ABSTRACT

Micropores can constitute up to 100% of the total porosity within carbonate-hosted hydrocarbon reservoirs, usually existing within micritic fabrics. Here, three-dimensional computational representations of end-point micritic fabrics are produced using a flexible, object-based algorithm to further our understanding of the contribution that micropores make to flow. By methodically altering model parameters, we explore the state space of microporous carbonates, quantifying single and multiphase flow using lattice-Boltzmann and network models.

In purely micritic fabrics, average pore radius (ranging from 0.26 to 0.44 μm) was found to have a positive correlation with single-phase permeability (1.7 to 2.7 md, respectively). Similarly, increasing average pore size resulted in decreasing residual oil saturation under both water-wet and 50% fractionally oil-wet states. Permeability was found to increase by an order of magnitude (from 0.6 to 7.5 md) within fabrics of varying total matrix porosity (from 18% to 35%) because of increasing pore size (0.37 to 0.56 μm, respectively), but minimal effect on multiphase flow was observed. Increased pore size due to micrite rounding notably increases permeability in comparison with original rhombic fabrics with the same porosity, but multiphase flow properties are unaffected.

Finally, when moldic mesopores are added to a micritic matrix, they impact flow when directly connected. Otherwise, micropores control single-phase permeability magnitude. Importantly, recovery is dependent on both wetting scenario and pore-network homogeneity: under water-wet imbibition, increasing proportions of microporosity yield lower residual oil saturations.

Together, these results quantify the importance of micropores in contributing to, or controlling, overall flow and sweep characteristics in such fabrics.

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