Seismic monitoring results from the first 6 months of CO2 injection at the Aquistore geological storage site, Saskatchewan, Canada

Abstract:

The Aquistore Project, located in SE Saskatchewan, Canada, is a demonstration project for CO₂ storage in a deep saline aquifer. CO₂ captured from a nearby coal-fired power plant is being injected into a brine-filled sandstone formation at 3100-3300 m depth. CO₂ injection commenced in April, 2015, at initial rates of up to 250 tonnes per day. Seismic monitoring methods have been employed to track the subsurface CO₂ plume and to record any injection-induced microseismicity. Active seismic methods utilized include 4D surface seismics using a sparse permanent array, 4D vertical seismic profiles (VSP) with both downhole geophones and a fiber optic distributed acoustic sensor (DAS) system. Pre-injection baseline seismic surveys have established very good repeatability with NRMS values as low as 0.07. 3D finite-difference seismic modelling of fluid flow simulations is used with the repeatability estimates to determine the appropriate timing for the first CO₂ monitor surveys. Time-lapse logging is being conducted on a regular basis to provide in situ measurement of the change in seismic velocity associated with changes in CO₂ saturation. Continuous passive seismic recording has been ongoing since the summer of 2012 to establish background local seismicity prior to the start of CO₂ injection. Passive monitoring is being conducted using two, 2.5 km long, orthogonal linear arrays of surface geophones.with 3-component short-period geophones, 3 broadband surface seismometers, and an array of 3-component short-period geophones in an observation well. No significant injection-related seismicity (M_w > -1) has been detected at the surface during the first 4 months of CO₂ injection. On-going analysis of the downhole passive data will provide further information as to the occurrence of lower magnitude microseismicity (M_w of -1 to -3).