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Integrated Characterization of a Steep-Sided Isolated Carbonate Platform Reservoir, Tengiz Field, Kazakhstan


Tengiz Field is a Devonian-Carboniferous isolated carbonate platform reservoir in the southern Pricaspian Basin, western Kazakhstan, which constructed over 1 km of shelf-to-basin relief with steep (up to 50o) margins and slopes during its evolution. A significant fraction of the field's 26 billion bbls of oil in place and high productivity zones reside in the steep margins and slopes of the buildup, however reservoir performance prediction is difficult in part due to extreme depositional variability. This heterogeneity is linked to a spectrum of deposit types, variations in margin style along strike, complex spatial architectures, and temporal changes in margin trajectories. Integration of 3D seismic, core, image logs, and chronostratigraphic approaches improved platform-to-slope correlations, facies distribution mapping, and conceptual models to better characterize the stratigraphic and geographic depositional variability around the field. An integrated chronostratigraphic approach [combining biostratigraphy, magnetostratigraphy, chemostratigraphy, and sequence stratigraphy] provided robust correlation constraints to update the seismically-driven stratigraphic framework. Facies interpretation from image logs, calibrated to core and validated, added significant rock-based control at wells. Seismic geometries and characteristics, when calibrated to image log and core facies interpretations, allowed for mapping of depositional regions away from well control. Products of this integration are modified and new conceptual models around Tengiz Field that better capture: 1) spatial and vertical changes in the proportions of boundstone, debris, grain-dominated, and mud-dominated slope deposits; 2) km-scale, along-strike margin variations ranging from erosional escarpments with onlapping slope wedges to clinoformal accretionary configurations; 3) multi-km margin reentrants generated from large-scale failure; 4) discrete isolated geobodies and their distributions; and 5) the timing and extents of margin progradation. These concepts and the improved stratigraphic framework and facies control around Tengiz provide the basis for first-order reservoir regions to assess diagenetic overprint and production characteristics within. The ultimate integrated results, including petrophysical rock types that encapsulate depositional and diagenetic controls on flow, will serve as input for the next generation static reservoir model of Tengiz Field.