Study On Fault-Caprock Coupling Reservoir Controlling Mechanism In Longfengshan-dongling Area In Changling Faulted Basin

Applying the theories and methods comprehensively of the petroleum geology,structural geology,geophysics,rock mechanics,mineral petrology and petroleum geochemistry and so on,taking the research of spatial effectiveness of fault-caprock as the core,mechanism of fault-caprock coupling for controlling reservoir in Changling faulted basin was deeply discussed,the fault-caprock coupling controlling reservoir model was studied.Combined with regional geological backgroud,the activity and sealing capacity of faults in study area were evaluated quantitatively,the relationship between the spatial effectiveness of faults and hydrocarbon migration and accumulation was clarified.The faults in Longfengshan area can transport hydrocarbon vertically in the early-middle stage of the first accumulaiton period?106.3¹03.0Ma ago?while it behaved good sealing property in the late first accumulaiton period?103.0¹01.5Ma ago?and the second accumulaiton period?94.5⁸1.5Ma ago?,leading to hydrocarbon migrating from south to north along connected sand body in corridor space formed by sealing faults.The faults in Dongling area can transport hydrocarbon vertically in the first and early stage of the second accumulaiton period?106.3¹01.5Ma and94.5⁹0.0Ma ago?,hydrocarbon transported along laddder-like multiple transportion pathways formed by faults and sand body,the faults had poor sealing capacity in middle and later periods of the second accumulaiton stage?90.0⁸1.5Ma ago?,hydrocarbon migrated laterally along faults.In microcosmic and macrocosmic view,static characteris of caprocks were evaluated.Macroscopically,mudstone caprocks of K₁yc³ sand group in Longfengshan area were the main caprocks with large thickness and good continuity.There were several sets of caprocks from K₁yc to K₁q in Dongling area,the caprocks of K₁yc³ and K₁q² were the main caprocks with large thickness and distribution area.Microscopically,compared with Dongling area,the main caprocks of Longfengshan area had lower porosity and permeability,higher displacement pressure,higher clay mineral content and better sealing capacity.Mechanical properties of caprocks were evaluated by triaxial compression tests and triaxial unloading pressures tests,combined with burial history of caprocks,the dynamic evolution pattern of caprocks could be clearly defined.Mudstone caprocks of K₁yc³ sand group in Longfengshan area were in the stage of brittle deformation during the first accumulaiton periodand in the stage of ductile-brittle deformation during the second accumulaiton period,caprocks had high sealing capacity at present with semi-ductile and ductile conditions.Caprocks of K₁q² and K₁yc³ in Dongling area were in the phase of brittle deformation during accumulaiton stage with poor sealing capacity.Spatial effectiveness of fault-caprock configuration was evaluated by faulted-contact thickness method and SGR lower limit method ant its dynamic evolution pattern.Due to high fault-contact thickness and SGR which was higher than SGR lower limit,sand group of K₁yc³ in Longfengshan area can provide good vertical barrier condition for hydrocarbon and hydrocarbon mainly accumulated in K₁yc³ group.In Dongling area,primary hydrocarbon reservoirs were formed during first accumulaiton period with good fault-caprock configuration of K₁yc³,so that hydrocarbon accumulated dispersedly,then the continuity of the caprocks of K₁yc³ was destroyed by the faults in the second stage of hydrocarbon accumulaiton,hydrocarbon effused and redistributed beneath K₁q² caprocks with good fault-caprock configuration,and the reservoirs were highly overlapped and connected.Based on the identification of fault zones internal structure,combine with caprock mechanical properties,ductile-brittle properties of caprocks were considered to control the orderly changing of fault zones structure type and the continuity of shale smearing,then control the relationship between faults and hydrocarbon migration and accumulation at motionless stage.The developing model of faults zones changed from incomplete type?₁ to complete type to incomplete type?and to incomplete type?₂ with deepening of strata and mechanical properties changing from ductile to brittle.Therefore,brittle formations in Dongling area developed incomplete type?₁-complete type faults zones with poor sealing capacity,and its continuity of clay smear is relative poor,so that hydrocarbon can migrate laterally.Ductile-brittle formations in Longfengshan area developed complete-incomplete type?-incomplete type?₂ faults zones with good continuity of clay smear and good sealing capacity which can be the laterally barrier of hydrocarbon accumulation.In light of the comprehensive analysis of fault-caprocks'spatial effectiveness and configuration and the quantitatively evaluation of fault-caprock coupling for controlling reservoir,compound reservoir controlling model of“follow-source conduction,reverse sealing,ductile-brittle sealing caprocks”in Longfengshan area and“back-source conduction,laddder-like migration,brittle sealing caprocks”in Dongling area were established.