The release of microseismic energy is a geomechanical phenomenon that takes place when the failure criterion of any discontinuity in the sub-surface is exceeded. Each microseismic event represents a discrete shear or opening movement at or along such a discontinuity.

Microseismic events can therefore take place along bedding planes, fracture planes, joint planes, fault planes or can be associated within or between man-made structures associated with oilfield sub-surface development. The majority of detectable microseismic events are dominated by shear slip rather than opening modes. The acceleration and deceleration of rock associated with microseismic slip generates seismic waves that propagate through the sub-surface and can be detected with the use of appropriate downhole or surface sensors.

On a basic level, the detection and analysis of these waveforms allows estimation of the event location. More advanced analysis provides information about the nature of the source and the medium through which these seismic waves have travelled on their journey from source to receiver. Such analysis can provide estimates of the orientation and size of the discontinuity, the amount of slip and perhaps most importantly the mechanism by which failure has taken place.

The most common oilfield application for microseismic monitoring technology is that of hydraulic fracture monitoring (HFM). Microseismic monitoring can provide real-time maps of event locations that are used to map to the dimensions of the growing hydraulic fracture. Advanced microseismic source analysis can derive the proportion of shear and opening characteristic of each microseismic event, thereby providing a more informed understanding of the nature of the developing hydraulic fracture.

Although the HFM application, based on downhole wireline tool provision, is the most common use of microseismic technology, it represents only one specific application of this technology. It has recently been shown that large surface monitoring networks are capable of detecting microseismic energy release in the sub-surface (“Multi-network microseismic monitoring of fracturing jobs. Neuquen TGR application”, D. Drapeau & al.). Full field permanent microseismic installations provide the opportunity to monitor any oilfield operations that are likely to cause pressure change, stress change or strength change in the sub-surface. As with many cross-discipline technologies associated with the “digital oilfield”, the use of microseismic technology for full-field monitoring is still in its infancy since it requires the

- parallel development of reliable downhole monitoring devices
- integration of microseismic information with reservoir production and injection data
- integration with geomechanical sub-surface data
- predictable demonstration of the value proposition

At present the value proposition is clear for certain applications such as steam-flood monitoring, well integrity monitoring, frac monitoring and acid stimulation. The nature of production related stress/pressure change has been shown to have value in understanding fault reactivation and compartmentalisation.

In combination with Baker Hughes affiliated companies and divisions: GMI, Gaffney Cline, VSFusion and ProductionQuest, together with CGGVeritas seismic technologies such as SeisMovie, Magnitude is able to deliver turn-key solutions for all forms of reservoir monitoring applications.