Injection into the subsurface is carried out by industry for a variety of reasons, for example, storing wastewater, enhanced oil recovery, and hydraulic fracture stimulation. By increasing subsurface pressures, injection can trigger felt seismicity (i.e., sufficient magnitude to be felt at the surface) on pre‐existing faults. As the number of cases of felt seismicity associated with hydraulic fracturing (HF) has increased, strategies for mitigating induced seismicity are required. However, most hydraulic stimulation activities do not induce felt seismicity. Therefore, a mitigation strategy is required that is capable of differentiating the normal case from abnormal cases that trigger larger events. In this article, we test the ability of statistical methods to estimate the largest event size during stimulation, applying these approaches to two datasets collected during hydraulic stimulation in the Horn River Shale, British Columbia, where HF was observed to reactivate faults. We apply these methods in a prospective manner, using the microseismicity recorded during the early phases of a stimulation stage to make forecasts about what will happen as the stage continues. We do so to put ourselves in the shoes of an operator or regulator, where decisions must be taken based on data as it is acquired, rather than a post hoc analysis once a stimulation stage has been completed. We find that the proposed methods can provide a reasonable forecast of the largest event to occur during each stage. This means that these methods can be used as the basis of a mitigation strategy for induced seismicity.

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