Research On Reservoir Geological Characteristics Of Chang1 Oil-bearing In Xirengou Of Dingbian Oilfield

The Xirengou oil region of Dingbian oilfield is located at the western edge of the North Shaanxi slope in the Ordos Basin.The main layer series of development in the study area are the Chang 1 oil-bearing formation,with a focus on Chang 12 layer.The research area has entered the late term of development.There is a rapid decline in production,rapid increase in water content,poor or ineffective water injection.The poor development effect and poor overall development is due in large part to the fact that the understanding of the geological characteristics of the reservoir is not sufficiently detailed,So it could not guide the water injection development adjustment and deployment plan effectively.The purpose of this paper is to finely anatomize the geological characteristics of reservoirs.Based on previous research,a large number of geological data,well logs,logging data,production data and test analysis data were used to classify strata of the study area,study the characteristics of sedimentary microfacies in reservoirs of planar and vertical distribution,the structural characteristics and heterogeneity of sand bodies in reservoirs,and the four properties' relations of oil reserviors.Then,Analyzing and determining the reservoir characteristics of the Chang 1 oil-bearing formation and the main controlling factors of oil and gas enrichment,which will provide direction and basis for the next step of oilfield development adjustment program deployment.The structural characteristics of the study area show that there are 3 structural noses on the background of high west and low east.During the Chang 12 period,study area develop delta plains subfacies.The main types of sedimentary microfacies were the deltaic plain distributary channel and inter-distributary bay.The distributary channel was the skeleton sandbody in the study area,and 5 distributary channels developed from the northeast to southwest.Two distributary rivers develop from the northwest to the southeast,separated by inter-distributary bay,and several distributary channel sand bodies converge at the middle of the study area and become favorable reservoir.The type of sandstone in the study area Chang 1 reservoir is feldspar or debris-feldspar sandstone.Kaolinite,chlorite film,hydromica,calcite,and iron dolomite are the main types of interstitial material,and the pore types are mainly residual intergranular pore and feldspar pores.Porosity range is mainly distributed between 10% and 15%,the average value is 13.2%,permeability range is mainly distributed between 2m D ~ 50 m D,the average value is 22.5m D;pore throat type is coarse-medium-thin throat,Chang 1 sandstone reservoirs have lower displacement pressure,ranging from 0.06 MPa to 1.166 MPa,with an average value of 0.138 MPa;median pressure distributions range from 1.3725 MPa to 2.478 MPa,with an average value of 1.705 MPa;it shows that the pore connectivity of the reservoir is good.The reservoir of Chang 1 in the study area belongs to low porosity and low permeability reservoir.The heterogeneity of the Chang 1 reservoir is strong,and the heterogeneity of permeability mainly develops positive rhythm and compound rhythm;the development and distribution of the interlayer also have a great influence on intra-layer heterogeneity.Sand body configuration are mainly superimposed waterways and isolated waterways in the vertical direction,and the sand bodies are better connected laterally.Reservoir heterogeneity is mainly affected by the sedimentary environment,and it is controlled by sedimentary microfacies and main sand body belts.Based on the " four properties' relations " study in the study area,Lower limit of lithology of Chang 1 reservoir is fine sandstone,the lower limit of oily production is oil spots,the lower limit of porosity of effective reservoirs is ?10.3%,and the lower limit of permeability is ?3.5m D,the lower limit of electrical conductivity of the target layer is RILD ? 6?·m,AC ? 240 ?s/m,and So ? 25%.The Chang1~2-layer reservoir of the study area is more concentrated in the overlapping contiguous bodies of distributary channel sand bodies in different directions.The overall structure extends from the northeast to the middle and then to the southeast in strips;the type of reservoir is the structure-lithologic reservoirs.Due to differential compaction,cause nose-shaped uplift at the superposed and contiguous locations of the sand bodies.The center of the sand body is often located at the highest part of the nose-shaped structures.Nose-shaped structures,distributary channel skeleton sand bodies and shielding of inter-distributary mudstone have a allocation relation that forms good trap.