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4 - Gravity and Magnetics

Published online by Cambridge University Press:  25 November 2021

By
Alan B. Reid
Edited by
Hamish Wilson ,
Keith Nunn  and
Matt Luheshi
Hamish Wilson
Affiliation:
BluEnergy Ltd
Keith Nunn
Affiliation:
Nunngeo Consulting Ltd
Matt Luheshi
Affiliation:
Leptis E&P Ltd
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Summary

The gravity and magnetic survey methods have been in use since the early days of geophysical prospecting for petroleum. They find most application in frontier exploration. In that context, regional and global datasets are often available to assist with early evaluations.

The design and execution of modern, targeted surveys has been transformed as a result of advances in instruments and the advent of satellite navigation. Imaging and interpretive techniques have been transformed by modern computer-based approaches. The potential field methods are extremely cost-effective at delineation of basins and determining structural controls on those basins, especially delineating normal faulting within rift basins. Magnetic surveys yield depth to basement and delineate any igneous rocks present. Such surveys therefore enable early decisions about cost-effective placement of seismic surveys and other intensive follow-ups.

In more mature exploration, gravity and gravity gradient data combine well with seismic data in distinguishing between alternate interpretations, thereby removing ambiguities. High-resolution magnetic data offer an effective means of fault connection in conjunction with regional seismic coverage, if shales or mudstones are present.

In a production environment, gravity logging is the most sensitive density log available, and 4D-gravity finds application in gas production and also water-flood monitoring.

Keywords

basementbasement depthdeconvolutiondensityfaultsgeoidgravitymagneticmagnetitepotential fieldregional geologystructuresusceptibility
Type
Chapter
Information
Integration of Geophysical Technologies in the Petroleum Industry , pp. 71 - 123
Publisher: Cambridge University Press
Print publication year: 2021

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