Poroelasticity Contributes to Hydraulic‐Stimulation Induced Pressure Changes. Issue 6 (23rd March 2021) - Dutler, N. O.
Abstract: High‐pressure fluid injections cause transient pore pressure changes over large distances, which may induce seismicity. The zone of influence for such an injection was studied at high spatial resolutions in six decameter‐scaled fluid injection experiments in crystalline rock. Pore pressure time series revealed two distinct responses based on the lag time and magnitude of pressure change, namely, a near‐ and far‐field response. The near‐field response is due to pressure diffusion. In the far‐field, the fast response time and decay of pressure changes are produced by effective stress changes in the anisotropic stress field. Our experiments confirm that fracture fluid pressure perturbations around the injection point are not limited to the near field and can extend beyond the pressurized zone. Plain Language Summary: The far‐field pore pressure response in geological reservoirs due to high pressure fluid injection is not clarified yet. Direct observations of far‐field pore pressure changes were analyzed in the framework of the In‐Situ Stimulation and Circulation project executed at the Grimsel Test Site. The findings show two distinct behavior, one related to pore pressure diffusion in the near‐field of the injection and another one related to poro‐elastic effects. Key Points: Pore pressure time series reveal a near‐field response dominated by pressure diffusion The far‐field is dominated by a quasi‐instantaneous poro‐elastic response due to the static anisotropic stress field Injection data showed pressure changes can extend 3–5 times farther than the pressurized volume because of poroelasticity