What to Expect
A series of in-situ injection experiments at 1480 m depth at the Sanford Underground Research Facility in Lead, SD were performed for the EGS Collab project. In a heavily instrumented testbed consisting of eight boreholes, the formation of hydraulic fractures in a metamorphic rock mass is monitored. Here we use passive seismic monitoring, the SIMFIP in-situ displacement sensor and fiber optic sensing to closely track the formation of a hydraulic fracture. During the pressurization stage, and before the onset of hydraulic fracturing, we observed a single shear slip event. The injection pressure at the time of shearing was 13.4 MPa, which is substantially below the minimal principal stress of about 21 MPa. Using the SIMFIP in-situ displacement probe, we were able to record all phases of the shear deformation that could previously only inferred using indirect methods: preslip, coseismic slip and afterslip. Microseismic monitoring of a series of stimulation tests reveals a complex network of multiple hydraulic fracture strands and reactivated shear fractures. The poroelastic response of the artificial reservoir is further illuminated through strain sensing through DAS.
Martin Schoenball is a Research Scientist in the Energy Geosciences Division at LBNL. He obtained his PhD from Karlsruhe Institute of Technology. He continued his research as a joint postdoctoral fellow at Temple University and the U.S. Geological Survey, and as a Feodor-Lynen postdoctoral fellow at Stanford University. He joined Berkeley Lab in 2018. His research is focused on induced seismicity from hydrothermal and enhanced geothermal systems, from hydrocarbon extraction or deep waste water disposal. He uses data from seismic observations and borehole monitoring to study the elastic, poroelastic and inelastic changes of the tectonic stress field due to forced fluid flow and seismic and aseismic deformations in reservoirs. Further interests are on the tectonic stress field, borehole stability and the time-dependent behaviors in rock mechanics from the laboratory to the fault zone scale.