Research on Diageneses of Cambrian Shoal Facies Carbonate Rocks in the Xiadong Area, Hubei Province

AbstractWith continuous outcrops, developed shoal facies rocks, complete types of diagenesis and changeable diagenetic environments, Cambrian strata are well developed in the Xiadong area, Yichang, Hubei Province. Under the combined influence of numerous diageneses, secondary pores can be formed, which result in better reservoir properties of the rock strata.The Cambrian rocks in this area consist of mainly carbonate rocks and secondarily detrital rocks. The carbonate rocks are dominated by grainstones including wormkalk, calcirudite‐calcarenite, oolitic limestone and oncolitic limestone. Graded bedding and cross bedding are well developed in the strata, which indicates that the formation environment is of a high‐energy shoal facies.In this area, there has developed a sequence of stable Cambrian platform carbonate deposition. The evolution trend is as follows: open sea shelf faciesŕintertidal low‐energy restricted sea faciesŕintertidal high‐energy shoal faciesŕcoastal shoal faciesŕevaporite tidal‐flat facies.The diageneses that the strata have experienced mainly include dolomitization, dedolomitization and dissolution, which are constructive diageneses for the formation of secondary pores, such as intercrystal pores, intercrystal solution pores, gypsum mold pores and caverns of dolomite.The diagenetic facies intervals can be divided into the unitary and the compound ones, totalling 22 in the area.In the early atmospheric fresh‐water diagenetic environment and the late epidiagenetic environment, Cambrian rocks, especially dolomite of the Middle and Upper Cambrian, experienced extensive and profound fresh water corrosion, forming pore intervals with a porosity ranging from 5% to 15%.