| Title | Fracture Caging to Control Induced Seismicity with Inspiration from the EGS Collab Project |
|---|---|
| Authors | Luke FRASH, Jesse HAMPTON, Marte GUTIERREZ, EGS COLLAB Team |
| Year | 2020 |
| Conference | Stanford Geothermal Workshop |
| Keywords | Multiple Wells, Reservoir Development, Earthquake Prediction, Fracture Network |
| Abstract | In 2018, we introduced the concept of ‘fracture caging’ at the Stanford Geothermal Workshop. The concept involves drilling intelligent patterns of production wells around injection wells to improve EGS reservoir efficiency and to limit out-of-zone fracture growth. Experiments and modelling that validated this concept were inspired during the design phase of the eight-well EGS Collab Experiment 1 site at the Sanford Underground Research Facility (SURF). Recently, we discovered that fracture caging could also offer a means to control earthquakes that would otherwise be caused by injection induced seismicity. Limited seismicity in fracture caged systems is evidenced by field and laboratory observations of reduced seismic event magnitudes and reduced rates of seismic event occurrence in multi-well systems. Field examples of this effect from Hijiori, Pohang, and numerous injection dominated sites as well as laboratory examples with single and multi-well large block hydraulic stimulation and fluid circulation studies are presented. In this paper, we propose a mechanism linking fracture caging and reduced seismic risk and we elaborate on the potential of this mechanism to directly control the risk of earthquakes generated by EGS sites. We also discuss our expected limitations for this new method that include complications arising from natural rock complexity and the cost of drilling additional wells. When scaled to large arrays of wells, this method appears to become increasingly feasible. While this fracture caging concept is relatively new, it does share similarities to proven reservoir management methods and it could be that, with sufficiently convincing validation, ‘fracture caging’ will address the need to prevent the damaging induced seismic events that could otherwise be generated from geothermal energy projects. |