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Abstract

AAPG Bulletin, V. 88, No. 10 (October 2004), P. 1357-1367.

Copyright copy2004. The American Association of Petroleum Geologists. All rights reserved.

A simple method of determining sand/shale ratios from seismic analysis of growth faults: An example from upper Oligocene to lower Miocene Niger Delta deposits

S. Pochat,1 S. Castelltort,2 J. Van Den Driessche,3 K. Besnard,4 C. Gumiaux5

1Geacuteosciences Rennes, UMR 6118, Universiteacute de Rennes 1, Av. du Geacuteneacuteral Leclerc, Campus de Beaulieu, 35042 Rennes Cedex, France
2Geacuteosciences Rennes, UMR 6118, Universiteacute de Rennes 1, Av. du Geacuteneacuteral Leclerc, Campus de Beaulieu, 35042 Rennes Cedex, France; Department of Earth Sciences, Eingeidnoumlssische Technische Hochschule-Zentrum, Sonneggstrasse 5, CH-8092 Zuumlrich, Switzerland
3Geacuteosciences Rennes, UMR 6118, Universiteacute de Rennes 1, Av. du Geacuteneacuteral Leclerc, Campus de Beaulieu, 35042 Rennes Cedex, France;
[email protected]
4Geacuteosciences Rennes, UMR 6118, Universiteacute de Rennes 1, Av. du Geacuteneacuteral Leclerc, Campus de Beaulieu, 35042 Rennes Cedex, France
5Geacuteosciences Rennes, UMR 6118, Universiteacute de Rennes 1, Av. du Geacuteneacuteral Leclerc, Campus de Beaulieu, 35042 Rennes Cedex, France

AUTHORS

Steacutephane Pochat completed his Ph.D. in sedimentology and structural geology in June 2003 at Rennes University. He addressed the kinematics of growth faults with examples in deep-water turbiditic environments and their influences on sedimentary processes and made paleoclimatic reconstructions based on lacustrine sedimentology of Permian lakes. He is currently doing postdoctoral studies in the Laboratoire Reacutegional des Ponts et Chausseacutees Institute (Lyon, France) on risks assessment.

Seacutebastien Castelltort completed his Ph.D. in June 2003 at Rennes University. He worked on the origin of high-frequency terrigenous stratigraphic cycles, their relationships with growth folds and faults, and the numerical modeling of fluvial systems. He is now doing postdoctoral studies in the Earth Surface Processes Group at Eingeidnoumlssische Technische Hochschule Zurich (Switzerland), working on the organization of drainage networks in mountain ranges.

Jean Van Den Driessche has a Ph.D. from Montpellier University and completed a State thesis at Paris 7 University in 1994. He then worked on fault-sealing mechanisms in Elf Aquitaine, and since 1996, he has been a professor at the University of Rennes. His teaching and research work concerns tectonics, structural geology, and geomorphology. He has been chief editor of Geodinamica Acta since 1999.

Katia Besnard works on the numerical modeling of water flows and reactive transport in heterogeneous porous media to understand the factors and processes influencing contaminants transport in groundwater flows. She also worked on the physical and numerical modeling of tectonic and sedimentation relationships. She completed her Ph.D. thesis in December 2003 at Rennes University, where she now does postdoctoral studies.

Charles Gumiaux is a structural geologist with particular interests in the application of geostatistics. He worked on three-dimensional lithospheric deformation modeling of the Hercynian domain in Brittany (France) based on tomographic, magnetic, and seismic data analysis. He completed his Ph.D. in April 2003 at Rennes University and is currently doing postdoctoral studies at the Vrije Universiteit, Department of Tectonics (Amsterdam, Netherlands).

ACKNOWLEDGMENTS

This study was supported by Total, who funded Stephane Pochat's Ph.D. thesis, and by the French Ministry of Research and Education for the other authors. We thank in particular J. L. Montenat and S. Raillard, who gave us access to the data on the Niger Delta, and S. Raillard for convincing us to publish this work. Many thanks to K. C. Burke and S. P. Cumella for their very helpful and enthusiastic reviews of the manuscript. We also thank Helen Williams for her corrections of the English manuscript. Finally, we are indebted to the Sedimentology Team in Rennes University for their insightful and mature encouragement that pushed us to further carry our reasoning as independent researchers.

ABSTRACT

A plot of fault throw vs. depth is a simple geometric tool that graphically represents strata thickness variations in growth-fault and growth-fold settings and has previously been used to infer fault kinematics. In this paper, we use it as a prediction tool for lithological change employing only seismic data. If growth faulting is a continuous process, intervals of shale deposition are recorded by unthickened units, while intervals of sand fill in topographic lows. The throw vs. depth plot easily allows depiction of unthickened and thickened sedimentary intervals from even rough seismic records and can therefore be used to predict sand/shale ratios. The method is here applied to a growth fault in the Niger Delta that affects Oligocene to lower Miocene deltaic deposits. Most shale intervals are identified, and the sand/shale ratios are predicted. We suggest that the method can be a valuable tool in oil exploration.

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