**6. Conclusions**

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 for predicting actual reservoir drainage.

Due to a strong desire for near-real time information by completion engineers, acquisition and service companies have focused predominantly on providing hypocentre locations and moment magnitudes. Microseismic recordings contain, however, a wealth of information beyond event locations, including moment tensors and resonance frequencies. Thus, many pertinent research questions on microseismic acquisition, processing and interpretation remain to be answered before full use of microseismic recordings can be achieved.

Nonetheless, microseismic monitoring has a bright future with long-standing applications such as monitoring of shaft stability in mines and the creation of engineered geothermal systems; more recent applications involve monitoring of hydraulic stimulation of "tight" hydrocarbon reservoirs and steam-injection in heavy-oil fields. Future applications may incorporate surveillance of CO2 storage as well as slurried waste solids disposal through continuous injection.
