Characterization And Classification Evaluation Of Pore Structure Of Chang 7 Reservoir In Block 233,West Qingcheng Oilfield

The Ordos Basin is rich in tight oil and gas reserves,but there are problems such as poor physical properties,complex pore structures,and high difficulty in exploration and development,therefore,accurately and comprehensively characterize the pore structure of tight reservoirs in this area,and identify its influencing factors,it is of great significance for clarifying the microscopic difference mechanism of tight oil reservoir quality and later development.The research object of this paper is the tight sandstone reservoir of the Chang 7 in the West 233 well area in the southwest of the Ordos Basin,characterization and classification evaluation of pore structure are carried out through various analysis and testing methods,the petrological and diagenetic characteristics of the study area were clarified,and the development patterns of different pore structure types were clarified,a reservoir quality evaluation standard based on pore structure has been established to predict high-quality reservoirs in the target block.The sandstone in the study area has a low compositional maturity and fine particle size,mainly composed of fine sandstone and siltstone,with good sorting and moderate psephicity.The pores are mainly intergranular pores and dissolution pores;Submicro to nano sized throat development,the radius ratio of pore to throat is large,strong heterogeneity of pore structure The saturation of movable fluid in the reservoir is relatively low,and the movable fluid is mainly controlled by micron sized pores and throats,the bound fluid is mainly concentrated in submicron to nanoscale pore throats;Combined high-pressure mercury injection and constant velocity mercury injection,the full aperture distribution and fractal study of the pore throat size of the reservoir in the study area have been achieved,the results show that the full pore size distribution can characterize pore size characteristics ranging from a few nanometers to several hundred micrometers.Pore structure is influenced by sedimentary microfacies,rock composition,fabric,and diagenesis.The pore throat structures of different sedimentary microfacies differ significantly,the pore throat size,distribution,and connectivity of the channel microfacies are significantly better than those of the main body and lateral edge of the leaflet;The higher the quartz content of the rock,the lower the carbonate cement content,and the lower the clay mineral content,the larger the pore throat,the more uniform the distribution,and the better the connectivity;High roundness and good sorting are also conducive to the development of high-quality pore structures;Cementation and compaction play a destructive role in the development of pore structure of the reservoir,while dissolution plays a certain role in improving the reservoir.Using machine learning,pore structure classification and evaluation are conducted,and pore structures are divided into four categories based on differences in mercury intrusion and physical properties,established logging interpretation templates for different types of pore structures,and verified that the accuracy of the discovery results reached over 90%.A reservoir classification evaluation standard based on differences in pore structure characteristics has been established to predict high-quality reservoirs in the target block,the results show that high-quality reservoirs are mainly distributed in the thicker sand bodies in the middle of the channel microfacies close to the provenance,a few high-quality reservoirs are distributed in the main microfacies of the lobe with good physical characteristics,mainly in a lenticular distribution.