Microseismic Magnitudes and b-Values for Delineating Hydraulic Fracturing and Depletion

In 2014, Hess Corporation collected microseismic and hydraulic-fracturing data in a Bakken field trial near an existing oil well in the Williston Basin of North Dakota. In addition to monitoring the microseismic activity of the newly drilled offset-well completions, the field test delineated the depletion surrounding the original well by slowly repressurizing it. This repressurization induced shear-slip events, which preferentially delineated the depleted zone of the producer well, a process we call microseismic depletion delineation (MDD). By comparing the magnitudes of the depletion-related events to those that accompanied the new offset completions, we observe that higher magnitude microseismic events occur within the depleted interval. This paper offers an explanation for why higher magnitudes appear in the depleted zone and suggests that measuring magnitude statistics in the form of b-values can provide a qualitative assessment of the relative contribution of oil from completions along a wellbore.