Effect of multi-scale rough surfaces on oil-phase trapping in fractures: Pore-scale modeling accelerated by wavelet decomposition

Ignoring the surface roughness of fractures can lead to a significant overestimation of reservoir recovery. We quantitatively investigated the oil-phase trapping mechanism using pore-scale modeling to calculate two-phase fluid flow in a single fracture with multi-scale rough surfaces. On this basis, we propose an accelerating modeling method combining wavelet decomposition and a correction function to enhance computational efficiency without compromising the accuracy of the residual oil. Our results indicate that the kinetic energy of the oil-phase flow driven by CO₂ is gradually converted into pressure energy, which overcomes the oil-phase surface energy and causes the oil-phase to become trapped in some grooves on the rough fracture. Even structural details of 0.05 µm have non-negligible effects on the residual oil volume, which can be quantified using the proposed correction function. In such cases, the residual oil can be calculated accurately if the wavelet decomposition is not higher than the fourth level, where structural details of < 1.0 µm can be ignored. Computational efficiency can be enhanced six-fold when using the wavelet decomposition of the fourth level. The accelerated modeling method presented herein provides an effective representation of multiphase flow dynamics in rough fractures and offers a feasible solution for cross-scale calculations.