Quantification of Poroelastic Effects at the EGS Collab Site

Poroelastic effects are often assumed to be negligible because of the low porosity of EGS reservoir rocks. Recent observations from the EGS Collab site will be presented that suggest that poroelastic effects may be significant even in low porosity formations. The EGS Collab project is a meso-scale (10 meters between injection and production well) project hosted in a phyllite formation at approximately 4850 feet below ground surface. Hydraulic fractures were created to make a connection between the injection and production well, and chilled water was circulated between the two wells nearly continuously for nearly a year at a constant rate. The poster will show that how the injection pressure varied and the fracture reopening pressure, observed during brief interruptions of injection, suggests that poroelastic effects are significant. This has important implications for the closure stress and hence fracture conductivity evolution during long term circulation through EGS reservoirs.