- EGS STIMULATION DE-RISKING STRATEGY

IDENTIFICATION OF A SHALLOW MECHANICAL “SWEET SPOT” IN THE UTAH FORGE GRANITOID USING INTEGRATED PETROPHYSICAL ANALYSIS

Abstract

High confinement stress and ductile failure modes frequently hinder the formation of complex fracture networks in deep Enhanced Geothermal Systems (EGS). This study proposes an operational de-risking strategy by characterizing the shallow transition zone at the Utah FORGE site. Integrating dipole sonic logs and drilling parameters from pilot well 58-32 and offset well 16A(78)-32, we applied robust P10-P90 statistical normalization to identify a mechanical "sweet spot." A highly brittle interval was defined at 3,892 ft (Brittleness Index > 0.82; Young’s Modulus > 75 GPa). Lateral validation in the offset well confirms regional continuity, evidenced by spectral uranium anomalies (> 3 ppm) and distinct drilling breaks (MSE drop < 20 kpsi), indicating a permeable natural fracture corridor. In sharp contrast to the semi-ductile deep reservoir (> 7,000 ft; BI < 0.46), this shallow brittle interval offers an optimal, lower-risk candidate for Diagnostic Fracture Injection Tests (DFIT) to calibrate stimulation parameters before targeting the high-risk deep basement.