Diagenetic characteristics of Chang 9 reservoir in WPS area,Ordos Basin
Due to diagenetic sequence and pore evolution of Chang 9 reservoir in WPS block is not yet clear,this study characterizes the reservoir,diagenesis and porosity evolution process of Chang 9 through experimental data from thin section analysis,casting sheets,scanning electron microscopy,whole rock X-ray diffraction analysis and high-pressure mer-cury intrusion,revealing the influence and control of diagenesis on the evolution of reservoir porosity.The results shows,(1)The Chang 9 reservoir in the study area is mainly developed with medium-fine grained arspathic sandstone,which pre-dominantly features intergranular and secondary dissolution pores,with an average porosity of 12.3％and an average per-meability of 4.57 mD.It exhibits low-porosity and low to ultra-low permeability characteristics.(2)The member mainly experienced 4 types of diagenesis including compaction,cementation,corrosion and metasomatism,Corrosion is a con-structive diagenetic process,which plays an important part in forming high-quality reservoirs.Compaction and cementa-tion are destructive diagenetic processes,which greatly reduce the reservoir physical properties.(3)Based on the porosi-ty and diagenetic evolution parameters at each stage of diagenetic quantitative restoration,the average value of original porosity is 39.97％,the average value of compaction porosity reduction is 56.025％,the average value of cementation po-rosity reduction is 24.82％,and the average value of solution porosity increase is 10.96％.(4)According to studies on dia-genetic sequence and burial history,the porosity evolution experienced three stages including early diagenetic stage(compaction+early cementation)-porosity reduction,middle diagenetic stage A,(dissolution)-porosity increase,and middle diagenetic stage A2(late cementation+oil and gas charging)-porosity reduction.The porosity drops to 12.03％before halting.The pore evolution process is reasonably restored by methods in study.In this paper,with qualitative and quantitative analysis to study diagenesis and pore evolution is practical significance for the formation mechanism、the comprehensive evaluation and prediction of favorable sweet spots and the subsequent exploration and development.in the same reservoir.
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