Forecasting microseismic cloud shape as a proxy of stimulated rock
volume is essential for the design of an energy extraction system. The
microseismic cloud created during hydraulic stimulation is known
empirically to extend in the maximum principal stress direction.
However, this empirical relationship is often inconsistent with reported
results, and the cloud growth process remains poorly understood. This
study investigates microseismic cloud growth using data obtained from a
hydraulic stimulation project in Basel, Switzerland, and explores its
correlation with measured in-situ stress. We applied principal component
analysis to a time series of microseismic distribution for macroscopic
characterization of microseismic cloud growth in two- and
three-dimensional space. The microseismic cloud in addition to extending
in the direction of maximum principal stress expanded to the direction
of intermediate principal stress too. The orientation of the least
microseismic cloud growth was stable and almost identical to the minimum
principal stress direction. Following the stimulation, the orientation
of microseismic cloud growth was consistent with the in-situ stress
direction. Further, microseismic cloud shape ratios showed good
agreement when compared with in-situ stress magnitude. The permeability
tensor estimated from microseismicity also presented good correlation in
terms of direction and magnitude with microseismic cloud growth. We show
that in-situ stress plays a dominant role by controlling the
permeability of each existing fracture in the reservoir fracture system.
Consequently, microseismic cloud growth can be scaled by in-situ stress
if there is sufficient variation in the existing faults.