AAPG Bulletin, V. 82 (1998), No. 2 (February 1998), P. 228-250.

Physical Modeling of Structures Formed by Salt Withdrawal: Implications for Deformation Caused by Salt Dissolution¹

Hongxing Ge² and Martin P. A. Jackson³
 

©Copyright 1998.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received July 11, 1996; revised manuscript received February 18, 1997; final acceptance September 11, 1997.
²Bureau of Economic Geology and Department of Geological Sciences, University of Texas at Austin, Austin, Texas 78713. Present address: Shell E&P Technology Company, Bellaire Technology Center, P.O. Box 481, Houston, Texas 77001; e-mail: [email protected]
³Bureau of Economic Geology, University of Texas at Austin, Austin, Texas 78713.

All models were run at the Applied Geodynamics Laboratory of the Bureau of Economic Geology, University of Texas at Austin, with financial support from the following companies: Agip S.p.A., Amoco Production Company, Anadarko Petroleum Corporation, ARCO Exploration and Production Technology and Vastar Resources, BP Exploration, Chevron Petroleum Technology Company, Conoco and Dupont, Exxon Production Research Company, Louisiana Land and Exploration Company, Marathon Oil Company, Mobil Research and Development Corporation, Petroleo Brasileiro S.A., Phillips Petroleum Company, Société Nationale Elf Aquitaine Production, Statoil, Texaco, and Total Minatome Corporation. The Department of Geological Sciences and the Geology Foundation at The University of Texas at Austin and Phillips Petroleum Foundation provided additional financial support for Hongxing Ge. Sharon Mosher, Bruno Vendeville, Mike Hudec, William Kilsdonk, Louis Liro, Carl Fiduk, Martha Withjack, Robert Evans, and Richard Groshong provided invaluable discussions or comments. The paper was edited by Amanda R. Masterson and Tucker Hentz. Publication was authorized by the Director, Bureau of Economic Geology, University of Texas at Austin. 

ABSTRACT

By creating 15 physical models, we investigated deformation above subsiding tabular salt, salt walls, and salt stocks. Dry quartz sand simulated a brittle sedimentary roof above viscous silicone representing salt. The modeled diapiric walls had linear planforms and rectangular, semicircular, triangular, or leaning cross sectional shapes; the stock was cylindrical.

In models where the source layer (or allochthonous salt sheet) was initially tabular, a gentle, flat-bottomed syncline bounded by monoclinal flexures formed above a linear zone where the silicone was locally removed. Above all subsiding diapirs, the deformed roof was bounded by an inner zone of steep, convex-upward reverse faults and an outer zone of normal faults. Above subsiding diapiric walls, extensional and contractional zones were balanced. Above the subsiding salt stock, conical, concentric fault zones comprised inner reverse faults and outer normal faults.

Sediments were added both before (prekinematic) and during (synkinematic) salt withdrawal. In entirely prekinematic roofs, reverse fault zones and normal fault zones both widened with time. Reverse faults propagated upward from the corners of the withdrawing diapirs. New reverse faults formed in the footwalls of reverse faults, each nearer the center of the deepening roof trough. Conversely, new normal faults formed successively outward from the sagging trough. Synkinematic deposition retarded faulting, but the pattern of inner reverse and outer normal faults was repeated; however, reverse faults formed successively outward, whereas normal faults formed inward.

New conceptual models suggest that salt dissolution forms similar structures to those physically modeled for salt withdrawal. The appropriate physical models resemble natural dissolution structures above tabular salt. Extension alone above diapirs is not caused merely by salt withdrawal or dissolution, but by regional extension or active diapirism.