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Multi-Scale Flow Modeling of Heterogeneous Carbonates

Zhang, Tuanfeng 1; Hurley, Neil F.1; Zhao, Weishu 1
1 Schlumberger-Doll Research, Cambridge, MA.

Carbonate reservoirs have pore sizes that range over at least six orders of magnitude, and they have complex depositional facies and diagenetic textures. Reservoir engineers have struggled for decades to measure residual oil saturations, wettabilities, effective permeabilities, and relative permeabilities in such heterogeneous reservoirs. This study bridges the gap between cores, borehole images, and flow simulations in complex carbonate reservoirs.

Numerical pseudocores provide a new, state-of-the-art method to help solve the problem of carbonate reservoir heterogeneity. Numerical pseudocores are three-dimensional (3D) computer models of rocks and pores, generated from borehole images and digital rock samples, such as conventional computed-tomography (CT) scans, using multi-point statistics (MPS). Integer values are assigned to each petrophysical facies, for example, dense rock matrix (0), vugs (1), and conductive patches (2). Digital rock samples are used as training images, that is, they are the quantitative templates used to guide the modeling of 3D textures in the pseudocores. Borehole images surround numerical pseudocores with cylindrical envelopes that condition the models. Each numerical pseudocore absolutely honors the heterogeneities observed in digital rock samples and borehole images.

For each petrophysical facies, capillary pressure and relative permeability curves are provided by conceptual models, special core analyses, or pore-network models at micron-scale resolution. Effective or bulk properties, such as residual oil saturations and relative permeabilities, can be computed by running multiphase flow simulations through numerical pseudocores. Such properties are essential to constrain interwell or field-scale flow simulations. Additionally, the numerical pseudocore workflow quantitatively evaluates recovery factors in carbonate rocks.

 

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