Clare Slightam, 2014. "Characterizing seismic-scale faults pre- and post-drilling; Lewisian Basement, West of Shetlands, UK", Advances in the Study of Fractured Reservoirs, G. H. Spence, J. Redfern, R. Aguilera, T. G. Bevan, J. W. Cosgrove, G. D. Couples, J.-M. Daniel
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Three exploration wells drilled in the West of Shetlands targeted crystalline Lewisian Basement as the primary reservoir. The objective of these wells was to demonstrate the presence of movable oil in basement and the viability of fault zones within the Lewisian Basement as an exploration target. Lewisian Basement reservoir properties were defined pre-drill through a combination of fieldwork, offset well data, global basement analogues and detailed 3D seismic interpretation. Dip, azimuth and similarity attributes were analysed within the 3D seismic volume in order to delineate the fault network, complimenting manual fault interpretation. Once the fault network had been defined, two fault zones were chosen as a reservoir target for an inclined basement well, based on their length and location within the reservoir.
After drilling over a kilometre of basement across three wells, significant understanding has been gained of the basement reservoir. The comprehensive suites of log data obtained from the wells have allowed some leading edge techniques to be used to bridge the gap between wellbore data and seismic data, with fault zones identified from log data tying to fault zones that had been interpreted using seismic data. The well results have been used to feed back into the predicted fault model to increase the number of mapped faults and to constrain rock properties including lithology and fracture frequency. This paper summarizes the above process and provides specific details regarding the seismic characterization of the fault network.
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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.