Analysis of Micro-earthquake Data at Cold Lake and its Applications to Reservoir Monitoring

Over four months of continuously recorded microearthquake data acquired at Cold Lake, Canada was analyzed using advanced algorithms for micro-earthquake location and subsurface imaging. Robust determination of the spatial, temporal and magnitude distribution of seismicity is the first step towards understanding the relationship between the stress perturbations caused by the Cyclic Steam Stimulation (CSS) process and seismicity. The acquisition geometry was constrained because the receivers were only located in a single vertical borehole. Despite this constraint, we were successful in improving event locations, which highlight several tight clusters of events. The clusters migrate to shallower depths with successive steam cycles. This shows that repeated steaming causes the deformation to spread to shallower depths, thus increasing the risk for fluid incursion in the overburden shales. Though some of the largest events occur in or below the Clearwater reservoir, we observe very few events in the reservoir itself. The size and distribution of seismicity agree to the first order with predictions from simple geomechanical modeling, but are also probably controlled by lithologic variations.