SHALE SYMPOSIUM
RUPTURE DYNAMICS AND SOURCE SCALING RELATIONS OF MICRO-SEISMIC
HYDRAULIC FRACTURES IN SHALE RESERVOIRS
*Gisela Viegas, Ted Urbancic, and Adam Baig
ESG Solutions
(*Corresponding author: gisela.fernandes@esgsolutions.com)
ABSTRACT
To characterize the failure process and source scaling relations of micro-seismic events induced during
a hydraulic fracturing shale completion program in NE British Columbia, Canada, we estimate static
and dynamic source parameters, such as dynamic and static stress drop, radiated energy, seismic
efficiency, moment tensor, fault plane and rupture velocity.
The relationships between the different source parameters combined with the in-situ stress field and the
source rock properties information provide valuable information on the rupture process giving insights
into the generation and development process of the discrete fracture network, the resisting frictional
stress of the rock and the influence of pore pressure perturbations under the local stress field, the
partition of energy into the different physical processes during failure and characteristic rupture
behaviors.
The stress released by a seismic event is directly connected with the state of stress in the source area,
the rupturing mechanism and the physical properties of the source rock. Seismic events occurring in
the same stress conditions and host rock tend to behave self-similarly, that is, tend to reproduce
themselves in different time and space scales. Non-similar behavior is often observed for events with
tensile mechanisms in highly fractured zones, and is related to stress interaction with pre-existing
fractures under confinement and inherent fracturing complexity. The injection of fluids also alters the
self-similar behavior of seismic events as it alters the local stress field and reduces frictional resistance
in the fracture plane, thus generating an altered seismic signature.
The micro-seismic events analyzed in this study were recorded using three multi-sensor arrays of high
frequency geophones temporarily placed close to treatment area at reservoir depth. From the total
number of micro-seismic events detected and located, about 30,000 have good signal quality and focal
coverage that permits a more detailed source analysis. Initial analysis of the results of this study
reveals interesting correlations between rupture failures and other parameters. In average the microseismic events have low radiated energy, low dynamic stress and low seismic efficiency, consistent
with the obtained slow rupture velocities. Events fail in overshoot mode (slip weakening failure
model), with fluids lubricating faults and decreasing friction resistance. Events occurring in deeper
formations tend to have faster rupture velocities and are more efficient in radiating energy. Variations
in rupture velocity tend to correlate with variation in depth, fault azimuth and elapsed time, reflecting a
dominance of the local stress field other factors. Several regions with different characteristic failure
modes are identifiable based on coherent stress drop, seismic efficiency, rupture velocities and fracture
orientation.
Further identification of spatial and temporal distribution of families of events with similar
characteristic rupture behaviors, based on either rock formation, depth, source type, fracture plane
orientation, stress drop, pad or proppant stage, may be used as a proxy for specific fracture network
development and hydrocarbon production. This information can be used to determine reservoir
geophysical properties, constrain reservoir geo-mechanical models with measured physical parameters,
classify dynamic rupture processes for fracture models and improve fracture treatment designs.
KEYWORDS
Microseismic, Rupture Dynamics, Source Scaling, Hydraulic Fracturing, Hydrocarbon, Shale