Implications of Local‐Scale Approximations on Describing Fluid Flow in Rock Fractures With Stress‐Induced Void Heterogeneity

Abstract

AbstractStudies on discrete fracture network models have recently shown progress by incorporating aperture heterogeneity to individual fracture elements for more accurate description of flow‐related processes in subsurface fractured rocks. Compared to a more realistic account of fracture‐scale void heterogeneity, the standard Reynolds equation (RE) is mostly adopted as the flow governing equation despite its inaccuracy described in many previous studies. To find effective models for flow in rock fractures under realistic subsurface stresses with proper knowledge of the associated uncertainties, we test four conceptual flow models with incorporation of five local‐scale approximations in rock fractures with varying stress‐induced void heterogeneity. From the analysis, we show that the parallel‐planar plate local‐scale approximation in the standard RE can lead to both overestimation and underestimation of the local flow due to the defect of the aperture‐averaging approach. In general, higher local deviations are observed for slow‐flow regions in the fracture void for all tested local‐scale approximations, whereas the faster‐flow regions are responsible for the overall deviation of the predicted fracture transmissivity. Among the tested local‐scale approximations, two of them are found to evidently improve the standard RE in terms of describing the local velocity field and estimating the overall fracture transmissivity, with absolute mean deviations of ∼11% and ∼7%, respectively. The results from this work further confirm improved flow estimation for subsurface stressed rock fractures by incorporating more accurate local‐scale approximations.