Two primary classes of seismic events are typically associated with hydraulic fracturing of unconventional reservoirs. Small microseismic dip- or oblique-slip events are interpreted as a direct indicator of the opening of hydraulic fractures. A second class of events that is sometimes observed are strike-slip events commonly related to fault activation. These strike-slip events are usually very small; however, there are cases where they are large enough that they are detected on surface seismometers. These cases of fault-related seismicity, in the absence of microseismic monitoring, are commonly attributed to basement related faults. Recent cases of relatively low-level induced seismicity in the Anadarko basin have been captured on a number of high-resolution microseismic and regional seismometer arrays. Analysis reveals that these fault related events are only slightly deeper than the treated interval, well above the basement. Activation occurs with direct fluid or proximal fluid communication. Once activated by a stage, activity remains for up to 10 days, compared to hydraulic fracture events where seismicity ends immediately with cessation of pumping. There appears to be a limit on the maximum moment release on any fault, related to the length of the feature that is illuminated. Subsequent activation of the same fault generally does not result in a lower seismicity rate, although the largest events tend to occur on primary activation of the fault. We also note that a second type of strike-slip event is often observed independent of fault activation. These events occur in the completion interval, strike parallel to the hydraulic fracture growth and trend towards pressurized offsetting wellbores. The mechanism of these events is possibly due to a stress rotation and shear on existing hydraulic fractures.
Presentation Date: Wednesday, September 18, 2019
Session Start Time: 8:30 AM
Presentation Start Time: 8:55 AM
Location: 217B
Presentation Type: Oral
