A Well Log Identification Method of Complex Carbonate Reservoir Lithotypes and Lithofacies: A Case Study on Formation Unit B in K Oil Field, Caspian Basin, Kazakhstan

Abstract Based on cores lab data observation, depositional facies analysis, lithotypes analysis and well logging data, the characteristics of lithotypes and lithofacies of carbonate reservoirs Carboniferous Unit B formation of K oil field in the southern margin of Kazakhstan Caspian basin are described and summarized, the identification standards of lithotypes and lithofacies by using well logging are established. The main lithofacies in Unit B formation carbonate reservoir were classified into 6 types: compacted limestone, grainstone, reef limestone, wackestone/packstone, marlstone and mudstone. The lithotypes and lithofacies in Unit B formation in K oil field were analyzed both qualitatively and quantitatively by conventional logging and imaging logging and other methods. The discriminatory criteria of reservoir lithotypes and lithofacies were established by analyzing conventional logging and imaging logging data, summarizing the different facies lithology logging response characteristics, developing carbonate lithology structure index(CLSI) characterizing its quantitative characterization. In this study, the depositional facies were analyzed: two main depositional environments developed in K field, which are platform and slope, and the dominant facies in this block can be divided into lagoon, tidal flat, intershoal depression, rim shoal, rim reef, the outer continental shelf and continental slope. The well log responses of each lithology and lithofacies were identified, the five different types were recognized by the above method. The identification and classification of lithotypes and lithofacies in both vertical and horizontal disturbition in UnitB formation were achieved by processing the logging data from each well in this block, the identification results of lithotypes and lithofacies were well matched the analysis of physical properties. This study is one of the important keys for the reserves calculation and the development plan, and also guides to evaluate the complex carbonate reservoir of K oil field.