Comprehensive Interpretation Of 3D Seismic Data And Optimization Of Favorable Areas In Shancheng Area Of Ordos Basin

Shancheng area in the middle and southern part of Tianhuan Depression is a multi-reservoir complex development area.A large number of industrial wells and low-amplitude structural reservoirs have been found in Yanchang Formation,of which the reservoirs of Chang6 and Chang8 are dense and highly inhomogeneous.As the main reservoir section of Triassic Yanchang Formation,the former 2D seismic exploration were unsatisfactory,and the reservoir development characteristics and main control factors need to be further clarified.These low-amplitude structural reservoirs are characterized by small size and fertility,mainly concentrated on the slope zone on both wings of Tianhuan syncline and local uplift in the middle of syncline,with great exploration and development potential.According to the characteristics of reservoir enrichment in Shancheng area during past two-dimensional exploration by Changqing Branch,the difficulties faced by Yanchang Formation reservoir in Shancheng area are thin reservoir and poor physical property,difficult reservoir prediction,structure,source rock and fault（fractures）all affect oil and gas enrichment,and difficult to predict dessert.In response to the above problems,guided by petroleum geology,sedimentology,sequence stratigraphy,seismic stratigraphy,etc.,referring to the general situation of Yanchang Formation in surrounding area of Shancheng and understanding of previous 2D exploration,this study utilizes high-quality three-dimensional seismic data and on-well data in Shancheng area to re-control strata,structural interpretation and reservoir prediction of target strata of Yanchang Formation,and comprehensively analyze the main control factors from the perspective of petroleum geology.On this basis,the favorable zones are optimized and classified,and the accuracy of this study is verified by combining late exploration results and horizontal well deployment.The research shows that:（1）Both curvature and coherence attributes can describe fracture,but curvature attributes are highly sensitive to fracture,and are suitable for characterizing some small-scale fractures.The higher degree of fracture can be better described by coherence attributes.（2）The fault system in Shancheng area is well developed with obvious fault characteristics in each stage.Three-phase faults are mainly developed in Mesozoic target strata in Shancheng 3D,including Yanshanian,Indosinian and Himalayan faults.Vertical characteristics of sections show that the third stage faults all started in Caledonian period with different defining periods:the heavily developed NE faults were defining in Himalayan period,and the seismic sections showed negative flower-like characteristics with fault spacing of 5m-35m and extension length of 0.5km-15km.The Yanshanian Yanlian type near NS trending faults developed in the southeast are characterized by inherited development with a fault distance gradually increasing from depth to shallowness and a length of 5m-20m.It has certain control effect on early reservoir.Faults in Indosinian period seldom develop in the area,mainly due to the weakening of tectonic action in this period caused by the stress action of SN section,and its control effect on reservoir is not obvious for the time being.（3）Structures are relatively flat,nose-shaped uplifts and low-amplitude structures are locally developed,which generally represent a structural pattern of low west to high east and structural inheritance of each layer is well developed.Affected by multi-stage tectonic movement and controlled and separated by Himalayan faults,a series of anticline,fault block and fault back structures have been formed.These local structures play an important role in the longitudinal and transverse migration and accumulation of oil and gas.（4）The main factors controlling reservoir in Chang8 section are relatively high positions of present structure and paleostructure,the thickness of source rock is the second important factor,and the reservoir thickness has no obvious influence on reservoir;（5）The thickness of source rock and the sand body in front of the precursor are the main factors for reservoir control of Chang6 section.The structure has little relationship with oil and gas,and the lithologic reservoir characteristics of Chang 6 section are obvious.（6）Chang8 is a structural-lithologic reservoir with characteristics of upper generation and lower storage,which can be divided into two favorable zones.Among them,there are 4 favorable zones of Class I in Chang8₁with an area of 86.12km²;There are 13 favorable zones in Class II with an area of 32.47 km².24Category I favorable areas in Chang8₂,with an area of 25.19 km²;There are 11 favorable zones in Class II with an area of 34.89km².（7）Chang6 section is located above the hydrocarbon-generating layer Chang7 and has the characteristics of lower generation and upper storage.According to the lithological reservoir characteristics,it can be divided into two favorable zones,of which 6 are classified as Category I favorable zones with an area of36.1km².There are 5 favorable zones in Class II with an area of 15.6km².In Chang6₂,there are 3 favorable zones of Class I with an area of 36.5km².There are 6 favorable zones in class II with an area of 17.07 km².The enrichment causes and regularities of main reservoirs of Mesozoic Triassic Yanchang Formation in Shancheng area of Ordos Basin are analyzed in order to provide certain reference value for exploration of heterogeneous reservoirs and reservoir development in surrounding areas.