Experimental and Numerical Study of Hydraulic Fracturing in Enhanced Geothermal Systems (EGS)

Abstract

Enhanced Geothermal Systems (EGS) rely on hydraulic fracturing to enhance the hydraulic conductivity of nearly impermeable subsurface formations. The propagation patterns of hydraulic fractures and their reactivation are dictated by several factors, such as rock heterogeneities, temperature variations, and in-situ stress magnitude and orientations. Thus, to perform effective stimulation and ensure long term performance of EGS, it is crucial to understand the influence of these factors on the hydraulic fracturing process. In this work, we present initial results from a combined experimental and numerical study of near-wellbore hydraulic fracture propagation. The laboratory investigation entails a series of hydraulic fracturing experiments on cold spring granite samples under a true triaxial stress condition, in which we can obtain the breakdown pressure, fracture geometry, and re-opening pressure. These experimental results are used to calibrate a phase-field numerical model for hydraulic fracture initiation and propagation. The calibrated model is then employed to explore the effect of the in-situ stress on the hydraulic fracturing process. The outcome of this combined study is believed to advance our understanding of the reservoir-scale hydraulic fracturing process in EGS.