The synsedimentary faults and basin-marginal fans located in the central part of the deep-water area of the early Oligocene Qiongdongnan Basin have been investigated using seismic profiles,boreholes,and well-log data....The synsedimentary faults and basin-marginal fans located in the central part of the deep-water area of the early Oligocene Qiongdongnan Basin have been investigated using seismic profiles,boreholes,and well-log data.Through the formations of the characterized paleogeomorphology,such as transverse anticlines,fault ditches,and step-fault belts,the synsedimentary faults are known to have controlled the development position,distribution direction,and extension scales of the basin-marginal fans.For example,at the pitching ends of two adjacent faults,transverse anticlines developed,which controlled the development positions and distributions of the fans.During the early Oligocene,the faults controlled the subsidence center,and fault ditches were formed at the roots of the faults.In the surrounding salient or low salient areas,which were exposed as provenance areas during early Oligocene,the fault ditches acted as the source channels and determined the flow paths of the clastics,where incised valley fills were obviously developed.The fault ditches which developed in the sedimentary basins were able to capture the drainage systems and influenced the distributions of the fans.The large boundary faults and the secondary faults generated two fault terraces and formed step-fault belts.The first fault terrace caused the clastics to be unloaded.As a result,fans were formed at the entrance to the basin.Then,the second fault terrace caused the fans to move forward,with the fans developing in a larger extension scale.The results obtained in this study will potentially be beneficial in the future prospecting activities for reservoirs and coalmeasure source rocks in the basins located in the deep-water areas of the South China Sea.展开更多
At present,researches on the pore evolution of shale reservoir and its evolution mechanism are still at such a groping stage that a consensus has not yet reached.Based on core analysis and thermal simulation experimen...At present,researches on the pore evolution of shale reservoir and its evolution mechanism are still at such a groping stage that a consensus has not yet reached.Based on core analysis and thermal simulation experiments,the pore types,pore structures and pore-size change rules of shale gas reservoirs of Upper Ordovician Wufeng-Lower Silurian Longmaxi Fms in the southeastern(SE)Sichuan Basin and its basin-margin transition zone(hereinafter referred to as the basin-margin transition zone of SE Chongqing)were studied by means of argon ion polishing-scanning electron microscopy(SEM)and atomic force microscopy.Then,the evolution characteristics of organic pores were discussed,and the influence of associated minerals on pore evolution was analyzed.Finally,a pore evolution model for the shale gas reservoirs in this area was established.And the following research results were obtained.First,three types of reservoir spaces are mainly developed in the high-quality shale reservoirs of Wufeng-Longmaxi Fms in this area,including fracture,inorganic pore and organic pore.And the organic pores provide the primary reservoir space of shale gas,which can be divided into four categories,i.e.,amorphous kerogen pores,structured kerogen pores,asphaltene pores and paleontology fossil pores.Second,organic contracted fractures are related to the contraction of organic matters,first appearing on one side of the organic matters and then becomes wider and wider with the increase of temperatures.Third,organic pores are mostly the“spongy”pores distributed densely inside the organic matters.When Ro is in the range of 1.56-3.50%,macropores and mesopores are dominant.And when Ro exceeds 3.50%,macropores decrease while mesopores and micropores increase.Fourth,the types of organic matters and the content of associated minerals(e.g.clay minerals,siliceous particles and pyrite)play an important role in the development of pores.In conclusion,the pore evolution law of Wufeng-Longmaxi shale in the basin-margin transition zone of SE Chongqing is that with the increase of burial depth,inorganic porosity decreases significantly,organic porosity increases first and then decreases,and the total porosity shows a change trend of decreasing first,then increasing and finally decreasing continuously.展开更多
基金The National Natural Science Foundation of China under contract Nos 41872172,41672096 and 41702114the Major National Science and Technology Projects under contract No.2016ZX05026007-004+1 种基金the Natural Science Foundation of Shandong Province under contract No.ZR2019QD008the Natural Science Foundation of Guizhou Province under contract No.20191148
文摘The synsedimentary faults and basin-marginal fans located in the central part of the deep-water area of the early Oligocene Qiongdongnan Basin have been investigated using seismic profiles,boreholes,and well-log data.Through the formations of the characterized paleogeomorphology,such as transverse anticlines,fault ditches,and step-fault belts,the synsedimentary faults are known to have controlled the development position,distribution direction,and extension scales of the basin-marginal fans.For example,at the pitching ends of two adjacent faults,transverse anticlines developed,which controlled the development positions and distributions of the fans.During the early Oligocene,the faults controlled the subsidence center,and fault ditches were formed at the roots of the faults.In the surrounding salient or low salient areas,which were exposed as provenance areas during early Oligocene,the fault ditches acted as the source channels and determined the flow paths of the clastics,where incised valley fills were obviously developed.The fault ditches which developed in the sedimentary basins were able to capture the drainage systems and influenced the distributions of the fans.The large boundary faults and the secondary faults generated two fault terraces and formed step-fault belts.The first fault terrace caused the clastics to be unloaded.As a result,fans were formed at the entrance to the basin.Then,the second fault terrace caused the fans to move forward,with the fans developing in a larger extension scale.The results obtained in this study will potentially be beneficial in the future prospecting activities for reservoirs and coalmeasure source rocks in the basins located in the deep-water areas of the South China Sea.
基金supported by the National Major Science and Technology Project“Demonstration project of normal-pressure shale gas exploration and development in the Pengshui area”(No.2016ZX05061)the Sinopec Science and Technology Development Department Project“Study on main controlling factors of shale gas enrichment in the basin-margin transition zone of SE Chongqing”(No.P18057-2).
文摘At present,researches on the pore evolution of shale reservoir and its evolution mechanism are still at such a groping stage that a consensus has not yet reached.Based on core analysis and thermal simulation experiments,the pore types,pore structures and pore-size change rules of shale gas reservoirs of Upper Ordovician Wufeng-Lower Silurian Longmaxi Fms in the southeastern(SE)Sichuan Basin and its basin-margin transition zone(hereinafter referred to as the basin-margin transition zone of SE Chongqing)were studied by means of argon ion polishing-scanning electron microscopy(SEM)and atomic force microscopy.Then,the evolution characteristics of organic pores were discussed,and the influence of associated minerals on pore evolution was analyzed.Finally,a pore evolution model for the shale gas reservoirs in this area was established.And the following research results were obtained.First,three types of reservoir spaces are mainly developed in the high-quality shale reservoirs of Wufeng-Longmaxi Fms in this area,including fracture,inorganic pore and organic pore.And the organic pores provide the primary reservoir space of shale gas,which can be divided into four categories,i.e.,amorphous kerogen pores,structured kerogen pores,asphaltene pores and paleontology fossil pores.Second,organic contracted fractures are related to the contraction of organic matters,first appearing on one side of the organic matters and then becomes wider and wider with the increase of temperatures.Third,organic pores are mostly the“spongy”pores distributed densely inside the organic matters.When Ro is in the range of 1.56-3.50%,macropores and mesopores are dominant.And when Ro exceeds 3.50%,macropores decrease while mesopores and micropores increase.Fourth,the types of organic matters and the content of associated minerals(e.g.clay minerals,siliceous particles and pyrite)play an important role in the development of pores.In conclusion,the pore evolution law of Wufeng-Longmaxi shale in the basin-margin transition zone of SE Chongqing is that with the increase of burial depth,inorganic porosity decreases significantly,organic porosity increases first and then decreases,and the total porosity shows a change trend of decreasing first,then increasing and finally decreasing continuously.
