Study on Carbonate Reservoir Characteristics and Their Impact on Oilfield Productivity: A Case Study of the Karabulak Oilfield, Kazakhstan

The Karabulak Oilfield in Kazakhstan’s South Turgay Basin is characterized by complex reservoir lithology and diverse storage space types, which complicate the identification of favorable reservoirs and obscure the distribution characteristics and productivity impact of fractures. Despite these challenges, the region holds enormous potential for residual hydrocarbon resources. This study employs a hierarchical calibration approach, integrating core analysis, conventional well logging, and 2D seismic data, with an emphasis on optimizing sensitive curves and parameters. The primary reservoir lithologies are systematically classified as limestone, bioclastic limestone, breccia limestone, and argillaceous limestone, while the storage space types are categorized into framework type, fracture-pore type, and fracture-karst breccia type. Based on oil testing and trial production analysis, the reservoirs are further subdivided into Classes I, II, and III, and their distribution zones are delineated as corresponding to the bioclastic limestone, fractured limestone, and argillaceous limestone with karst breccia development areas, respectively. Notably, fractures are predominantly developed near the northern fault belt in the central area, serving as the major contributor to field productivity. This study provides a novel approach for analyzing reservoir characteristics and delivers robust geological evidence for optimizing hydrocarbon exploration in similar carbonate systems.