Passive Seismic Monitoring of Hydraulic Fracture Stimulations: What Have we Learned from Over a Decade of Monitoring?

English Abstract:

Since the late 1990s with initial passive seismic monitoring projects in the Cotton Valley, East Texas a tremendous evolution in understanding of hydraulic fracture treatments has taken place. Most monitoring efforts have focused on determining event locations for events with M<0. However, based on recent deployments, it is fair to say that stimulations, particularly as related to unconventional reservoir exploitations, can result in observations of seismicity that cover over 6 orders of magnitude from -3 < M < +3. These events generally follow self-similar seismic trends; however, they tend to be smaller stress release events relative to tectonic events. Most observed events are related to failure of pre-existing fractures and are controlled by local stress perturbations as related to the stimulation process. Larger events, up to +M3, are related to the activation of faults in the reservoir or in adjacent formations and have fault lengths ranging up to ~750m length. By increasing the bandwidth of coverage, this is allowing operators to begin developing treatment programs to potentially control the fracture growth and extent. As most unconventional reservoirs are typically located at depths >2km, our observations suggest that hydraulic fracturing will have minimal potential impact on near-surface activities or aquifers. Overall, the extensive databases collected over the past decade have been instrumental in understanding hydraulic fracture growth thereby allowing for better constraint of geomechanical and reservoir models used in stimulation/well design.