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Abstract

AAPG Bulletin, V. 88, No. 3 (March 2004), P. 303-324.

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

Flow units, connectivity, and reservoir characterization in a wave-dominated deltaic reservoir: Meren reservoir, Nigeria

D. K. Larue,1 H. Legarre2

1ChevronTexaco Exploration and Production Technology Company, San Ramon, California 94583; [email protected]
2ChevronTexaco Overseas Petroleum Company, Lagos, Nigeria

AUTHORS

Dave Larue has worked for ChevronTexaco Corporation for the past six years studying sequence stratigraphy and geologic modeling. Formerly, he worked at Exxon Production Research. Prior to joining the oil industry, he was a professor at the University of Puerto Rico and an original member of "los Profesores," a rock-and-roll band that toured the western part of the island for several years. He received his Ph.D. from Northwestern University and was the last Ph.D. student of Larry Sloss, the father of sequence stratigraphy. He is an AAPG Visiting Petroleum Geologist and member of the AAPG Distinguished Lecturer Selection Committee.

Henry Legarre received his M.S. degree from San Diego State University. He started working at ChevronTexaco in 1991, after spending some time at Scripps Institution of Oceanography, and Woods Hole Oceanographic Institute. He has worked for ChevronTexaco as an Earth scientist in California (Bakersfield, La Habra, and San Ramon), Luanda, Angola, and is currently in Lagos, Nigeria. His areas of expertise are production geology, geochemistry, carbonate and clastic stratigraphy, reservoir characterization, and geologic modeling. He has also been the chairman of the AAPG Student Chapter Committee and serves on the AAPG Grants-in-Aid Committee.

ACKNOWLEDGMENTS

George Mattingly was a strong field mentor and helped us conceive and complete this study. Fetze Papa checked and normalized all well logs. Dayo Adeogba has remained a continuing source of information and checks to our interpretations. The core description in Figure 3 is based on a study by Bryan Bracken of Chevron Texaco. Stratigraphic and other discussions with Frank Harris, John Toldi, Julian Thorne, Deyi Xie, Feng Jian, Alex Castellini, June Gidman, Marge Levy, Jorge Landa, and Tim McHargue provided a great breadth of viewpoints and insights. Doug Goff reinterpreted the sequence boundary shown in Figure 7. Gerry Cook and Adwait Chawathe helped drive our geologic interpretations into flow engineering studies. Tom Tran and Dave Goggin provided timely advice in geostatistical modeling. Working with one of us (D.K.L.) and Ron Behrens of ChevronTexaco, Sebastien Morpourgo developed the Gocad connectivity program described herein, Connie Terricola and Karen Payrazyan developed the path length program, and Remi Moyen developed an advanced geobody program. We appreciate the help of John Garrity for continued support regarding acquisition of information on the Meren and Malu fields. We thank Chevron Nigeria Limited and the Nigerian National Petroleum Corporation for permission to publish this work. Reviews by Frank Ethridge, J. R. J. Studlick, and Alan Reed were helpful. We are especially grateful to Jeff Warner and Rick Esenberg who helped in the final editing. Adedokun A. Odunsi provided us with recent production data for the Meren reservoirs.

ABSTRACT

The Meren E-01 (Agbada Formation, middle Miocene) reservoir offshore Nigeria consists of a lower progradational shoreface succession terminated by a minor sequence boundary, overlain by a progradational and retrogradational shoreface succession. Deposition occurred in a wave-dominated delta front, as indicated by the presence in core of hummocky cross-beds, slumped units, and turbidites. Eight flooding surfaces were correlated, and isopach maps, sandstone-quality trend maps, and mudstone-quality trend maps were constructed for each parasequence. This work revealed a complex reservoir architecture characterized by shoreface clinoforms and a history of progradation and retrogradation cycles.

Three different three-dimensional geological characterizations of the E-01 reservoir were built: a geostatistical model that used only well data; a more geologically complex facies-based model that used the sandstone-quality trend maps in addition to well data; and the most geologically complex sequence-stratigraphic model that used mudstone-quality trend maps in addition to the above data. The three models were analyzed in terms of sandstone continuity and connectivity to hypothetical injector and producer wells. Only the sequence-stratigraphic model predicted significant vertical compartmentalization through tortuosity generated by flooding-surface mudstones. Waterflood fluid-flow simulation of a downdip sector of the geologic models predicts similar recovery for the three models, but a significantly different distribution of unswept oil. Only the sequence-stratigraphic model identified parasequences with abundant unswept oil that are large enough to be economic infill prospects. History-matched, full-field fluid-flow simulations verify both the reservoir compartments predicted by the sequence-stratigraphic model and infill targets.

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