Distributed Acoustic Sensing Strain Signatures as an Indicator of Fracture Connectivity in Enhanced Geothermal Systems

Abstract

Stimulated fracture connectivity between injector and producer is a critical prerequisite for efficient EGS thermal recovery. Some stimulated fractures may be incomplete, approaching but not intersecting the production well. These “near-miss” fractures can be addressed in future stimulation stages or re-stimulated to complete the connection. We propose the use of fiber optic distributed acoustic sensing (DAS) as a method by which near-miss stimulated fractures may be identified and distinguished from hydraulically connected fractures. The low-frequency sub-nanostrain signatures of both complete and near-miss fractures in DAS data are simulated in this study using a hydrogeomechanical discrete fracture network model. The spatial distribution of strain was found to be indicative. However, this indicator must be evaluated in the context of DAS gauge length and spatial sampling. These simulations are a precursor to tests to be conducted at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE) in 2023.