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Abstract
Porter, M. L., A. R. G. Sprague, M. D. Sullivan, D. C. Jennette, R. T. Beaubouef, T. R. Garfield, C. Rossen, D. K. Sickafoose, G. N. Jensen, S. J. Friedmann, and D. C. Mohrig,
DOI:10.1306/1215880M883273
2006. The American Association of Petroleum Geologists. All rights reserved.
Stratigraphic Organization and Predictability of Mixed Coarse- and Fine-grained Lithofacies Successions in a Lower Miocene Deep-water Slope-channel System, Angola Block 15
M. L. Porter,1 A. R. G. Sprague,2 M. D. Sullivan,3 D. C. Jennette,4 R. T. Beaubouef,5 T. R. Garfield,6 C. Rossen,7 D. K. Sickafoose,8 G. N. Jensen,9 S. J. Friedmann,10 D. C. Mohrig11
1ExxonMobil Production Company, Houston, Texas, U.S.A.
2ExxonMobil Upstream Research Company, Houston, Texas, U.S.A.
3Chevron Energy Technology Company, Houston, Texas, U.S.A.
4Apache Oil, Houston, Texas, U.S.A.
5ExxonMobil Exploration Company, Houston, Texas, U.S.A.
6ExxonMobil Production Company, Houston, Texas, U.S.A.
7ExxonMobil Development Company, Houston, Texas, U.S.A.
8ExxonMobil Exploration Company, Houston, Texas, U.S.A.
9ExxonMobil Production Company, Houston, Texas, U.S.A.
10Lawrence Livermore Laboratory, Livermore, California, U.S.A.
11Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Boston, Massachusetts, U.S.A.
ACKNOWLEDGMENTS
The authors thank ExxonMobil, together with Angola Block 15 coventurers British Petroleum, Statoil, and ENI for permission to publish our work on this lower Miocene deep-water system. We also express our gratitude to Sociedade Nacional de Combustiveis de Angola (Sonangol) for the opportunity to study and develop these world-class reservoirs. Our work includes substantial contributions from numerous prospect and development geoscientists in the Exploration and Development companies of ExxonMobil. We thank John Ardill, Dana Butters, Tim Fahrer, E-Chien Foo, Matt Grove, Randy Kissling, Dave Mason, Lisa McBee, Jose Sequeira, Mark Rosin, and Bill Tate for their insight to the geology of Bur1 slope-channel system. Reviews by Laurence Droz (University of Brest) and Carlos Pirmez (Shell Oil) greatly improved the manuscript. The views expressed in this study are those of the authors and ExxonMobil and do not necessarily reflect those of the concessionaire or the Block 15 contractor group.
ABSTRACT
Regional seismic mapping identified lower and middle Miocene slope channels as significant exploration targets for Angola Block 15. Seventeen exploration wells, followed by four appraisal wells, established these slope-channel complexes as a world-class development opportunity. ExxonMobil's current development activity targets stacked turbidite-dominated reservoirs in long-reach, high-angle wellbores tied back to tension leg platform (TLP) and close-moored floating production, storage, and offshore loading facilities.
One of the major development targets in Block 15 is the Burdigalian-aged (Bur1) slope-channel reservoirs. The Bur1 slope-channel system was one of many lower Miocene sediment fairways that provided a mechanism for the delivery of coarse-grained turbidites and mixed muddy and sandy debrites into the Lower Congo basin. This slope-channel system traverses across the block in an east–west direction and can be continuously mapped on adjacent seismic data sets across a 30–40-km (18–25-mi) reach. Three conventional cores and 28 well penetrations calibrate updip to downdip changes in lithofacies type and channel architecture. Map patterns of the Bur1 slope-channel system show distinctive changes in sinuosity, channel confinement, and degree of amalgamation broadly related to concurrent growth of salt-related structures. Channel-complex confinement is more pronounced, and vertical amalgamation is better developed in segments that cross
structural
highs. The Bur1 channel system shows weaker lateral amalgamation, greater sinuosity, and less erosional confinement in
structural
lows.
The episodic fill of the Bur1 slope-channel system can be better understood by a hierarchical arrangement of unconformity-bounded stratal units. Within these unconformity-bounded channel sets, nested channels form composite channel complexes that show distinctive trends in lithofacies type and vertical facies succession. Compared to other offshore Angola slope-channel systems, this Bur1 system is noteworthy because of the relatively coarse granule to cobble grain sizes encountered. Well logs and high-resolution seismic data calibrated to conventional cores show that the lower parts of the channel complexes are dominated by sandy-muddy debrites, slumps, and injected sandstones. These facies are typically overlain by coarse-grained, gravelly, and well-amalgamated sandy turbidites. The overlying facies succession is more variable, but commonly consists of interbedded sandy and muddy turbidites, injected sandstones, and a range of both muddy and sandy debrites.
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