Microseismic monitoring is increasingly used to describe the extent of hydraulic stimulations in unconventional reservoirs. The key to this reconstruction is the realization that a singular microseismic event is the result of a rupture of a crack, likely associated with pre-existing lineaments in the subsurface, where the final areal extent and failure of the rupture is controlled by the frictional characteristics of this surface. Building on this concept, we discuss how microseismicity does not occur in isolation, but through clustering properties of the microseismicity that allows us to characterize the deformation in the reservoir, and further define volumes within the reservoir that are more consistent with interpretations of fluid vs stress activation. We describe the collective behavior through a series of “dynamic parameters” that describe the ability for the reservoir to deform with the seismicity and transfer stress.
We connect these concepts of fluid-driven vs stress-triggered seismicity to volumes in the reservoir of different percolation potentials. Fluid-driven processes are of primary importance to tying the microseismicity to productive volume, but we suggest that the stress-induced processes may also play a significant role in identifying poorly- or well-connected crack networks and hence the stimulated volumes within the reservoir. As such, we can resolve the likely volumes of primary (initial) and secondary (longer-term) production through these clustering processes and ensuring the behaviors determined are consistent with more of a fluid-induced vs stress-triggered behavior. This ranking of volumes in terms of productivity is analogous to work done in predicting variations in enhanced permeability in different engineering workflows, with the added benefit of being able to show variability along the well. As such, we suggest that coupling the dynamic parameter response to estimating and ranking the geometries of volumes of different productivity provides a rigorous methodology to tie microseismicity to stimulated reservoir volume, allowing for credible predictions of accessible reserves to be made over a short timescale.
Check out our full article published by Unconventional Resources Technology Conference (URTEC-2697672-MS) or contact us to get a copy.