Because magnetic minerals may directly indicate the presence of oil and gas deposits, magnetic methods are applied to hydrocarbon exploration in oil-bearing sedimentary basins. The basic problem in applying these methods is the isolation of weak magnetic anomalies sourced by low concentrations of the magnetic minerals present. These weak anomalies are often masked by much stronger magnetic anomalies caused by underlying magnetic rocks and/or by rocks in the basin sediments. Weak local anomalies can efficiently be isolated by applying selective 1-D digital frequency filters. The method of filtering has been checked by data obtained using simple models of magnetic sources and using a model representative of the local geology in our study area in the southern Pannonian basin, Yugoslavia. The magnetic field frequency content was analyzed by applying the power spectral density estimation, using the maximum entropy method. The digital filters were designed using the window function method. The best results were obtained by the Kaiser window function for the chosen range of the band-pass filter.
In our study area, the isolated local magnetic anomalies have amplitudes of ±10 nT and trend in an east–west direction parallel to the predominant structural grain. These anomalies correlate very well with the known oil and gas fields. As an example, filter processing of magnetic anomaly data, combined with the 3-D seismic data gained in the filtered magnetic field, correlate well with one of the oil fields. The next phase of the project will concentrate on the anomalies occurring outside the established gas and oil fields.