Local Sedimentary Structure and Regional Linear Trends Indicated by an Airborne Micromagnetic Survey of the Texas and Louisiana Gulf Coast

Land, John P.

The data used in this presentation was acquired in the early 1950's by Aero Service Corp. under contract to Alcoa, the Aluminum Company of America. The 45,000 square mile program was designed, directed and interpreted by Dr. W.P. Jenny, Geological and Geophysical Consultant and originator of the Micromagnetic method who, at that time, looked at local, high frequency and low amplitude magnetic anomalies as evidence of the local structuring of shallow formations having different magnetic properties. His work, nevertheless, did provide specific targets for the standard detailing methods - gravity, Subsurface Geology and, in those days, 2-D Seismic, to investigate.

We now recognize these local features as a low amplitude, high frequency element of the magnetic field most often related to near-surface differences in mineralogy that accompany hydrocarbon microseepage. Any such prospect leads can then be systematically evaluated by a program of magnetic susceptibility measurements. If those measurements are anomalous, soil samples are taken for geochemical analysis as to the presence of hydrocarbons.

The paper presents before-and-after examples of anomalies and subsequent drilling as a way of evaluating the airborne micromagnetic method's abilities in the coastal sector of Texas and Louisiana. And, the opportunity is taken to display a regional linear system of near-surface anomalies presently under study.

Though the overall the methodology of the follow-up to the airborne survey was less effective than what we would now apply, the path that was taken led to a very successful drilling program. Over a 12 year period, Alcoa drilled a total of 316 wells. Of these, 198 or 63% were commercial. The system, one which initiated the exploration of a region by using airborne micromagnetics to describe prospect leads, was considerably more successful than the norm. If surface geochemistry had been used to evaluate those leads, the discovery rate would undoubtedly have been even higher.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013