Downhole Microseismic Monitoring of Injection Stimulations at the Utah FORGE EGS Site

Abstract

ABSTRACT: Downhole microseismic monitoring provides the best means of detecting, mapping and characterizing the fracture systems developed during the creation and evolution of Enhanced Geothermal System (EGS) reservoirs. EGS development requires at least two wells, one for injection and the second for production. During the initial stimulation of well 16A(78)-32, the injection well at the Utah Frontier Observatory for Research in Geothermal Energy, an array of three downhole, high-temperature, eight-level digital receiver strings will be deployed to monitor the fracture system. The well has a true vertical depth of 8540 ft, a measured depth of 10,987 ft, and a maximum temperature of 220°C. Below 7260 ft, the well plunges 25° through the granite basement rock. Three zones will be stimulated near the toe of the well. The configuration of the three monitor wells and the receiver depth placements are designed to resolve the isolation or the possible interference of the stimulated volumes and guide the placement of the production well. After the initial stimulations, the multilevel strings will be replaced with dual-level strings for long-term monitoring. 1. INTRODUCTION The Utah Frontier Observatory for Research in Geothermal Energy (FORGE) project is a test site for demonstrating technologies for Engineered Geothermal Systems (EGS) (Moore et al., 2020). EGS involves the creation of sustainable rock permeability to extract heat for long periods of time. At Utah FORGE, hydraulic stimulation of favorably oriented fractures will be conducted to form the reservoir. Seismicity induced by these stimulations must be monitored to map the EGS reservoir growth and to mitigate possible seismic hazards (Majer et al., 2016). An overview of the guiding risk studies, as well as the history of seismicity at the site and the planning and network deployed for monitoring potential seismic hazards is presented in Pankow et al. (2017); Pankow et al. (2019a); and Pankow et al. (2019b).