Modeling Salt Tectonic Evolution and Sedimentary Fracturing along Northern Gulf of Mexico
LOWRIE, ALLEN, Consultant, Picayune, MS, and Z. YU and I. LERCHE, University of South Carolina, Columbia, SC
Massive hydrocarbon reservoirs associated with salt features along the northern Gulf of Mexico prompts interest into the synergistic and dynamic evolution of the two features. Use of geologic models from the evolution of salt movement in the northern gulf provides constraints on movement rates. Salt originally deposited some 150 Ma on continental crust, i.e., South Louisiana basin, migrating to present position along Sigsbee Escarpment, would, on average, move at 0.3 cm/yr; or, if movement occurred only during lowstand, at 0.5 cm/yr. If extruded salt lay along present shelf-break during Upper Miocene-Pliocene (10 to 2.5 Ma), then the extrusion rate would be, on average, 7 cm/yr and, during lowstand only, 17 cm/yr. Under the slope, salt is suggested to respond isostatically to new depo ition, yielding a vertical migration rate of cms/yr, given sedimentation rates of a kilometer per single fourth order (Milankovitch) lowstand. Under the shelf, buried salt apparently moves by buoyancy at cms/1000 yrs.
Given this model for salt tectonic rates, it is possible to examine domains of primary and secondary fracturing, using Mohr's criteria for failure, surrounding salt features of the Louisiana offshore.
It is shown that (1) the higher the rate of salt motion, the larger the range of fracturing; (2) the domain of fracturing around salt features depends on salt size, sediment properties, and salt speed. Generally the fracturing domain extends 2-4 km in the vertical direction, and 3-5 km in the lateral direction.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)