An evaluation of electrical methods applied to petroleum exploration in Australia

Abstract

The use of electrical prospecting methods for petroleum exploration has been under study for the past few years. Bipole-dipole and dipole-dipole induced polarization (IP) surveys have been tested over a number of oil and gas fields and prospects in the Denison Trough, and the Bowen, Cooper and Surat Basins. Self potential (SP) methods have also been tested over a number of prospects; the details of a computer-aided data acquisition system are the subject of another publication. Definite resistivity anomalies are seen over the fields. These are discussed with the induced polarization (chargeability) data. The data from two SP surveys show that significant negative anomalies occur above hydrocarbon deposits. From this work it appears that the most definitive parameter to measure is the apparent resistivity, although measurement of the chargeability parameter is worthwhile because anomalies in both often correlate with hydrocarbon-bearing structures. The significance of the correlation between anomalies in both SP and IP data and hydrocarbon accumulations necessitates a description of the processes that produce the anomalies. The SP anomalies are caused by large scale redox (oxidation-reduction) cells formed in a plume above trapped hydrocarbons. These active cells have slightly altered the lithology above hydrocarbon traps; the mechanism is electrochemical in nature, using energy from the hydrocarbons that escape past the imperfect cap rock.