A Hierarchical Approach to Characterizing the Impact of Stratigraphic and Sedimentological Heterogeneities on Flow in Carbonate Reservoirs

Fitch, Peter J.¹; Jackson, Matthew D.¹; Hampson, Gary J.¹; John, Cédric M.¹
(1)Department of Earth Science and Engineering, Imperial College London, London, United Kingdom.

Carbonate reservoirs contain over 60% of the world’s remaining oil reserves and 40% of gas reserves. Understanding and predicting their production behaviour 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, depositional facies, lithology, mineralogy, pore type, and pore connectivity. These various parameters can be related to carbonate depositional environments and subsequent diagenesis.

We have applied a hierarchical approach to characterizing sedimentological and stratigraphic heterogeneity in carbonate reservoirs, as a basis to investigate their impact on fluid flow and recovery via flow simulation of reservoir models. 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.

We are using the hierarchy of heterogeneity to guide the construction of reservoir models of generic carbonate reservoirs at a range of appropriate length scales, starting with the largest scale of the hierarchy and then moving to progressively smaller length scales. 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 #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.