Examining fluid flow and solute transport through intersected rock fractures with stress-induced void heterogeneity

Abstract

In this study, fluid flow and solute transport processes are assessed in three-dimensional (3-D) intersected rock fractures with stressed-induced void heterogeneity. Specifically, flow behaviors are examined in the intersected fractures with flow directions perpendicular and parallel to the intersection orientation. Then, transport behaviors are analyzed considering the classic continuous flow condition, and a new mixing ratio is proposed to better quantify the mixing process. Last, applicability of two-dimensional (2-D) representations of rock fractures for analyzing flow and transport is assessed by result comparison with the 3-D cases. The results show that fracture intersecting can enhance transmissivity of the single fracture as a result of locally enlarged aperture at the intersection and generation of more conducive flow paths, with latter being the main mechanism especially when under high stress. Moreover, it is found that transport behaviors can differ evidently in intersected fractures due to stress-induced void heterogeneity and anisotropy. For intersected fractures with obvious directional void heterogeneity, solute transport can become more nonuniform with occurrence of forced mixing caused by scattered flow channeling from the intersection. Compared to the actual 3-D cases, adopting the 2-D representations is generally found to produce transmissivity overestimation and mixing underestimation, due to inaccurate quantification of the 3-D flow and transport features. Considering the realistic stress-induced void heterogeneity for rock fractures, the findings of this work can further broaden our understanding of the flow and transport processes in underground fractured rock formations.