A Novel Study on Classification Method of Complex Carbonate Reservoir Type: A Case on XX Oilfield in the Caspian Basin

In this paper, a novel method is carried out for reservoir classification research on carbonate reservoir of XX oilfield in the Caspian Basin. It is applied to determine the types of carbonate reservoir based on core, mercury injection analysis, conventional logging data and oil testing information. In the process of oil and gas exploration and development of carbonate reservoir in XX oilfield, reservoir type is one of the basic research, which plays a guiding role in determining reserves and the exploitation method adopted by the oilfield. In 5 wells of XX oilfield, core analysis, oil testing, conventional logging, mud logging and other related data were obtained. Based on the analysis of these data, the petrological characteristics and pore structure of the reservoir were systematically studied; the reservoir can be divided into different reservoir types: fracture-type, pore-type, pore-hole/vuggy-type, composite-type (pore, fracture) and non-reservoir. In this study, based on the analysis of the median radius of pore throat (RC50), the reservoir permeability analysis parameter (Para_K) was introduced in, the reservoir structural parameter (IPS_Str) was calculated and normalized. The intersection diagram of porosity and reservoir structural parameters of various reservoir types was obtained, and the reservoir identification chart of XX oilfield can be obtained. For most reservoirs to be classified without coring, the artificial intelligence fitting relationship between conventional logging response and the RC50 was established to calculate the RC50 of non-coring sections and wells. Combined with the reservoir permeability analysis parameters, calculating and normalizing the reservoir structure parameters, the intersection diagram of porosity and normalized IPS_Str of non-coring well sections and wells is prepared, and the reservoir types can be classified and gained. This study aims at carbonate reservoirs, overcomes the technical difficulties of using conventional logging to identify reservoir types for a long time, provides a new classification method for complex carbonate reservoirs, solves the technical problems of low classification accuracy and difficult classification of complex carbonate reservoirs in existing technologies, and has a good promotion and application prospect.