Study On Well-Logging Diagenetic Facies And Key Parameters In Low Permeability Reservoir

Yanwu area is located in the southwestern margin of Ordos Basin.The study of main oil-producing layers shows that the sandstone reservoir of Yanchang Formation of Upper Triassic is a low permeability reservoir,and the diagenetic facies is one of the main factors controlling oil and gas accumulation in this area.In order to solve the problem of"low contrast,low adaptability"and"non-linearity"faced by logging technology in low permeability reservoirs,identify diagenetic facies accurately for large-scale unconcored formation,and then to evaluate accurately the reservoir key parameters,this paper,guided by sedimentology,reservoir sedimentology,logging geology and petroleum geology,makes a comprehensive study of the petrological characteristics,microscopic pore structure,diagenesis facies and logging diagenesis facies of reservoirs in the 8th member of Triassic Yanchang formation in the southwestern margin of Ordos basin by means of core observation,thin section and grouting thin section identification,X-ray diffraction analysis,mercury intrusion test and scanning electron microscopy.The reservoir of the 8th member of Yanchang formation in Yanwu area is characterized by gentle landform and stable structure.It is a set of meandering river delta plain deposits with no large cross section between delta plain,front edge and front delta subfacies,and mainly develops sedimentary microfacies such as underwater distributary channel,channel sand dam,underwater distributary channel and underwater distributary channel side edge.The material source direction is southwest,and the sand body is widely distributed,thick and extended.The composition maturity of the sandstone of the 8th member of Yanchang formation in the study area is relatively low,mainly fine-grained feldspar clastic sandstone,with a small amount of lithic feldspar sandstone,and minor lithic lithic sandstone,minor lithic feldspar sandstone and lithic sandstone are rare.The interstitial materials are mainly cementation or replacement of argillaceous and carbonate materials,with occasional turbidite and pyrite.The interstitial material is mainly filled in the primary intergranular pores between particles,and the reservoir physical properties are usually poor in the sandstone with high content.The sandstone reservoir of the target layer in the study area has undergone diagenesis such as compaction,cementation and dissolution in the process of diagenetic evolution,and the sandstone shows the characteristics of residual primary intergranular pores and a large number of secondary pores.The study shows that a large number of secondary pores generated by dissolution are the main control factor for reservoir physical property modification.Physical property analysis shows that the porosity in the target layer is mainly 3.21%-12.1%and the permeability is 0.1-4×10^-3um².Reservoir heterogeneity is strong,it is a typical low porosity and permeability reservoir.According to the contact characteristics of particles in rocks;Pore combination type,the composition,morphology,occurrence,generation sequence and combination characteristics of authigenic minerals determine that the diagenetic stage of sandstone in the target interval of the study area is intermediate diagenetic stage A.Among them,compaction,pressure dissolution,siliceous cementation,clastic particle fracture and feldspar dissolution exist in all diagenesis stages,with overlapping diagenesis in different stages.Diagenetic facies are divided according to sedimentary diagenesis and the types and occurrence of main cements controlling reservoir physical properties.The constructive diagenetic facies are chlorite lining weak dissolution diagenetic facies and unstable component dissolution diagenetic facies.Destructive diagenetic facies are compact diagenetic facies,kaolinite filling diagenetic facies and carbonate cementation diagenetic facies.According to the analysis of diagenetic facies and logging response characteristics of the reservoir in the 8th member of Yanchang Formation in Yanwu area,neutron logging,density logging,natural gamma logging,resistivity logging and neutron-density apparent limestone porosity difference logging curves are proposed as logging diagenetic facies evaluation parameters,and the logging diagenetic facies are identified by gray cluster analysis.In order to ensure the accuracy of logging diagenesis,hole diameter correction and depth homing were carried out for each sample point.Through a large number of cast thin sections,ordinary thin sections,scanning electron microscopy and high-pressure mercury injection,the pore characteristics,pore combination characteristics and pore throat structure characteristics of reservoir rocks in Chang 8 are analyzed,pore structures are classified,and pore structure parameters are evaluated using conventional logging data.The characteristics of sand layer thickness,porosity,permeability,maximum mercury saturation,pore radius,capillary curvature,oil saturation and displacement pressure are selected,and fuzzy comprehensive evaluation method is used to comprehensively evaluate the reservoirs in the 8th member of the study area and predict favorable areas.As to the problems existing in the logging evaluation of low permeability sandstone reservoirs,relatively systematic analysis of ideas and solutions are put forward to provide technical support for logging evaluation of the complicated low permeability sandstone reservoirs.