Imaging multiple horizons with spectral techniques in the Sirt Basin, Libya

High resolution aeromagnetic data acquired over the Sirt Basin, Libya, was used to estimate depth to basement, and depth to two intrasedimentary horizons: top of Nubian sandstone, and top of Unit 4 of the Nubian sandstone. Depths to these horizons were calculated through the analysis of energy spectra of the observed magnetic field, while faults and magnetic lineaments were derived through the application of a curvematching method based on the Naudy technique. The project saw the application of a new spectral technique, termed the multiwindow test. When applying energy spectral analysis to windowed potential field data, a poor choice of window size or windowing function will lead to errors in depth estimation. The multiwindow test estimates the depth over a span of window sizes centered over a point of interest; estimates which are not sensitive to window size correspond heuristically to magnetic interfaces. The application of the multiwindow test allowed both rapid, automatic estimation of depth to multiple horizons and also provided a set of windowsizes as suitable candidates for detailed semiautomatic interpretation. The magnetic derived results correlate well with both seismic interpretation and well information. Spectral methods can be successfully applied to image basement and some intrasedimentary horizons in the Sirt Basin, and the multiwindow test has proved itself a valuable tool in producing a robust interpretation of potential field data.