Publication Date:
2006-09-01
Description:
Within any faulted reservoir, there are large numbers of faults that are below the resolution of seismic surveys. Some of these faults are encountered in wells, but most of them remain undetected. Such subseismic faults can significantly influence the flow of hydrocarbons during production. The size distribution of subseismic faults can be predicted by extrapolating the size distribution measured at the seismic scale down to the subseismic scale. However, the positions and orientations of the subseismic faults are more difficult to determine. A method based on mechanical modeling is described here to constrain the positions and orientations of subseismic faults. The large, seismically resolvable faults are brought into a three-dimensional (3-D) numerical mechanical model to determine the stress conditions near these faults at the time of faulting. The stress field is then combined with a Coulomb failure criterion to predict the orientations and densities of the smaller faults. This information is represented on a pair of grids (i.e., a density and strike grid). The grids are then used to condition two-dimensional or 3-D stochastic models of faulting, which use a power-law distribution and/or stochastic growth processes to simulate subseismic faults. Two contrasting stochastic methods are used: (1) a method in which the subseismic faults are placed in the volume as fully grown structures and (2) a method in which the faults are allowed to grow and interact. The Oseberg Sør reservoir, northern North Sea, is used as an example of the application of these methods. Methods for incorporating modeled subseismic faults into the reservoir-flow simulation are also discussed. Laurent received his M.Sc. degree in geology from the University of Montpellier, France, in 1994. He completed his Ph.D. in geology and environmental sciences in 1999 at Stanford University in collaboration with Norsk Hydro. He worked at the French Petroleum Institute in Paris as a research engineer in structural geology for 2 years. Laurent is currently the chief executive officer and principal consultant of IGEOSS. His interests focus on geological structures, geomechanical modeling, three-dimensional restoration, and the development of innovative methods to improve hydrocarbon production in fractured reservoirs. Paul Gillespie is a structural geologist specializing in the detection and prediction of fractures at the Hydro Research Centre. He received his M.Sc. degree in structural geology from Imperial College, London, in 1986 and his Ph.D. from the University of Wales, Cardiff, in 1991. Before moving to Norway, he worked in the Fault Analysis Group at Liverpool University. His interests focus on geological structures, fault mechanics, and fracture population. Jean-Marc obtained his Ph.D. in structural geology from the Pierre et Marie Curie University, Paris (1995). Since 1995, he has been a research engineer at the Institut Français du Pétrole (IFP) Geology-Geochemistry Division, at the head of the IFP Structural Geology Department since the beginning of 2002. Jean-Marc is mainly interested in fracture network characterization and modeling both in terms of geometry and fluid flow. From 1997 to 1999, he has managed several research projects concerning the role of faults on fracturing and fluid flow. Jean-Marc is now in charge of analog modeling and the four-dimensional (4-D) description of fault networks and is involved in advanced fractured reservoir studies, including the stochastic modeling of fracture networks. His main areas of interest are the geological description of fracture networks from outcrop and subsurface data, 4-D analog modeling of fault network, and geomodeling.
Print ISSN:
0149-1423
Electronic ISSN:
1943-2674
Topics:
Geosciences
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