Geomechanical impacts on flow in fractured reservoirs

Abstract

AbstractFlow responses in fractured reservoirs are difficult to predict. Apparent success in predicting flow has been achieved by developing simple rules of thumb based on (i) alterations of effective stress associated with pore pressure changes or (ii) concepts about fracture aperture alterations due to stress changes. Here it is argued that the assumptions underlying these explanations of flow are flawed, as they are based on ideas about stress that are physically wrong. It may be that these simple ideas can be fitted to some observations, but their use in this fashion is highly risky. The role of geomechanics in fractured reservoirs is more complex than suggested by the simple rules of thumb, as illustrated by numerical simulations that demonstrate the occurrence of strong non-linear interactions between the fluids, the geomechanics of blocky systems, and thermal changes. The resulting movements within fractured rock masses can cause major alterations of the upscaled flow properties. Flow performance discrepancies that are often associated with the operation of fractured reservoirs can, and often should, be seen as a consequence of motions occurring within the fractured rock mass. The explanations developed here are phenomenologically correct, and are more holistic than existing simple rules of thumb, improving the reliability of predictions.