Research On Diagenesis Of Chang8Oil Reservoir Group In Zhenyuan Area, Ordos Basin

Ordos Basin is the second largest petroleum-bearing basin in china, has a largeoil-bearing area and multi-energy resource minerals. The Yanchang Formation is one of themost important gas-bearing strata in Upper Triassic and abundant in natural gas resources, hasindicated a promising prospect for exploration. Zhenyuan area is located in the southwest ofthe basin. And the Chang8oil reservoir group has characteristics of ultra-low porosity andextra-low permeability and formation thickness is more stable.On the basis of earlier studies, the paper researched on the reservoir characteristics anddiagenesis types of Chang8reservoir sandstone combined with Regional geological andtectonic backgrounds of the Ordos Basin by using description and observation of drilling core,identification and analysis of thin sections, analysis of scanning electron microscope,capillary pressure data of intrusive method and X-ray diffraction. With the analysis of testdata, the paper discussed the effect of diagenesis to reservoir property, thus established amodel of diagenetic evolution and porosity evolution, and classified the diagenetic facies.The chang8member sandstone reservoir is mainly debris-feldspar and feldspar-debrissandstone. the main characterstics of the reservoir sandstone skeleton particles component iscontains a large amount of feldspar and cuttings, and deficient in quartz. The maturity ofcomposition is on low side and structural maturity is middling, particle size smaller,separating and grinding medium. Authigenic minerals in sandstone include chlorite, calcite,siliceous and kaolinite, and containing a small amount of dolomite and siderite. Reserviorspace always occur as residual original intergranular pore and all kinds of secondary porecomplex combination, give priority to with residual original intergranular pore. Micro crackdevelopment. Sandstone reservoir property mainly depends on the matrix of sandstoneporosity and the pores are positively correlated with the permeability.Diagenesis that the reservoir had experienced mainly were compaction, pressolution,cementation, metasomatism and dissliution and fracturing. Sandstone densification bycompaction, pressolution and carbonate cementation; The early chlorite rim cementation hasresulted in a part of residual primary pore sandstone reservoir were preserved. Dissolution isthe key of forming high quality reservoirs, mainly feldspar and lithic unstable particles bycorrosion, the dissolution medium including organic acid dissolution and thermal dissolution. Local microcracks caused by local tectonic movement make some pores cult-through, acted asa secondary hydrocarbon migration channel and storage. The diagenetic stage of the reservoirin the second member of chang8reservoir group in Zhenyuan area had entered into the Bstage of middle diagenesis generally.3types of diagenetic facies are developed in the studyarea, and chlorite cementation residual primary pore-calcite cementation facies is the mostprofitable diagenetic zones for developing high quality reservoir.