Correlating the Distribution of Microseismic Events with the Stress State for Multi-Stage Stimulations

The aim of microseismic data interpretation is to enable reliable production predictions to be made using reservoir models that contain geological structure extracted from microseismic event clouds, and to enable real-time operational decisions that maximize the effectiveness of hydraulic fracturing. This paper moves towards the latter goal. Previously Bradford (2011) showed that the dynamic behaviour of a system comprising a single hydraulic fracture and neighbouring pre-existing faults can be modeled, using data from Cotton Valley. Specifically, the modeled spatio-temporal pattern of plastic shear deformation on the pre-existing faults matched the sequence and style of microseismic events. This paper extends this technique so that it is applicable to systems comprising tens of hydraulic fractures and multiple pre-existing faults. Data from a multi-well, multi-stage stimulation in the Fayetteville Shale, where there was a deep monitoring well, illustrate the technique. It is shown that the pattern of observed microseismicity is strongly influenced by the induced stress state. Specifically, deformation on pre-existing faults in the vicinity of the hydraulic fractures generates regions of varying compression. The zones of observed microseismicity and those regions of lower compression at, or near, failure, correlate well.