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Carbonate reservoirs are characterized by strong heterogeneity and complex lithologies as they have undergone complex comprehensive reformation in aspects of sedimentation, diagenesis, and tectogenesis. The fine lithologic discrimination of these reservoirs is difficult, resulting in difficulties in reservoir prediction and efficient reservoir development. In this paper, the carbonate reservoirs of North Truwa Oilfield in Kazakhstan are taken as an example to simply classify the oilfield lithology into the lithologies of grainstone, packstone, wackestone, crystalline dolomite, mudstone, and gypsum, and the log response characteristics of different lithologies are summarized, based on extensive core observation and thin section analysis and by the naming and classification of Dunham, Folk, et al. With the machine learning method, the thin section identification results of 2 coring wells are used as training samples, and the lithologic discrimination training model is established by using the multi-resolution graphbased clustering (MRGC) method; on theses bases, the lithology is predicated through the k-nearest neighbors (KNN) algorithm, and verified with the thin section lithologic information of other coring wells. As suggested by application results, this method can provide an overall coincidence rate of up to 87.8%, and thus can be used for high-precision lithologic discrimination of non coring wells. [ABSTRACT FROM AUTHOR]

The Precaspian Basin is a supergiant petroliferous basin around the world. A series of large-scale carbonate oil fields are developed in its eastern margin. In this paper, the characteristics of marine facies carbonate reservoirs in the Precaspian Basin are studied based on core observation and thin section analysis, combined with logging curve, high-pressure mercury injection, physical property analysis, and various test data. According to the macroscopic and microscopic lithologic characteristics from the coring well, the lithology in the study area is divided into six types: granular dolomite, crystal grain dolomite, other dolomites, granular limestone, crystal grain limestone, and other limestones. Three types of reservoir spacepores, vugs, and fracturesare developed. They include structural fractures, interlayer fractures, pressolutional fractures, and corroded fractures, greatly affecting reservoir properties. The diagenetic facies here can be divided into 4 types and 7 subtypes by sedimentary background, rock type combination, main diagenesis, diagenetic evolution, and pore association type. Diagenetic facies analysis for simple wells is implemented, and then the spatial distribution of the reservoirs is analyzed. As a result, this study provides a reference for the searching of high-quality reservoirs. [ABSTRACT FROM AUTHOR]