Study On Antithetic Fault-controlled Reservoir Model In The Tanan Sag Of The Haita Basin

This paper aimed at the scientific problems concerning sealing characteristics of antithetic faults and their controlling effect on hydrocarbon accumulation in the Tanan Sag of the Haita Basin.Based on the theories of structural geology,sedimentary petrology and hydrocarbon accumulation,intergrating the techniques of well seismic combination,fault sealing ability evaluation and favorable zone evaluation,the the characteristics and their controlling effect on hydrocarbon accumulation of antithetic faults were carried out in the Tanan Sag,and the reservoir forming model were established and the favorable zones in the fault-controlled traps were pedicted.The faults in the Tanan Sag have different distribution characteristics interms of scale.High level faults are different from low level faults,the fault direction within the second member of Nan Formation is mainly NNE,and the fault direction within the first member of Nan Section and Tongbomiao Formation are basically NE.The fault sealing capacity are featured with horizontal and vertical differentiation.The antithetic fault sealing capacity of the middle subsag and the west wing of the faults in middle buried hill zone are the best,followed by the antithetic faults in the eastern subconcave.The antithetic faults are better than that of consequent faults,and the upper faults are better than the lower faults when it comes to the fault sealing capacity.During the sedimentary period of Tongbomiao Formation,the antithetic faults activity was strong.Hence the faults were deemed open with good conductivity.The antithetic faults were believed sealed with poor conductivity in the sedimentary period of南二段.During the sedimentary period of the Damoguaihe Formation,NNW trending faults are always highly active,providing effective mirgration channel during hydrocarbon generation and expulsion periods.Controlled by antithetic fault shading,oil and gas are clustered by faults in shape of straps horizontally and vertically.The main controlling factor of reservoir formation in the Tanan Sag is antithetic fault,and the reservoir type is dominated by antithetic fault reservoir.During the sedimentary period of the Tongbomiao Formation to the Nantun Formation,oil and gas mainly transported vertically along antithetic fault,together with lateral mirgration within unconformity and sand body.During the sedimentary period of the Damoguaihe Formation,lateral transport within unconformity and sand body is dominant,along with vertical transport within antithetic fault.During the sedimentary period of the Yimin Formation,vertical transport of antithetic fault is dominant.On the basis of the accumulation process mentioned above,it is clear that the hydrocarbon accumulation was significantlly controlled by the antithetic fault.Three hydrocarbon accumulation models were established,namely antithetic fault vertical transport-antithetic fault lateral occlusion reservoir forming model,antithetic fault lateral occlusion/lithology reservoir forming model and unconformity lateral transport-antithetic fault reservoir forming model.Based on favorable geological conditions of structure,deposition,reservoir,antithetic fault sealing characteristics and reservoir formation,the north trough of the middle subsag was selected as the favorable area.In addition,due to the abundacne of sand bodies within N₂II oil group and N₂I oil group in T19-67 and T19-17 blocks with good connectivity,high single layer thickness and sufficient supply of oil source,a large number of reservoirs are developed under the control of antithetic faults.Therefore,it can be a favorable area for further oil and gas exploration.