Tengiz and Korolev fields are giant, isolated carbonate platform reservoirs located in western Kazakhstan. Oil production in large regions of these fields is dominated by naturally formed fracture and karst cavern networks (i.e., nonmatrix). These networks around the fields are chiefly characterized using static logs, drilling data, and dynamic data from surveillance, as these data sets provide the most complete coverage through the three-dimensional reservoir volume. Core data sets, although significantly less in reservoir coverage, contain valuable ground truth information about the nonmatrix system that can be integrated into log-based interpretations. This study uses the extensive core data set available from Tengiz and Korolev to better understand the genetic origins, spatial distributions, and diagenetic evolution of the fracture–karst networks around the fields.

Documentation of Tengiz and Korolev natural fractures in core confirms the presence of both diagenetically early (syndepositional) and late (burial) fractures and reveals significant differences in their spatial distributions and attributes. Evidence in cored intervals adjacent to open karst caverns supports both early meteoric and late burial origins of karst cavern networks and supplement the largely log-based characterization. Core also reveals that the lower slope at Tengiz, a historically underperforming reservoir region, has comparable fracture presence to more productive regions, but was preferentially impacted by late-stage burial cementation that degraded fracture and karst network flow properties. These findings, only available from core, allowed for development of conceptual diagenetic models of the nonmatrix system and refinement of dynamic reservoir regions that link to production performance and provide inputs for reservoir modeling.