The contribution of high quality aeromagnetic survey data to hydrocarbon exploration

Abstract

Aeromagnetic surveys have been flown for fifty years as one of the-methods providing information for hydrocarbon exploration. The method was generally regarded as a reconnaissance tool looking for major structures. Major advances have been made in the last decade in the quality of aeromagnetic data so that low amplitude anomalies arising from magnetic bodies within the sedimentary section can now be measured with sufficient precision to provide information about the geology of the sedimentary rocks associated with hydrocarbon accumulations. This presents a challenge to the interpreter to develop better interpretation procedures to take full advantage of the high quality magnetic data. Recent developments in computer technology, instruments, processing and interpretation of the earth's magnetic field have significantly extended the scope of aeromagnetic surveys as a tool in the exploration for hydrocarbons. The new approach used in the analysis and interpretation of aeromagnetic survey data over sedimentary basins allows interpreters to fully utilise information carried by the magnetic field data. The high quality experimental aeromagnetic survey flown over part of the Eromanga and Cooper basins by Mines and Energy South Australia and Santos, shows that magnetic layers in the sedimentary rocks make this an appropriate area for exploration by detailed aeromagnetic surveys. By applying new interpretation techniques it is now possible to make fuller use of the high quality digital magnetic data. It is possible to delineate major structures within a weakly magnetic basement, to follow magnetic horizons within the sedimentary section, to pick out fault and joint patterns within the sediments, to detect abnormal magnetic regions which may be the result of alterations caused by hydrocarbon seepages and to compute the thickness of the sediments. The aeromagnetic method is very effective for interpolating between widely spaced seismic lines that are used to tie the magnetic interpretation to the stratigraphy. The depth to basement estimates made in this way are comparable with those derived from seismic survey data. Since the completion of the experimental research the methods developed have been successfully applied to several basins including ones in low latitudes, rugged terrains and volcanic provinces. The new approach to interpretation of aeromagnetic survey data is providing petroleum companies with quick, comprehensive and cost-effective tools for first- pass exploration. The non-invasive nature of the surveys makes them ideal for use in difficult terrains and in politically and environmentally sensitive areas.