Slope systems flanking high-rising isolated carbonate platforms and dominated by "deep-reef" microbial boundstone are heterogeneous due to a spectrum of depositional processes that cause a high degree of vertical and lateral variability. In addition, they are conceptually complex as a result of their poorly understood depositional controls and insensitivity to sea level fluctuations.

The nature of the margins and slopes of the giant carbonate reservoirs of the Pricaspian Basin remains a controversial topic. Among the reasons is the poor quality of seismic data due to overlying salt as well as the lack of depositional models explaining their spatial distribution and seismic response. The use of analogs, in particular those from the Carboniferous of Spain, the Permian of New Mexico and Texas (USA), the Devonian of the Canning Basin (Australia), and the Triassic of the Dolomites (Italy), provide highly valuable depositional models.

Intact and seismic-scale outcrops in northern Spain, USA and Italy proved the existence of deep-reef microbial boundstone slopes that characteristically display high progradation rates, propensity for fracturing and collapse, and insensitivity to sea level. Cores from the Tengiz and Karachaganak fields, when tied with reflection terminations and log character, confirm the presence of such slopes, leading to a radical change in the depositional and reservoir models. Results from the Canning Basin and Permian Basin provided models for margin styles and the detrital portions of slope systems that were successfully applied to portions of the fields. Seismic geomorphology and stratigraphic interpretation, guided by understandings from outcrops, allowed for the subdivision into multiple styles of clinoforms, slope and basin sediment wedges, margin configurations, and secondary features (i.e. reentrants). These revised subdivisions better conform to and explain the observed trends in reservoir properties and connectivity of the fields.

Thus, integration of depositional models derived from outcrop analogs with seismic facies analysis, cores, log character and static and dynamic data is a critical step in reducing uncertainty and improving reservoir characterization, especially in cases where seismic response is obscured and well data is limited.

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