A new approach for two-phase rock typing: Evaluation with pore network simulations

Abstract:

Rock typing plays an important role in petroleum engineering, particularly in reservoir characterizations. Although classifying rocks based on single-phase flow properties has been extensively developed in the literature, rock typing based on two-phase flow characteristics is still very limited. This is important because rock typing using single-phase flow properties ignores the effect of contact angle and in turn, wettability, and thus it cannot differentiate rocks with similar characteristic pore sizes but distinct contact angles and wettability. In this study, we aim to address this knowledge gap by classifying reservoir rocks using a new theoretical rock-typing approach based upon critical path analysis and two-phase flow measurements, such as water relative permeability curves. To evaluate our approach, we generated a large dataset using a wide range of rock properties and a variety of pore-throat size distributions, contact angles, pore coordination numbers, and residual water saturations. Using pore-network simulations, water and oil relative permeability and capillary pressure curves, the formation factor, and single-phase permeability were computed. For rock typing, we first determined the critical pore-throat radius, r_c(S_w), at various water saturations for each sample. We then plotted r_c(S_w)/r_c(S_w = 1) against the effective water saturation, S_e, and clustered the curves that collapsed together. The results indicate two main rock types and several subgroups. The two identified main rock types were based primarily on two ranges of the pore throats’ sizes used to generate the pore networks. Further investigations are required to evaluate the proposed two-phase rock typing approach with experimental measurements.