Sedimentary And Reservoir Characteristics Of Xishanyao Formation In Southern Limb Of Chemo Palaeohigh

The Chemo palaeohigh is an ancient anticline-type uplift formed during the Yanshanian in the abdomen of the Junggar Basin.This area has excellent reservoir-forming conditions and abundant oil source conditions.However,due to factors such as low level of exploration research and large depth of target layer,further research is needed on the study area.In this paper,the sedimentary characteristics,diagenesis characteristics,reservoir characteristics and control factors of the Xishanyao Formation in the study area are studied by combining core data,grain size data and analytical data.The Xishanyao Formation in the whole study area developed braided river delta deposits.In the early stage of the sedimentation of the first sand group,the braided river delta front subfacies were developed,and the accumulated floodwaters depression formed by the late floods were gradually covered by vegetation,and developed into a swampy environment of the braided river delta plain,forming a large coal seam.During the whole sedimentary period of the second sand group Formation,the supply of material sources gradually decreased,and the sedimentary center gradually migrated to the northeast direction.The study area develops the subaqueous distributary channel and the diversion bay of the braided river delta front subfacies,showing a regressive type.Through the analysis of diagenesis,it is found that the burial depth of the Xishanyao Formation in the study area is greater than 5300m,and the diagenetic stage is mainly in the stage A of Medium diagenetic stage,and some may reach the B stage of the Medium diagenetic stage.The diagenesis that has a major impact on the reservoir is compaction and dissolution.The dissolution of the fracture zone is particularly strong,because the fracture communicates with the acidic fluid to dissolve the feldspar and carbonate cement in the reservoir,improving the storage.The study area can be divided into 10 diagenetic facies.Strong compaction medium cementation strong dissolution phase is the most favorable diagenetic facies in the study area,mainly developed in J₂x₂¹and J₂x₂²of Yong 1 well and Yong 2 well.The development of the fracture controls the quality of the entire Xishanyao reservoir.The porosity of the fracture development site is obviously increased,and the oil content is good.It constitutes a favorable reservoir and shows a phenomenon of non-oil or dry.The abnormal high pressure controls the formation of cracks in the study area as an external factor,and mainly forms cracks in the pressure storage tank mode.In the overpressure environment,the vulnerable point of the rock deformation(stress weak surface)is the concentrated discharge point of the overpressure fluid,and the formation pressure and fracture pressure of these parts,which called opening pressure is minimal.This is more conducive to cracking and opening of the formation.The formation condition of the weak surface of the stress acts as an internal factor affecting the fracture of the rock.According to research findings,the main controlling factors for the development of stress weak surface in Yongjin area are the difference of mud content and the difference of lithofacies combination.Finally,combined with the distribution law of sedimentary microfacies in the plane and longitudinal direction,combined with the research results of reservoir control factors,the favorable sand bodies are predicted.In the longitudinal direction,the No.3 single sand body of J₂x₂¹is adjacent to the packing layer,which is an advantageous target layer;the favorable sand body on the plane is distributed in the connection range of Yong 1 well and Yong 3 well or in the north east direction of Yong 3 well.