Experimental Reactivation of Shear‐fractured Berea and Boise Sandstones by Brine or Liquid CO2 Injection at Depth. Issue 2 (3rd February 2020)

• Record Type: Journal Article
• Authors: Velcin, Helene; Dautriat, Jeremie; Sarout, Joel; Esteban, Lionel; Godel, Belinda
• Is Part Of: Journal of geophysical research. Volume 125:Issue 2(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-02-03
• Subjects: fault reactivation -- fluid injection -- induced seismicity -- laboratory simulation -- triaxial stress -- microseismic imaging; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2019JB018281
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Injection‐driven reactivation of fractured/faulted reservoirs is a key concern in the design and safe operation of water/CO2 injection projects. Here, a new laboratory testing protocol is devised by which the reactivation conditions are quantified, providing pivotal data for effective risk assessment/management. We simulate a field injection operation in the laboratory on prefaulted Berea and Boise sandstones subjected to stress/pressure conditions prevalent at 2 km depth. The protocol consists of two key stages: (i) drained normal faulting: triaxial shear failure induced by increase of the overburden stress; and (ii) injection‐driven reactivation of the faulted rock by pore pressure increase. Injection is conducted with either brine or liquid CO2 . The data show that at 2 km depth, (i) shear fracturing and subsequent faulting occurs when the differential stress reaches 36–46 MPa for Boise, or 96–98 MPa for Berea, and (ii) subsequent reactivation triggers when the pore fluid over‐pressure reaches 4–5 MPa, regardless of the injected fluid or specific sandstone tested. Spatiotemporal monitoring of the concomitant microseismic activity proves effective in time‐lapse imaging the structural changes leading to the triaxial faulting of the intact rock, or to the reactivation of the prefaulted rock. Microseismic imaging suggests that (i) initial shear faulting results in a single slip surface, consistent with brittle (Berea) or semibrittle (Boise) failure; (ii) upon injection‐induced reactivation at 2 km depth, the preexisting fault ruptures and slips first, before a new and steeper fracture nucleates, progressively propagates, then slips; and (iii) dynamic slip transfer occurs from the preexisting to the newly formed fault. Key Points: Injection‐driven reactivation in two fractured reservoir analogues at 2 km depth in the normal‐faulting regime simulated in the laboratory Microseismic imaging shows that shear faulting leads to a single slip surface, whereas reactivation leads to a steeper secondary fault No significant difference between brine and liquid CO2 injection in Boise and Berea sandstones is observed within the injection time scale