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Sedimentary Architecture of a Lower Carboniferous Carbonate Platform through Stratigraphic Forward Modeling, Kashagan Buildup (Kazakhstan)

Casaglia, Francesca 1; Claps, Michele 1; Zempolich, William G.1
1 Agip KCO, San Donato Milanese, Italy.

3D stratigraphic forward modeling is a powerful technology used at reservoir scale to improve confidence in building geomodels and in predicting facies distribution and architecture. Furthermore such models can be used to better constrain the interpretation of subsurface data and to perform sensitivity on sedimentological parameters controlling a proved stratigraphic framework. This proves to be critical for carbonate systems since their intrinsic complexity can generate uncertainties in their subsurface interpretations and evaluations.

Here we have adopted a sensitivity analysis and a trial/error approach, using the process-based forward model Dionisos, developed by Institut Français du Pétrole, to investigate the sedimentary response of the Kashagan platform, an isolated Lower Carboniferous carbonate buildup, located in the Southern margin of the Pre-Caspian Basin. Kashagan is a supergiant reservoir with a complex sedimentological and stratigraphic framework.

The depositional model generated by Dionisos focuses on simulating the 3D stratigraphic architecture at third order scale and creating a lithological model that merges seismic-scale interpretations with sub-seismic scale well data. The Kashagan forward model has been built through integrating all the available geological information and the conceptual stratigraphic framework.

Each simulation is controlled by processes which create accommodation space (such as eustatic sea-level variation, subsidence and sub-aerial dissolution) as opposite to others which result in infilling the generated space (carbonate productivity as a function of time, water depth and wave energy) or transporting sediments within the depositional system (wave-driven and gravity-driven transport mechanisms). Seven lithological components have been defined and distributed in the model according to these geological parameters. Accommodation space maps have been defined at each major sequence boundaries taking in account the synsedimentary tectonic features and the layer stacking derived from seismic and well interpretations.

The 3D simulated depositional lithofacies have been used to improve the pre-existing Environment of Deposition model generating a high-resolution EoD framework for each individual 3rd order sequence and depositional environment lateral shifts.

The resulted 3D model has been also exported in the reservoir static models as facies maps for each main stratigraphic layer.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009