Normal Deformation and Formation of Contacts in Rough Rock Fractures and Their Influence on Fluid Flow

摘要

Rock fracture flow was initially modeled according to the parallel plate model, which does not consider the undulating nature of fracture surfaces. The conventional parallel plate model or cubic formula was later modified to obtain precise predictions by considering the joint roughness coefficient (JRC) of the fracture walls. However, the real flow characteristics through a relatively long rough rock joint can still be modeled accurately via a two-dimensional analysis, which enables the spatial irregularity of rock fracture apertures to be considered with the fracture contacts, which act as obstacles to the flow. In this study, a new two-dimensional flow model for deformable fracture walls to predict the volumetric flow changes that result from effective normal stress fluctuations is proposed. This model was solved using the finite-volume method via a new program developed by the authors. It captures the existing contacts and newly formed contacts that occur while fracture aperture deformations take place and treats them as local boundaries. The model flow-rate predictions were compared with the simulated real rock fracture flow carried out on a high-pressure two-phase triaxial apparatus (HPTPTA) designed and built at the Univ. of Wollongong (Wollongong City, Australia). The model predictions and experiment results of volumetric flow rates were in good agreement, which verifies the accuracy of incorporating a more realistic contact treatment process between the upper and lower asperities during joint closure. The numerical simulations illustrate flow paths within the rock fracture in a more realistic manner without having to consider the entire fracture surface to be permeable.