocarbon, no reaccumulation of hydrocarbons can be detected in the study area＇s marine strata. No industrially exploitable oil/gas reservoir has been discovered in the marine strata of Jianghan Plain area since exploration began in 1958. This study confirms that petroliferous reservoirs in the marine strata have been completely destroyed, and that poor preservation conditions are the primary factor leading to unsuccessful hydrocarbon exploration. It is safely concluded that hydrocarbon exploration in the marine strata of the study area is quite risky.
文摘为了查明贵州织纳煤田三塘向斜内煤层气储层特征,通过露头、录井、测井、试井等资料,开展了室内实验、测井曲线分析等内容综合分析。研究表明,三塘向斜内主要含煤地层为龙潭组,煤层层数多而薄,煤体结构以碎裂煤和原生结构煤为主,主要煤层含气量在8.98~18.05 m^(3)/t,孔隙度在1.47%~7.67%,渗透率在0.027 1~0.21 m D,节理缝连通性较好,微裂缝发育,部分被充填。研究取得的成果对三塘向斜后续煤层气规模化开发时压裂地质选层提供了参考依据,具有一定的指导意义。
