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Abstract

Krueger, Scot W., and Neil T. Grant, 2011, The growth history of toe thrusts of the Niger Delta and the role of pore pressure, in K. McClay, J. Shaw, and J. Suppe, eds., Thrust fault-related folding: AAPG Memoir 94, p. 357390.

DOI:10.1306/13251345M943435

Copyright copy2011 by The American Association of Petroleum Geologists.

The Growth History of Toe Thrusts of the Niger Delta and the Role of Pore Pressure

Scot W. Krueger,1 Neil T. Grant2

1BP America Inc., Houston, Texas, U.S.A.
2ConocoPhillips (United Kingdom) Ltd., Aberdeen, United Kingdom

ACKNOWLEDGMENTS

We would like to thank ConocoPhillips and its partners for their support of regional studies of the Niger Delta and for the permission to publish this work. No regionally based analysis is possible without the previous efforts of countless past interpreters from the Nigeria Exploration Team, and their efforts are gratefully acknowledged. The manuscript benefited greatly from thorough reviews by John Suppe, Ken McClay, and Juergen Adam. Technical support from Ron Martinussen is greatly appreciated.

ABSTRACT

The evolution of thrust structures in the toe-thrust belt of the Niger Delta has been analyzed and reveals a common growth history. Once initiated, structures propagate rapidly along strike with minimal slip. Subsequently, the propagation slows or ceases, and slip accumulation begins to dominate. In the waning stage, deformation retreats toward structural culminations. The pattern of slip evolution across the deep-water thrust belt indicates that neighboring structures are active simultaneously. A structural restoration across the western Niger Delta suggests that a series of detachment advances in the late Miocene initiated when the Akata shale detachment horizon was buried to a depth of around 4 km (2.5 mi) below mud line. These produced a deep-water fold and thrust belt accommodating more than 12 km (7 mi) of shortening. Deformation combined with compaction disequilibrium may have helped produce elevated pore pressures approaching the fracture gradient in the detachment zone. Once the thrust structures began to attain structural height, pore-pressure transfer developed in interbedded sands and silts within the long backlimb of the fault bend folds. This process may have influenced the behavior of the fault zones. A simple model of pore-pressure evolution within the growing structures indicates that pressure transfer can help explain the localization of out-of-sequence thrust growth and might facilitate the focusing of slip toward the central high-relief parts of thrust structures.

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