Advances in the Study of Fractured Reservoirs

Naturally fractured reservoirs constitute a substantial percentage of remaining hydrocarbon resources; they create exploration targets in otherwise impermeable rocks, including under-explored crystalline basement; and they can be used as geological stores for anthropogenic carbon dioxide. Their complex behaviour during production has traditionally proved difficult to predict, causing a large degree of uncertainty in reservoir development. The applied study of naturally fractured reservoirs seeks to constrain this uncertainty by developing new understanding, and is necessarily a broad, integrated, interdisciplinary topic. This book addresses some of the challenges and advances in knowledge, approaches, concepts, and methods used to characterize the interplay of rock matrix and fracture networks, relevant to fluid flow and hydrocarbon recovery. Topics include: describing, characterizing and identifying controls on fracture networks from outcrops, cores, geophysical data, digital and numerical models; geomechanical influences on reservoir behaviour; numerical modelling and simulation of fluid flow; and case studies of the exploration and development of carbonate, siliciclastic and metamorphic naturally fractured reservoirs.
Geomechanical impacts on flow in fractured reservoirs
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Published:January 01, 2014
Abstract
Flow 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.