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AAPG Bulletin

Abstract

(Begin page 587)

AAPG Bulletin, V. 85, No. 4 (April 2001), P. 587-600.

Copyright ©2001. The American Association of Petroleum Geologists. All rights reserved.

Displacement distributions on extensional faults: Implications for Previous HitfaultNext Hit stretch, linkage, and seal

S. A. Stewart1

1Upstream Technology Group, BP, Burnside Road, Farburn Industrial Estate, Dyce, Aberdeen AB21 7PB, United Kingdom; email: [email protected]

AUTHORS

Simon Stewart completed a Ph.D. at Imperial College, London, on the structural geology and paleomagnetism of the Carboniferous thrust belt in north Spain. Since then he has spent eight years at Amerada Hess on various North Sea teams, working mainly on three-dimensional (3-D) seismic interpretation. In 2000 he joined BP as a structural geologist, working on the application of integrated drilling, geomechanical, and seismic data. His special interests include the relationship between mechanostratigraphy and structural style and development of 3-D seismic interpretation work flows for fast, accurate mapping.

ACKNOWLEDGMENTS

This article benefited from reviews by R. Schlische and G. Yielding and comments from J. Cartwright and J. Underhill. I thank T. Wynn for assisting with programming. The mapping shown in Figure 6a is by J. Argent. I thank Veritas DGC for permission to show seismic data. The views expressed here are solely my own and do not necessarily represent those of Amerada Hess Ltd. or BP.

ABSTRACT

Most extensional faults are characterized by displacement distri butions that range from zero at the Previous HitfaultNext Hit tips to a maximum value at some point along the length of the Previous HitfaultNext Hit. Regardless of the pattern of displacement distribution, a geometrical requirement resulting from the displacement variation along the Previous HitfaultNext Hit is that beds must stretch parallel with the strike of the Previous HitfaultNext Hit. It has been suggested that minor faults and fractures evolve perpendicular to the main Previous HitfaultNext Hit to accommodate this stretch. The amount of stretch that this subpopulation of faults must accommodate is quantified here using several alternative displacement profile models. The choice of pro file model is much less significant than the ratio of maximum displacement to Previous HitfaultNext Hit length (Dmax/L). The amount of stretch rapidly increases from about 0.7% at Dmax/L of 0.05 to about 3% at the typical upper limit for Dmax/L of 0.1. These relationships predict tens to hundreds of meters of Previous HitfaultNext Hit-parallel stretch associated with kilometer-scale extensional faults. The size and spatial distribution of stretch accommodation faults should be incorporated in three-dimensional (3-D) Previous HitfaultNext Hit zone models, and there are several implications for Previous HitfaultNext Hit linkage and seal. One possible strain accommodation scenario is that a small number of faults that have displacements significant enough to generate reservoir-juxtaposition leak points could exist. Alternatively, a subseismic Previous HitfaultNext Hit and fracture population could either significantly degrade horizontal permeability parallel with the major Previous HitfaultNext Hit or, if open, constitute a target for high-angle exploitation drilling. The intersections between the stretch accommodation faults and the main Previous HitfaultNext Hit could provide conduits for Previous HitfaultNext Hit valving or low-entry pressure leak points. The most commonly observed candidate stretch accommodation faults occur in Previous HitfaultNext Hit overlap zones in segmented Previous HitfaultNext Hit systems, coincident with maximum displacement gradients on the Previous HitfaultNext Hit planes. In these cases, cutoff stretch accommodation could be an integral factor in Previous HitfaultTop segment linkage.

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