Two‐Phase Relative Permeability of Rough‐Walled Fractures: A Dynamic Pore‐Scale Modeling of the Effects of Aperture Geometry.

An accurate description of the relative permeability–saturation function is crucial for reliable predictions of multi‐phase flow behavior in subsurface applications. Although extensive efforts have been put forth to investigate the relative permeability behavior in different types of porous media, only few studies have focused on rough‐walled fractures. In this work, we present an entirely new, cost‐effective, heavily‐parallelized, dynamic pore‐network modeling framework that is employed to conduct a systematic study of relative permeability curves under two‐phase flow conditions in rough‐walled fractures. We first build a two‐dimensional (101.42 × 24.86 mm2) equivalent pore network of a Berea sandstone fracture from its x‐ray images. Subsequently, dynamic primary drainage and imbibition simulations are conducted in the fracture. We show that the two‐phase fluid occupancy maps predicted from the simulations agree well with the fracture fluid configurations obtained via X‐ray computed tomography. Afterward, the validated model is used to probe two‐phase flow properties in a series of synthetic aperture fields generated with a broad range of geometric characteristics including aperture spatial correlation length (normalized correlation length varying from 0.05 to 0.95), anisotropy factor (0.25–4), surface roughness (normalized fracture roughness varying from 0.05 to 0.4), and mean aperture size (50–800 μm). The generated results provide novel insights into the effects of these features on two‐phase flow properties such as fluid–fluid interfacial area, phase interference, and relative permeability. Moreover, based on the simulation results we propose two new correlations to describe the relative permeability curves for primary drainage and imbibition processes in rough‐walled fractures. Plain Language Summary: Modeling two‐phase flow in rock fractures still remains a challenge because of the highly irregular geometries of the rough‐walled fractures. For example, there is still no consensus regarding how two‐phase flow properties behave in a single fracture. To address this problem, we developed a new dynamic pore‐scale modeling platform. It rigorously solves for the forces associated with two‐phase displacements in fracture spaces and has an advantage of being computationally efficient. As a result, we are able to conduct a comprehensive and systematic study of two‐phase flow properties in a large number of synthetic fractures designed with varying geometric features. The generated results not only significantly improve the understanding of the effects of the aperture geometries on the two‐phase flow properties but also allow us to propose new correlation equations describing fluid flow properties of rough‐walled fractures that can be directly adopted for use in predicting flow behaviors in fractured media at the large scale (meters to kilometers). Key Points: A new, computationally efficient, dynamic pore‐network model for two‐phase flow in rough‐walled fractures is developed and validatedImpacts of correlation length, aperture anisotropy, fracture roughness, and aperture size on fracture relative permeability are studiedNew relative permeability models are proposed for drainage and imbibition processes in rough‐walled fractures [ABSTRACT FROM AUTHOR]