Characterizing Spatiotemporal Deformation in the Reservoir as Related to Hydraulic Fracture Stimulations

Abstract

Hydraulic fracture stimulations result in the occurrence of microseismic events that individually correspond to shear or shear-tensile slip of a discrete surface. The acoustic signals generated by these events provide details about the rupturing and fracturing processes, their failure mechanisms and the local stress-strain conditions leading to failure. The fracture volume, also referred to as the source volume, suggests that the altered rock in the presence of these fractures can be described by the acoustic signals recorded by near-by sensors. By considering the spatiotemporal inter-relationships between events, the collective behaviour can then be used to characterize, map and study the dynamic rock behaviour of a reservoir's response to injections during stimulations. By using a series of identified microseimic source characteristics for different spatial event clusters, such as seismic moment, seismic energy and apparent stress release, and their inter-relationships, we can examine the rate of diffusion associated with event occurrences in the reservoir (Diffusion Index), the susceptibility of a rock mass to fracturing, or the ease in which the reservoir deforms in response to fluid injection (Plasticity Index). In applying these concepts we can use microseimicity to identify growth away from injection zones based on rock property variations that can more closely be tied into potential production volumes. Through the examples provided, we were able to highlight stimulated regions of increased deformation (high Plasticity Index) that correlated to zones of increased production volumes and flow as identified through PLT data. These zones were further described by the behaviour of Diffusion Index, which showed slower, more stable development of fracturing in these volumes. By considering the apparent stress release, regions of high apparent stress and low Plasticity Index were suggestive of regions of stress activation of fractures whereas high apparent stress and Plasticity Index volumes were easily deformed under the influence of injection fluids. In using these data, the confined zones of increased Plasticity Index appear to be a good proxy for characterizing the resulting rock mass behaviour under different injection and well positioning and staging schemes.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016