AAPG ACE 2018

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Investigating the Complexity of Reservoir Response to Hydraulic Fracturing Through the Lens of Microseismic Collective Behaviour Characterization

Abstract

During hydraulic Fracturing, high pressure injection of fluid and proppant generates stress gradients within a reservoir. The rockmass responds to this change by means of energy, momentum and mass transport to reduce and transfer stresses. Microseismicity is seen as a dissipative process that radiates seismic waves which contains information about the insitu deformation. Through microseismic monitoring, we quantify the changes in the seismic strain and stress regime and rheological properties of the rockmass by considering the aggregate behavior as captured through the use of cluster-based microseismic parameters (dynamic parameters) consisting of Plasticity Index (PI), Diffusion Index (DI), and Stress Index (SI). These parameters are computed using the source characteristics (seismic energy release, stress release, seismic moment) and the inter-event times and distances between events within each cluster.

Through a case study in the Midland Basin, we demonstrate how dynamic parameters characterize a complex reservoir response to hydraulically-stimulated stacked wells where the completion of the investigated stages on one well (A-well) proceed the treatment of the second well (B-well). These two stacked wells target two different siliciclastic formations within 400 ft, separated by a carbonate formation that acts as a hydraulic fracture barrier. Dynamic parameter characterization indicates that the A-well stages generate high anelastic deformation (PI) associated with fluid-driven deformation around the injection interval at early stages of completion where stress is more gradually released through a series of relatively low stress events in a spatially contained target zone (Low SI and DI). The stress-triggered seismicity plays a role for the later event-clusters for these stages. In contrast with this observation, the B-well stages, which are completed after the A-well stages, demonstrate low deformation (Low PI) in the highly stressed rockmass (high SI) where the energy release is more episodic. As the pore pressure increases and stress builds up around the B-well, the seismicity encounters a quick migration to the readily deformed zone around the A-Well and surrounding depleted zones. Therefore the later event-clusters of B-well stages are identified with ease of deformation and diffusivity (high PI and DI). We believe that this complex response for the B-well stages is due to stress shadowing and can be fully captured by dynamic parameters analysis.