Numerical investigation of the influence of discontinuity orientations on fault permeability evolution and slip displacement

Abstract

A pre-existing plane of weakness along the fault is comprised of a particular pattern of joints dipping at different orientations. The fault stress state, partially defined by the orientation of fault, determines the potential of slip failure and hence the evolution of fault permeability. Here the influence of fault orientation on permeability evolution was investigated by direct fluid injection inside fault with three different sets of fault orientations (45°, 60° and 110°), through the coupled hydromechanical (H-M) model TOUGHREACT-FLAC3D. The influence of joints pattern on slip tendency and magnitude of potential induced seismicity was also evaluated by comparing the resulted slip distance and timing. The simulation results revealed that decreasing the dip angle of the fault increases the corresponding slip tendency in the normal fault circumstance. Also, with changing joints dip angle associated with the fault, the tendency of the fault slip changes concurrently with the permeability evolution in a noticeable manner. Permeability enhancement after the onset of fault slip was observed with the three sets of fault angles, while the condition of 60° dipping angle resulted in highest enhancement. Joints pattern with a dip angle of 145° (very high dip) and 30° (very low dip) did not trigger a shear slip with seismic permeability enhancement. However, high dip and intermediate dip angles (135°, 50° and 70°) yielded high permeability in varying orders of magnitude. The large stress excitation and increasing permeability during shear deformation was noticeably high in intermediate joint dip angles but decreases as the angle increases. Article highlights The magnitude of injection-induced permeability enhancement is largely influenced by the fault and joint spatial orientations. With a slight change in the joint direction, there is an increasing possibility for fault to approach a different critical state of failure. Stress elevation at the point of failure is controlled by the orientations of fault/joint planes with respect to the direction of maximum principal stress.

Analysis of the influence of joint direction on production optimization in enhanced geothermal systems

“…Notably, the change in fault permeability following the shear failure on the fault plane vary in timing and magnitude as the fault geometry and the injection position change. An observation which has been established in this study and previous reports (e.g., Eyinla et al 2020Eyinla et al , 2021a. However, because the injection-induced permeability provides a pathway through which migration of fluid can occur, the production rate is expected to be directly related to the injection-induced permeability.…”

“…The fault is modelled as a ubiquitous fractured media, which accounts for the presence of an orientation of weak planes in a Mohr-Coulomb model (Cappa and Rutqvist 2011). However, this ubiquitous fault-joint model can assume distinct orientations, and their influence on the injection process in terms of permeability enhancement and magnitude of injection-induced seismicity have been fully discussed in previous reports by Eyinla et al (2021a), and .…”

“…Hence, knowledge of the variations in these properties is fundamental in characterising fractured reservoirs because they possess a direct correlation with the magnitude of fracture opening and production rate (Men et al 2018). The poroelastic effect caused by pressure build-up varies as the injection condition changes; consequently, when injecting into a low-permeable fault and fluid pressure is induced, the hydraulic diffusivity of the fluid pressure would be dependent on several factors such as the position of the injector, and the velocity of fluid transmission (Vilarrasa et al 2016;Eyinla et al 2020Eyinla et al , 2021aEyinla 2021;. However, the joint direction has been described as one of the factors which influences the instability of a fault and determines the fault reactivation potential and the rate of stress change during fault loading (Streit and Hillis 2004;.…”

Development of an Improved Decision Support Tool for Geothermal Site Selection in Nigeria Based on Comprehensive Criteria

“…The authors of ref. [45] reflected on the importance of geothermal resources and how the resources, if tapped, would address the electricity issues of Nigeria. The author of ref.…”