Estimating the Utah FORGE Reservoir State of Stress Using Differential Strain Curve Analysis Method

ABSTRACT: Knowledge of the in-situ stress state at the Utah Forge (Frontier Observatory for Research in Geothermal Energy) site is critical for geothermal energy exploration and development. This study employs a strain recovery method: Differential Strain Curve Analysis (DSCA) to provide estimate of the reservoir stress state at different depths. The Differential Strain Curve Analysis (DSCA) method focuses on the differential strains that result from microcrack closure under varying stress conditions, particularly during hydrostatic loading. As the rock sample undergoes stress changes - such as during unloading or pressure cycling the differential strains, which are the differences in strain measured along different axes, change due to factors like microcrack closure and elastic deformation. These strain variations provide insights into the material's stress history and help assess the directional distribution of the principal stresses within the rock, revealing how the original in-situ stress field influences the rock's response. This method is applicable in borehole-based and laboratory testing environments, making it versatile for field studies and core sample analysis. Utilizing high-quality granitoid core samples from various depths, initial findings suggest a nearly vertical maximum principal stress indicative of an extensional regime controlled by normal faulting. These results are consistent with the stress data obtained from wellbore breakouts, drilling induced cracks and minifrac tests. Additional testing is ongoing to further elucidate the stress regime and investigate potential influences. This integrated approach enhances our understanding of the stress state at the Utah FORGE site and its implications for wellbore stability and geothermal resource management, contributing valuable data for future geodynamic studies.