Flow path interpretation from DAS moment tensors applied to the Enhanced Geothermal System at Utah FORGE

Abstract We investigate moment tensor solutions of microseismic events observed during the 2023 circulation tests at the Utah Frontier Observatory for Geothermal Research (Utah FORGE). The microseismicity was recorded using two distributed acoustic sensing arrays located in separate wells, one of them the production well. Although the moment tensor inversion is ill-conditioned for most of the observed seismicity, there is a small group of events for which reliable solutions could be estimated. This group can be organized into two event families based on their geometry and style of activation. Furthermore, the two families also show spatial and temporal separations, which permit estimation of the local direction of flow during the circulation tests. Our interpretation suggests that, based on their location and time of activation, the fluid first reached a fracture family located north of the injection well and close to the same depth. Then, this fracture set channeled the fluids, favoring migration in an east-upward direction following their geometrical orientation until reaching the second fracture zone. The geothermal reservoir at Utah FORGE has been described as containing multiple sets of preexisting fracture families with varying orientation, generally not aligned with the current direction of the maximum horizontal stress. Thus, the moment tensor solutions provide important information to identify which fracture families are being stimulated, and significantly, their relationship to interwell flow during Enhanced Geothermal System operations.