THE MAGNETOTELLURIC METHOD IN THE EXPLORATION OF SEDIMENTARY BASINS

The paper describes the theory of the magnetotelluric (MT) method, and some of the experimental, analytical, and interpretive techniques developed for its use in petroleum exploration in the past five years. Particular emphasis is placed on interpretation, since it is the area least amenable to routine treatment. Whereas present interpretation techniques are adequate, interpretation is the area of both the greatest progress and the greatest need for improvement. Field results are presented from traverses in South Texas bordering on the Gulf of Mexico, and the Anadarko Basin of southwestern Oklahoma. Wide station spacings were used, such as might typify basin evaluations. The South Texas results are compared directly with smoothed induction logs. No useable logs could be found for Oklahoma. Comparisons with known and inferred geology show that the surveys mapped resistivity successfully in the known parts of these basins as well as in portions inaccessible seismically. The capabilities and economics of the MT method justify its consideration for evaluating large unexplored blocks and “no record” areas.