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

Chalky microporosity can constitute up to 100% of the total porosity within carbonate reservoirs, but its contribution to both single- and multi-phase flow is poorly quantified. We present a flexible, object-based algorithm to construct 3D computational rock representations that reproduce micritic fabrics of chalky microporous carbonates based on calcite crystal fabrics observed in 2D SEM images. By methodologically altering model parameters we begin to explore the state-space of microporous carbonates to quantify single- and multi-phase flow using both lattice-Boltzmann and network flow models.
Micropore size has little to no effect on single-phase permeability, while differences in multi-phase flow properties are observed for microporous fabrics with pores no smaller than 0.50μm3 suggesting a change in the pore-scale controls on flow. Single-phase permeability increases by an order of magnitude within fabrics of varying total microporosity (18% to 35%), but minimal effect on multi-phase flow is observed. Similarly, multi-phase flow properties are unaltered by micrite rounding due to burial dissolution, suggesting no alteration in pore-network topology. Micrite rounding, however, notably increases porosity and single-phase permeability in comparison to original rhombic micrite fabrics. The presence of moldic mesopores impacts flow but only when there is a direct connection between them. Otherwise, single-phase permeability is controlled by
micropores. Importantly, recovery is dependent on wetting scenario and pore-network homogeneity. Under water-wet imbibition, an increase in pore homogeneity (more micropores) yields a lower residual oil saturation. Together, these results quantify the importance of microporosity in contributing to, or controlling, overall flow and sweep characteristics in carbonate reservoirs.