Modeling of Diagnostic Fracture Injection Tests (DFITs) for In-situ Stress Characterization in the Utah FORGE Reservoir

Abstract

Diagnostic fracture injection tests (DFITs) are used to estimate the minimum horizontal stress in a target reservoir through analysis of the pressure response during the controlled injection process. The in-situ stress condition inferred from DFIT tests is crucial for designing and optimizing the stimulation and circulation processes in enhanced geothermal systems (EGS). In this work, we employ a coupled finite-element/finite-volume numerical simulator to model DFITs in EGS settings. To better capture fracture closure, we integrate stress-dependent aperture models (e.g., the Barton–Bandis model and an exponential model fitted to experimental data) into an established hydraulic fracturing solver. Then, we apply the solver to history match the pressure data observed in the injection and shut-in activities in Zone 2 of Well 58-32 at the Utah-FORGE site. The fracture properties adopted in the model are referred to tri-axial direct-shear experiments on granite samples collected from the Utah-FORGE site. In the simulation, the thermal effects on DFITs responses are investigated by comparing predictions under isothermal and non-isothermal conditions. The findings from this numerical study provide insights into identifying in-situ stress conditions and the role of thermal processes in the Utah-FORGE reservoir.