Laboratory Investigation of Fracture Behavior and Roughness Evolution in Simulated Hydraulic Shear Stimulation for Enhanced Geothermal Systems (EGS)

Enhanced Geothermal Systems (EGS) utilize artificially induced fracture networks to enable fluid circulation and heat extraction from high-temperature, low-permeability geological formations. Unlike conventional hydraulic fracturing in the hydrocarbon industry—which commonly employs proppants to keep fractures open—EGS stimulation primarily relies on hydraulic shear stimulation. This technique leverages the self-propping behavior of pre-existing fractures, eliminating the need for proppants. To replicate hydraulic shear stimulation in a controlled laboratory setting, we conducted shear-flow experiments on various fracture types, including shear fractures, tensile fractures, and saw-cut fractures. Most previous studies have focused on tensile and saw-cut fractures, typically treating them as idealized representations of smooth or rough fracture surfaces. However, shear fractures—due to their naturally formed characteristics—offer a more realistic simulation of in-situ conditions and better represent pre-existing fractures in the field. To evaluate fracture surface roughness, we employed a 3D laser scanner. The digitized surface data, captured both before and after the shear-flow tests, were recorded in .CSV files for subsequent analysis.