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AAPG Bulletin

Abstract

AAPG Bulletin, V. 93, No. 6 (June 2009), P. 763-794.

Copyright copy2009. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/02230908094

Four-dimensional analysis of the Sembo relay system, offshore Angola: Implications for Previous HitfaultNext Hit growth in salt-detached settings

David M. Dutton,1 Bruce D. Trudgill2

1Nexen Petroleum UK Ltd., Charter Place, Vine Street, Uxbridge, Middlesex UB8 1JG, United Kingdom; [email protected]
2Department of Geology and Geological Engineering, Colorado School of Mines, Golden, Colorado, 80401-1877; [email protected]

ABSTRACT

Subsurface mapping of several relay ramps from a raft-related Previous HitfaultNext Hit array in the lower Congo Basin, offshore Angola, reveals a full spectrum of Previous HitfaultNext Hit linkage styles. A comprehensive three-dimensional geometric and kinematic appraisal of a more complex relay system within the Previous HitfaultNext Hit array, the Sembo relay system (SRS) highlights differences with current structural models of relay ramp genesis, evolution, and breaching. The SRS is a rearward (upper ramp) breached relay system with a maximum Previous HitfaultNext Hit overlap and spacing of 9500 and 3600 m (~31,000 and 11,800 ft), respectively. This system is characterized by a structural geometry that becomes increasingly complex with depth as the relay system is gradually assimilated into the structural architecture of a separate and structurally deeper Previous HitfaultNext Hit system.

A detailed kinematic appraisal of the SRS indicates that the throw patterns on the frontal and rearward segments are intrinsically different. Throw backstripping reveals different initiation ages for the rearward and frontal segments of about 5.5 and 2.5 Ma, respectively. Mutual overlap is estimated to first occur about 2.5 Ma at the 5.0 Ma structural level, with Previous HitfaultNext Hit linkage and ramp breaching occurring subsequently.

The SRS therefore represents a complex amalgamation of faults that have each developed independently at different times. The genesis and evolution of the SRS have been governed through time by both salt withdrawal and associated Previous HitfaultTop detachment histories, in conjunction with increased Congo Fan progradation and sedimentation rates and phases of tectonic tilting of the underlying salt detachment surface.

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