Using Normalized Full Gradient method to interpret gravity anomalies on synthetic and field data

Abstract

Horizontal location and interpretation of gravity anomalies plays an important role in the detection of anomalous bodies and determination of explorative boreholes location. There are various methods for interpreting of gravity anomalies, which commonly use high-pass filters. Among these, Normalized Full Gradient (NFG) method represents the full gradient of the gravity anomaly at a point divided by the average of the full gradient at the datum. This method uses Fourier series to remove deficiencies and eliminate the oscillations which appear on the downward continuation when passing through center of an anomalous body. In this paper, one hypothetical model is considered and a new method is presented to determine the optimum number of Fourier terms, which is used to calculate coefficient of Fourier terms (Bn) based on Filon technique. Then the Bn is used to calculate the NFG. On the vertical and horizontal cross-section maps of NFG, the closed maxima or minima can be used to estimate the depth to centers and horizontal location of mass of possible anomalous bodies (mineral or oil-gas bodies). To evaluate the NFG method, it is applied to the real field gravity data of a known reservoir, and the obtained results compared with the results of independent information arises from drilling and other geophysical methods. Comparison of the results show good agreement and clearly illustrates that the NFG method is able enough to locate anomalous bodies and estimate their burial depth precisely. © 2009 All Rights Reserved by the International Multidisciplinary Scientific GeoConference SGEM.