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ABSTRACT: Salt Dynamics: Simulation of Mushroom Caps on Salt and Relations to Hydrocarbon Accumulations

Z. Yu, Ian Lerche

Various shapes of moving salt were simulated in response to gravity contrast and tectonic movement, and the deformations and fractures of the surrounding sediments were examined. The varying parameters in the model include the critical burial depth of the salt base, the overhang depth of the salt cap, the salt body's size, the salt speed, and the sediment depositional rate, as well as variation of the surrounding rock properties with depth, such as Lame constants, shearing strength, and internal friction. Mohr's criterion for failure was applied, allowing an indication of where fractures occur and their orientations.

Including the thermal effects of salt yields features favorable to hydrocarbon accumulation sites as shown by the simulations. (1) Fractures happening near the vertical salt body and below the mushroom cap salt provide a continuous pathway for hydrocarbon migration due to the enhancement of permeability. (2) The overhanging cap salt sheet provides a good chance of trap formation in terms of seals. (3) The thermal effect of salt enhances the maturity of the source rocks. (4) The observed faulting behaviors around salt are accounted for by primary and secondary fractures, as exhibited through the simulations.

Natural case history examples provide a degree of confidence in the simulation results, which are of great use for future exploration predictions.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990