Deep carbonate reservoirs affected by prominent strike-slip faults represent crucial targets in oil and gas exploration owing to their immense resource potential.However,the complex geological environments and poorly ...Deep carbonate reservoirs affected by prominent strike-slip faults represent crucial targets in oil and gas exploration owing to their immense resource potential.However,the complex geological environments and poorly understood histories of the associated paleo-fluid activity have hindered the development of robust theories regarding pore formation and preservation mechanisms,resulting in suboptimal exploration strategies.Leveraging the extensive well deployment by the China Sinopec Group in the Shunbei area of the Tarim Basin,this study addresses these challenges by establishing a comprehensive framework for the evolution of diagenetic fluids within the Middle-Lower Ordovician carbonate formations.Using core samples,thin-section analysis,and cathodoluminescence observations,this study employs high-resolution geochemical methodologies,including isotopic analyses,rare earth element profiling,fluid inclusion studies,and uranium-lead dating,as primary tools for identifying and interpreting paleo-fluid characteristics across various rock types and calcite cement varieties within this stratigraphic interval.The findings reveal several key insights:(i)both RFC and C1 cements are derived from seawater,with C1 forming under burial conditions;(ii)C2,C3,and VC cements result from distinct tectonic events,specifically during the first and third episodes of the Middle Caledonian movement,with meteoric water infiltrating fault systems independently of orogenic belts or paleo-karst systems;and(iii)previous conclusions are challenged,as the influence of hydrothermal activity in this area is found to be minimal.Furthermore,the model presented here serves as a valuable reference for understanding fluid activity events at distal locations within orogenic belts under compressive stress,while accurately capturing fluid variations over different temporal scales within fault zones plays a decisive role.展开更多
The studies on the paleo-fluid in the OrdovicianeSilurian detachment zone in the MiddleeUpper Yangtze area focus on the origin of highdensity methane inclusions and the evolution process of formation pressure,but rare...The studies on the paleo-fluid in the OrdovicianeSilurian detachment zone in the MiddleeUpper Yangtze area focus on the origin of highdensity methane inclusions and the evolution process of formation pressure,but rarely deal with the significance of paleo-fluid to shale gas preservation.In this paper,the relationship between fracture formation and detachment zone was analyzed by observing the OrdovicianeSilurian outcrops in western HunaneHubei area and by investigating the geological characteristics of fracture veins in the drilling cores.Then,the significance of paleo-fluid forming environment and detachment zone to shale gas preservation was studied by using inclusion compositions of fracture veins and homogenization temperature test data.Finally,accumulationedispersion modes of shale gas in the detachment zone were established.The following results were obtained.First,the detachment zone is lithologically composed of silicite with intercalated shale at the OrdovicianeSilurian interface.In the detachment zone,rocks are broken and small crumples are developed.The conjugate-vertical joints are relatively developed in the silicite above and below the detachment zone.Second,multi-stage and multi-type inclusions,especially the aqueous inclusions,are developed in the veins of the detachment zone.Third,the infiltration depth of ancient meteoric water along the detachment zone in the study area is over 4000 m.High-density overpressure methane inclusions were captured in the detachment zone during early stage,while normal-pressure methane and nitrogen inclusions were captured during late stage.Fourth,the ionic constituents of inclusions recording the fluid activity during the late stage was characterized by high sodium-chloride coefficient,high desulfurization coefficient and low metamorphic coefficient,and it is indicated that the sealing capacity of the shale in the detachment zone gets worse.Fifth,the accumulation and dispersion of shale gas in the detachment zone within the study area is divided into three modes,i.e.,syncline,broad anticline and closed anticline.In conclusion,the detachment zone in the study area is permeable.Synclines and closed anticlines developed in detachment structures are unfavorable for the accumulation of shale gas,while broad anticlines are favorable.展开更多
基金supported by the National Natural ScienceFoundation of China(42102191)。
文摘Deep carbonate reservoirs affected by prominent strike-slip faults represent crucial targets in oil and gas exploration owing to their immense resource potential.However,the complex geological environments and poorly understood histories of the associated paleo-fluid activity have hindered the development of robust theories regarding pore formation and preservation mechanisms,resulting in suboptimal exploration strategies.Leveraging the extensive well deployment by the China Sinopec Group in the Shunbei area of the Tarim Basin,this study addresses these challenges by establishing a comprehensive framework for the evolution of diagenetic fluids within the Middle-Lower Ordovician carbonate formations.Using core samples,thin-section analysis,and cathodoluminescence observations,this study employs high-resolution geochemical methodologies,including isotopic analyses,rare earth element profiling,fluid inclusion studies,and uranium-lead dating,as primary tools for identifying and interpreting paleo-fluid characteristics across various rock types and calcite cement varieties within this stratigraphic interval.The findings reveal several key insights:(i)both RFC and C1 cements are derived from seawater,with C1 forming under burial conditions;(ii)C2,C3,and VC cements result from distinct tectonic events,specifically during the first and third episodes of the Middle Caledonian movement,with meteoric water infiltrating fault systems independently of orogenic belts or paleo-karst systems;and(iii)previous conclusions are challenged,as the influence of hydrothermal activity in this area is found to be minimal.Furthermore,the model presented here serves as a valuable reference for understanding fluid activity events at distal locations within orogenic belts under compressive stress,while accurately capturing fluid variations over different temporal scales within fault zones plays a decisive role.
基金supported by the National Major Science and Technology Project“Study on high-mature shale gas occurrence mechanism and enriching law in Middle Yangtze region”(No.:2016ZX05034-001-002)the Foundation Project of China Geological Survey“Investigation and evaluation of shale gas resources in Wuling and Western Hunan-Hubei area”(No.:12120114049801).
文摘The studies on the paleo-fluid in the OrdovicianeSilurian detachment zone in the MiddleeUpper Yangtze area focus on the origin of highdensity methane inclusions and the evolution process of formation pressure,but rarely deal with the significance of paleo-fluid to shale gas preservation.In this paper,the relationship between fracture formation and detachment zone was analyzed by observing the OrdovicianeSilurian outcrops in western HunaneHubei area and by investigating the geological characteristics of fracture veins in the drilling cores.Then,the significance of paleo-fluid forming environment and detachment zone to shale gas preservation was studied by using inclusion compositions of fracture veins and homogenization temperature test data.Finally,accumulationedispersion modes of shale gas in the detachment zone were established.The following results were obtained.First,the detachment zone is lithologically composed of silicite with intercalated shale at the OrdovicianeSilurian interface.In the detachment zone,rocks are broken and small crumples are developed.The conjugate-vertical joints are relatively developed in the silicite above and below the detachment zone.Second,multi-stage and multi-type inclusions,especially the aqueous inclusions,are developed in the veins of the detachment zone.Third,the infiltration depth of ancient meteoric water along the detachment zone in the study area is over 4000 m.High-density overpressure methane inclusions were captured in the detachment zone during early stage,while normal-pressure methane and nitrogen inclusions were captured during late stage.Fourth,the ionic constituents of inclusions recording the fluid activity during the late stage was characterized by high sodium-chloride coefficient,high desulfurization coefficient and low metamorphic coefficient,and it is indicated that the sealing capacity of the shale in the detachment zone gets worse.Fifth,the accumulation and dispersion of shale gas in the detachment zone within the study area is divided into three modes,i.e.,syncline,broad anticline and closed anticline.In conclusion,the detachment zone in the study area is permeable.Synclines and closed anticlines developed in detachment structures are unfavorable for the accumulation of shale gas,while broad anticlines are favorable.
