High-Resolution Fluid Flow Simulation in X-Crossing Rough Fractures

Abstract

ABSTRACT Modeling of fluid flow in rock fractures is a key issue in answering numerous geoengineering problems in the fields of geophysics, reservoir engineering, rock mechanics, to geothermal processes. Although fluid flow in single fractures has been extensively studied in the last 7 decades, fractures commonly seen in fractured reservoir systems intersect each other forming complex geometric structures. Such fracture networks likely affect fluid flow behavior and solute transport. To investigate the impact of geometric characteristics of connected rough-walled fractures with an X junction shape on linear and nonlinear fluid flow behaviors, a sensitivity analysis was carried out by conducting a series of numerical fluid flow simulations on X shape fractures, generated by scanning real rock fractures with distinct roughness (low, medium, and high), intersecting angles, and apertures. The fluid flow through these fractures at different flow rates was simulated by solving Naiver-Stokes equations. The results show that tortures paths and the formation of eddies are more accentuated on the rough fracture than the smoother ones, and the tortuosity of the streamlines is related to the roughness and the geometric characteristics of the intersection. Simulation results of the different models were compared, which show that the intersection significantly impacts the relationship between the hydraulic gradient and the flow. Therefore, the pressure gradient increases with the decrease of the intersection angle especially for low aperture and rough cases. INTRODUCTION Understanding fluid flow through a fractured rock mass has great importance to numerous underground industrial activities, such as geothermal extraction (Zhao, 2016), CO2 storage (Catherine Noiriel et al., 2013), oil and gas exploration (Bo Li et al., 2016), underground oil storage (Qiao et al., 2017; Wang et al., 2015), and hydraulic fracturing (Blanton TL,1982). It is important to measure the impact of roughness to improve the performance of large-scale models since most existing large-scale models still rely heavily on simplified smooth parallel-plate models and related models for natural rock fractures with rough walls (Zimmerman et al., 1992; Zimmerman and Bodvarsson, 1996; Ge 1997; Bodin et al., 2007; Zhao et al., 2013; Wang et al., 2015).