ABSTRACT: Quantitative Models for the Influence of Salt-Associated Thermal Anomalies on Hydrocarbon Generation, Northern Gulf of Mexico Continental Margin

LERCHE, I., Department of Geological Sciences University of South Carolina, Columbia, SC, and A. LOWRIE, Consultant, Picayune, MS

Salt and related structures are important in initiating and storing hydrocarbons along the northern Gulf of Mexico. Using models that allow for both conduction and convection of heat, an examination is given of the thermal patterns associated with various salt features. The focusing and defocusing of heat (due to two-to-three times greater thermal conductivity of salt compared to sediments) are incorporated into the modeling. Results for present day salt and sediment distributions indicate a 30 degrees C greater anomaly above salt features due to thermal focusing, and as much as a 50 degrees C contrast between temperatures within a salt diapir/ridge and a regional sediment column. Calculated rates of salt motion are up to 7 and 17 cm/yr (salt wedge migrating uniformly during Pliocene- leistocene and only during lowstands, respectively during the past 2.5 m.y.) for slope domains, and of order cms/1000 yrs for salt pillows under the inner shelf, coastal plain, and interior basins. Slow moving salt features advance leisurely enough to permit thermal maturation of source rocks (i.e., petroleum production) concomitantly with the moving salt. Source and reservoir could therefore be in the same site.

Rapidly migrating salt moving at about a km in 10,000 yr may outdistance recently produced hydrocarbons. Reservoirs associated with the moving salt (and possibly with fracture-induced permeability as a consequence of the passage of the salt) could then act to entrap the migrating hydrocarbons even though the reservoirs may be in the immature thermal zone.

AAPG Search and Discovery Article #91014©1992 AAPG GCAGS and GC-SEPM Meeting, Jackson, Mississippi, October 21-23, 1992 (2009)