**Acknowledgements**

Continuum-based approaches such as finite-element methods may be required for coupled fluid-flow and geomechanical simulation (Dean et al., 2003; Minkoff et al., 2003; Angus et al., 2010). On the other hand, particle-based methods are highly appropriate to modelling crack propagation and brittle failure. Although this is feasible with continuum-based approaches it leads to highly expensive computations. Angus et al. (2010), for instance, circumvent the requirement for modelling fracture propagation by assuming that the differential effective stress tensor at the local point of failure is a first-order approxima‐ tion to the local failure mechanism (Zoback and Zoback, 1980). For failure in intact rock this is likely a reasonable assumption, but not for failure along pre-existing weaknesses

Ultimately physical modelling in the laboratory is required to confirm our inferences from the study of analogues and numerical simulations, thereby completing the circle between fluidinduced rock failure, the occurrence of microseismicity and underlying geomechanical deformation. Many authors have studied the links between microseismic event locations and fracture growth in both triaxial compression and hydraulic fracturing tests (Solberg et al., 1980; Sondergeld and Estey, 1981; Kranz et al., 1990; Lockner et al., 1991; Lockner, 1993; Chitrala et al., 2010). Most of these studies were successful in determining the event hypocenters; yet few provided reliable full moment tensor solutions. The latter are essential for better under‐

The analogues are very useful for building a first understanding on what to expect when injecting fluids and/or proppants into the rock matrix (Figures 6 and 7) but the combina‐ tion of numerical simulations and their verification using physical experiments in the laboratory will help to bridge the gap between geophysical data analysis and engineer‐ ing applications of microseismic data by providing a framework for advanced interpreta‐ tion strategies, thereby facilitating completion of the the circle between acquisition,

The recent surge in development of unconventional resources such as shale-gas and heavy-oil plays has created renewed interest in microseismic monitoring. Pore pressure and stress changes during fluid and/or proppant injection lead to an expanding cloud of microseismic events, due to brittle failure in intact rock and additional slip/shearing in naturally fractured rock. The microseismic cloud represents thus a volumetric map of the extent of induced fracture shearing and opening; yet integration of event locations with moment tensors, other geophysical observations and geomechanical constraints is required to determine ultimately the size of the interconnected fracture network, thereby excluding isolated fracturing/shearing, since only the former contributes to the enhanced effective porosity and permeability, required

(Gephart and Forsyth, 1984).

458 Effective and Sustainable Hydraulic Fracturing

standing the actual rock failure mechanisms.

processing and interpretation.

for predicting actual reservoir drainage.

**6. Conclusions**

**5.6. Physical modelling**

The first two authors would like to thank the sponsors of the Microseismic Industry Consor‐ tium for financial support. Arc Resources, Nanometrics and ESG Solutions are particularly thanked for their support of the field project. All authors would like to thank their collabora‐ tors, students and postdocs whose work has contributed tremendously to this paper.
