Lithogenic and accumulation characteristics as well as quality affecting factors of Middle-Upper Cambrian strata and Sinian Denying Formation dolomite reservoirs on the western side of the Xuefeng Mountain

Middle-Upper Cambrian strata and Sinian Denying Formation dolostones on the western side of the Xuefeng Mountain constitute important potential reservoirs. Reservoir characteristics are described based on petrologic, mineralogical, and petrophysical analysis. The lithfacies include mainly crystalline dolostones, remnant grained dolostones, calcareous dolostones, and algal dolostones. Depositional facies and various types of diagenetic alterations have caused considerable deterioration and heterogeneity in the target reservoirs. The carbonates have been subjected to extensive diagenetic actions such as recrystallization, dolomitization, dissolution, calcite cementation, and fracturing. Fine crystalline dolomites have higher porosity than microdolomites and coarse crystalline dolomites. There is a clear relationship between porosity and degree of dolomitization in the target strata, suggesting that dolomitization enhances porosity. Porosity in the target layers includes intercrystalline (remnant and solution-enlarged), secondary, vuggy, and fracture types. In general, dolomitization, recrystallization, fracturing, regional open environment, and late stylolites caused by pressure dissolution are beneficial to the development of high-quality reservoirs.