| Block Qie 12 of Kunbei oilfield in Qaidam basin is a typical ultra-low permeability glutenite reservoir.The main oil-bearing section is the Low-Ganchaigou formation?E31?.The glutenite reservoir in block Qie 12 is composed of multi-stage fan bodies superimposed.The longitudinal sedimentary thickness changes greatly,the lithofacies changes rapidly,the rock structure maturity and the component maturity are very low,and the reservoir heterogeneity is very strong,which brings difficulties to reservoir prediction,oil-gas-water layer identification and logging interpretation.In the exploration and development in recent years,problems such as water injection burst and invalid water injection circulation are caused.Based on the theories of sedimentology and reservoir geology,this paper carries out a comprehensive study on the reservoir characteristics of ultra-low permeability glutenite reservoir in block Qie12.Based on the analysis of sedimentary facies markers and logging curves,it is concluded that alluvial fan deposits are developed in the study area,which can be divided into the sedimentary subfacies of fan root,fan and fan edge.And it can be further subdivided into 8 sedimentary microfacies,such as braided channel,flood sand body microfacies,etc.The distribution of facies in plane was determined by the single well facies data and the provenance direction of the research area.Through core observation,X-ray diffraction and statistical analysis to research reservoir characteristics from the petrology,diagenesis,pore characteristics,physical property features.The target stratum has granularity coarser,which is mainly for the pebbly sandstone.The pore types is mainly primary intergranular pore.The porosity is8-12%,the average was 9.17%.The average permeability is 4.36×10-3?m2,which concentrated on 0.1-5×10-3?m2,so it's low porosity and permeability reservoir.The porosity and permeability of the braided channel microfacies were the best,followed by the sedimentary microfacies of the diffuse sand body,then the pelagic sand and gravel body,and the diffuse fine grains were the worst.Reservoir heterogeneity is studied in this paper.It is considered that the physical intercalation is the main intraformational bed in block Qie 12,which is mainly manifested as composite positive rhythm type.All the parameters reflect that the heterogeneity is very strong,and the plane heterogeneity is restricted by the physical property and configuration of the reservoir.The differences among the small layers are great.The reservoir characteristics and heterogeneity were quantitatively characterized by the comprehensive evaluation index method.According to the planar distribution map of reservoir quality index,it can be concluded that the types of reservoirs and sand bodies in each small layer vary greatly.The physical properties and quality coefficients of the reservoirs in the high part of the block are high.The physical properties of the reservoirs in the roots and edges of the alluvial fan are poor,and the permeability levels of the small layers in plane are between hundreds and thousands.On the basis of reservoir analysis,the criteria of reservoir classification and evaluation are established to divide the reservoir into categories ?,?,? and ?.Based on the reservoir classification evaluation single well oil and sedimentary characteristics,oil reservoir classification is completed and the plane distribution characteristics of oil reservoir classification is determine,which can be concluded that main layer developments ?,?,reservoir.The minor layer is mainly ? type reservoir,which has small sand body and poorly continuity. |
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