Distribution Of Lower Combination Oil And Gas In Xiasiwan Area,ordos Basin

In recent years,great breakthroughs have been made in the exploration of upper combination reservoir group in Xiasiwan area of Ordos Basin,showing good exploration prospects.However,due to the increasing demand for actual production and the decline of productivity of old formation,it is necessary to look for resources in the lower part of Yanchang Formation.However,in the past,less attention has been paid to the lower combination reservoirs,and the distribution of exploration wells and evaluation wells is extremely uneven.In order to effectively explore oil and gas fields and reasonably develop oil and gas fields,it is necessary to understand the underground structural characteristics of oil and gas fields in detail and correctly.Based on logging and logging data,field outcrop and previous studies,the lower combination chang7-chang10 are divided into eight sub-layers:chang7₁,chang7₂,chang7₃,chang8₁,chang8₂,chang9₁,chang9₂,chang10₁(In this paper,most wells are drilled to the top of chang10,so they are only divided into chang10_1-1-1 and chang10_1-2)On the basis of stratigraphic correlation and division,combined with previous analysis data,the sedimentary facies types of each layer are defined through the single well sedimentary facies and the plane distribution of sedimentary facies.It is considered that Chang7 mainly develops semi-deep lake——deep Lake subfacies,followed by delta front deposits;Chang8 and Chang9 mainly develops delta front subfacies,Chang9 also develops semi-deep lake——deep Lake subfacies;Chang10 develops delta plain subfacies deposits.Through reading the literature,we can grasp the petrological characteristics,diagenesis and physical properties of the lower combination reservoirs in the study area:sandstones of each layer in the lower combination are mainly feldspar sandstone and lithic feldspar sandstone;the pore types of the rocks are mainly intergranular pore and intragranular dissolution pore,and the main pore throat combination is micro-pore and micro-throat.It has undergone compaction,cementation,dissolution and other digenesis.The physical properties of the lower combination reservoirs are poor.The porosity mainly ranges from 5%to 10%,and the permeability is between 0.1 and 0.2 mD.It belongs to ultra-low porosity and ultra-low permeability reservoirs.After understanding the reservoir characteristics,sedimentary microfacies and structural characteristics of the study area,combined with oil testing data,the top structure contour map,sand body thickness contour map and sedimentary microfacies plane map of each sub-layer in the study area.Combined with previous research results,the oil and gas distribution law of the study area is summarized,which provides a strong basis for future exploration and development.