Characteristics and identification of dolomite intercalation in the Yingmai buried-hill area, northern Tarim uplift

The crack-cave type dominates dolomite reservoirs in the Yingmai buried-hill area, which include dissolved holes, karst caves and karst cracks, as well as local big unfilled caves as storage space. The bottom water massive reservoirs in dolomite buried hills are controlled by dolomite intercalation with special physical properties. Local residual oil enrichment areas are the main object in the late exploitation. Basing on analyses of cores, thin sections, physical properties and well logging data, this work made a description and identification of dolomite from Cambrian to lower Ordovician in the Penglaiba formation of the Yingmai buried-hill area. The results show that, the intercalation in this area can be classified into 3 categories, micritic dolomite intercalation, mud dolomite intercalation and powder dolomite intercalation. Vertically, dolomite intercalation mainly developed in the lower part of the shallow upward sequence in each meter scale cycles, and always spread as lens or bands of which the thickness is between 0.5 and 2.5 meters. In this area，the intercalation played the screen role to seepage and controlled the distribution of residual oil, and also affected the water breakthrough time and the rising rate in production.