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AAPG Special Volumes
Abstract
13. An Automated Method for Inferring 3-D Salt Movements from the Suprasalt Sedimentation Pattern
Reinold R. Cornelius,1 Lawrence M. Cathles III,2 Alex Erendi2
1GSCI Consulting, Austin, Texas, U.S.A.
2Cornell University, Ithaca, New York, U.S.A.
ACKNOWLEDGMENTS
We are grateful to Jacqueline E. Huntoon for suggesting that differential sedimentation rates could be used to infer the rates of salt rise in the early stages of this project more than nine years ago. We thank ARCO Research for providing the interpreted sections used in this study to the Global Basins Research Network (GBRN). We thank Mark G. Rowan for providing original-scale copies of his sections for this study, as well as for discussions and for sharing his insights. The fluid-flow calculations were greatly facilitated by the initial work of Franois-Dominique Cipriani and the tireless advice and guidance of Paul D. Manhardt, CEO of GeoGroup, Inc., formerly of Computational Mechanics Corporation, and a finite-element expert. We thank Richard Buffler, who provided one of us (R.R.C.) with laboratory space and library access. The manuscript was very much improved by the thorough reviews and constructive comments of two AAPG reviewers, Chris Travis and an anonymous reviewer. We thank them for their efforts.
Although efforts to model regional salt redistribution started under the DOE Pathfinder project, support for the work reported here was provided almost entirely by the Gas Research Institute (GRI Grant No. 5097-260-3787) and the corporate sponsors of the GBRN. We are immeasurably indebted to these institutions for their support.
ABSTRACT
The formation and diapiric destruction of salt canopies have a direct impact on fluid flow and hydrocarbon migration
in areas such as the Gulf of Mexico. Inferring the history and pattern of salt redistribution in even a local area can be time-consuming and is subject to uncertainties of many kinds. We demonstrate in this chapter that it is possible to infer the gross 3-D pattern of salt redistribution and the time when salt welds form directly from the sedimentation pattern and the present position of salt welds. The algorithm is based on the simple assumption that after isostatic adjustment is taken into account, accommodation space in areas with greater than average sediment loading is provided by salt movement to areas of less than average sediment loading. Although the algorithm is crude in several regards and could be improved by interpreter intervention, we show that the 2-D history of salt redistribution it estimates is almost identical to published salt
migration
histories inferred by conventional means in one test area. Applying the methods to a 20-
50-km area in the offshore Louisiana Gulf of Mexico, we find that the 3-D simulation estimates salt-weld formation at significantly later time in the Eugene Island Block 330 area (0.45 versus 1.3 Ma) than 2-D simulations. The later time is more compatible with geochemical indications of late filling for the Eugene Island Block 330 reservoirs. The estimated timing of salt-weld formation does not depend on the present thickness of salt. Modeling subsalt pore-water movement through microdarcy subsalt strata indicates that brines can be drawn to early-opening salt from distances of 50 km or more.
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