Investigating the Impact of Stratigraphic and Sedimentological Heterogeneities on Flow in Carbonate Reservoir Models, Using a Hierarchical Approach with Experimental Design

Understanding and predicting the production behaviour of carbonate reservoirs is challenging due to the impact of heterogeneities that occur at all scales that cannot be readily captured in conventional reservoir models and workflows. Much of this heterogeneity can be attributed to variability in stratigraphic architecture, complex geobodies, depositional facies, lithology, mineralogy, pore type, and pore connectivity. These heterogeneities can occur across numerous length-scales, and different heterogeneities may act individually or in combination to impact fluid flow in reservoirs.

We have developed a hierarchical classification scheme of stratigraphic and sedimentological heterogeneities in carbonate reservoirs. At the large scale (1-10s km laterally, 1-100s m vertically), our hierarchy of heterogeneity contains gross stratigraphic architectures, broad environments of deposition, and major discontinuity surfaces. The medium-scale hierarchy (10-1000 m laterally, 0.1-10s m vertically) focuses on depositional facies distribution within stratigraphic units, the nature of facies boundaries, and lateral variations in the character of discontinuity surfaces. Small-scale heterogeneities (<100 m laterally, <1 m vertically) include bed geometries within depositional facies and diagenetic features within individual beds. Heterogeneity at centimetre-to-micrometre scale (e.g. sedimentary structures, grain shapes, pore networks) is not explicitly represented in our models, although their effects are represented by effective rock properties within model grid blocks.

This scheme is used to identify end-member examples of appropriate key heterogeneities. Conceptual models are constructed, based on project-specific outcrop analogue, forward model and published examples, which are incorporated into high resolution models. Models are constructed using a combination of conventional and surface-based modelling techniques, which enable accurate and efficient capture of heterogeneity geometries. Flow simulation of a series of “nested” models at different length scales, combined with experimental design techniques, enables the key controls on reservoir performance to be identified and their impact on hydrocarbon recovery to be quantified for a range of production mechanisms and fluid types.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California