Processes impacting deep-water, subsalt, foldbelt hydrocarbons

Lowrie, Alan, Consultant, Picayune, MS; Linda Jenkins, Susan Moffett, Picayune, MS; Thomas Klekamp, and Ian Lerche, University of South Carolina, Columbia

Abstract

A brief compilation of geologic processes, both subsalt and deep water, is presented. A potential impact of the downdip, basinward migration of the Sigsbee Salt complex on petroleum generation is also discussed. The processes include: hydrates and hydrodynamics of hydrate stability zones, implications of salt-floored basin evolution, earthquakes and paleo-fracture zones with thermal anomalies, migrating Louann salt, fracture development and gas expansion/contraction, fanfold belt development, subsalt pressure compartments, and major (as high as a thousand fold) changes in deposition rates from highstand to lowstand during the Quaternary, and probably Neogene.

The purpose is multi-fold: (a) focus awareness on multiplicity of major processes operating, and (b) present preliminary notions of synergy between processes. With large variations in deposition rates between high and low sea level stands, the rates at which processes operate over time are highly variable. Thus, results over time are also variable. Synergy between processes, including those related to specific zones, i.e. subsalt and basement, is connected by the multi-fold sedimentation rate variation and the rate and extent of the basinward advance of the Sigsbee salt complex through the growing sedimentary wedge. The impact of such accelerated geology on hydrocarbon accumulation and exploration needs investigating.

Salt is known to have double to triple the thermal conductivity of alternating sand and shale beds. Thus, salt massifs, ridge, and diapirs can be up to 20° - 40° C hotter than the surrounding sediments. The advancing salt can thermally mature whatever organic materials have been deposited in the sedimentary wedge and make them available for accumulation in reservoirs within the continuously growing salt-floored subbasin.