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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

Evaluating Fundamental Controls from Depositional Facies Heterogeneity in a Carbonate Ramp Using Forward Stratigraphic Modeling

Miriam S. Andres1; Paul M. Harris1; Gareth D. Jones1

(1) Chevron Energy Technology Company, San Ramon, CA.

Much of our understanding of the depositional facies heterogeneity, to date, derives from geological concepts, outcrop studies and subsurface information. Deposited strata represent the unique solution to a combination of fundamental controls at the time, not including subsequent diagenetic, tectonic and/or burial overprint. Forward stratigraphic modeling (FSM), in contrast, provides an opportunity of simulating multiple solutions by isolating one of the fundamental controls. In this capacity we use the FSM tool ‘Dionisos’ to investigate the role of various input parameters and their control on a grain-dominated carbonate ramp setting typical of the Middle East. Specifically, we focused on extent and distribution of reservoir and non-reservoir facies as they are key to understanding and predicting reservoir connectivity and potentially performance in carbonate ramps.

Our base-case model comprised several ~4th-order sea-level fluctuations, variable subsidence, carbonate production (ooids, peloids, carbonate mud), and shale parameters. Transgressive surfaces, often mud-dominated, are an important element in ramp systems as their up-dip extent and thickness offer potential for compartmentalization and barrier to flow. Hence, we simulated system tracts comprising a mud-dominated initial early transgression, and a middle-late transgression characterized by the onset of ooid production peaking in the early highstand.

Sensitivity analysis focused on varying ooid production rates, their production as a function of water depth. In the latter, extending the depth production profile (from 5 to 7 to 9 m) impacted volume (tripled at 9 m) and extent of the ooid facies (i.e. 8 km of increased progradation). Likewise, the shape profile, straight vs. gradual decline to zero production, impacted clinoform thickness and basin-ward extent as accommodation space is filled such that the ensuing sequence encounters an even increased modeling window resulting in subsequent thicker sequences and faster progradation. By setting sediment erosion and low-energy transport rates to zero we evaluate the amount of in-situ production vs. transport. Our simulations suggest that down-dip transport and erosion are key, yet underappreciated in understanding reservoir-prone facies connectivity.