Quantifying flow in variably wet microporous carbonates using object-based geological modelling and both lattice-Boltzmann and pore network fluid flow simulations

Micropores can constitute up to 100% of the total porosity within carbonate hosted hydrocarbon reservoirs, usually existing within micritic fabrics. Here, 3D 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 multi-phase flow using lattice-Boltzmann and network models.

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