Naudy based automodelling with trend enhancements

Abstract

Recent years have seen a revival of interest in automatic interpretation of magnetic anomalies. This has resulted from a dramatic increase in the quantity and quality of aeromagnetic data, and partly from the development of the "improved Naudy" technique by Shi (1993) (referred to here by the term Naudy). Application of a reliable automatic interpretation method to large aeromagnetic datasets as part of processing allows contractors to produce preliminary maps of structure and depth on a routine basis. This can be done in much the same way as maps of first vertical derivative. In addition, the application of the Naudy technique on an individual line basis allows the interpreter to generate preliminary models rapidly for subsequent refinement by specialised modelling programs. This can reduce much of the setting up time traditionally associated with modelling long, detailed lines of data. One critical parameter that is not determinable directly from the Naudy method is the strike of the body. In parallel with the development of an effective Naudy tool in Intrepid, we have introduced a trend detection method. We use this method to provide strike control during Naudy processing. Body strikes are inferred before the Naudy scanning takes place thereby increasing the reliability of the interpreted models by adding a third dimension. Trends corresponding to shallower and deeper structures are handled independently. Simple two dimensional "dyke" models are constructed with attributes of strike, dip, width, depth and susceptibility. We show examples of the use of the Naudy method to provide a rapid, fully automatic, preliminary structural analysis and depth to basement map of a large petroleum exploration area. The map shows how secondary near-surface fracturing can be seen in the magnetic data. It also shows how pre-application of strike in an area where trends are well defined can significantly improve overall results.