Remote Triggering of Large Events during Hydraulic Fracture Stimulations

摘要

Hydraulic fracture stimulations result in the re-distribution of stress adjacent to the treatment well that in turn may result in the triggering of seismicity. Generally, seismicity only occurs when the triggering source, such as the injection of proppants, acts to drive the pre-existing stress field closer to failure levels of susceptible fractures/faults. If we consider that the observed seismicity is a function of the stress state and its interaction with the fracture network, under some conditions, it might be possible that seismicity may then occur at distances beyond the volume related to or directly influenced by the stimulation. Currently, the extent of seismic influence, including the potential for remote mobilization of pre-existing structures, the potential for ou ut-of-zone fluid communication, and the relative stress and stress transfer conditions leading to large event occurrence (M > 0) are not well understood. In this paper, we investigate the spatial and temporal variations in microseismicity associated with hydraulic fracture treatment of a shale play in North America during which distant larger magnitude events were triggered. These events, in this example, were located up to several hundred metres away from the stimulations, and in some cases in different formations from the reservoir host rock. These datasets, including calculated source parameters such as apparent stress and seismic moment, provide the basis for examining the conditions under which remote structures can be activated and how the distribution of microseismicty can be used to establish the region of stimulation influence. Based on these observations we postulate on the potential of triggering events remotely.