High Resolution Airborne Micromagnetics Used to Describe Initial Prospect Leads in the Development of Oil and Gas Drilling Prospects in the Transition Zone of the Gulf Coast

J. P. Land, J. D. Lazor, and R. L. Coons

Light hydrocarbons escape from petroleum reservoirs and move in a vertical to near-vertical path to the surface in gas migration chimneys or microseeps. Accompanying geochemical processes create locally anomalous rock properties in the overlying near-surface formations that are geophysically measurable. Depending on the chemical elements involved, the result of such alteration is either an enrichment or a destruction of magnetic minerals present which changes the magnetic susceptibility of the sediments creating either positive or negative magnetic anomalies.

Because local, near-surface magnetic anomalies may also be caused by depositional processes or the structuring of the sediments, the paper describes the systematic follow-up used to evaluate each magnetic anomaly. The initial goal is to determine whether or not the magnetic anomaly signifies an alteration zone and if so, to see if an active hydrocarbon microseep is measurable.

The purpose of the paper is to demonstrate the potential of a high resolution airborne magnetic survey to provide not just a more detailed picture of intra-sedimentary and basement structure and topography but, to also present a perspective of the region’s nearsurface structural grain and, most importantly, specific targets identified as seep-related and thus worthy of the great expense of leasing and subsurface and seismic definition. Such magnetic surveys contribute to a quicker focusing on viable drilling prospects, a basic objective of any exploration program.

Examples presented illustrate the efficiency of systematic multidiscipline exploration and the role played by micromagnetic-styled high resolution magnetic surveys in Transition Zone programs.

AAPG Search and Discovery Article #90901©2001 GCAGS, Annual Meeting, Shreveport, Louisiana