Seepage-Induced
Magnetic
Anomalies Associated with Oil and Gas Fields: Onshore and Offshore Examples
Abstract
The presence of magnetic
anomalies over oil and gas fields has been noted for several decades, but it is only in recent years that the phenomenon has been critically examined. Studies of geologically and geographically diverse regions document that (1) authigenic
magnetic
minerals occur in near-surface sediments over many petroleum accumulations, (2) this hydrocarbon-induced mineralization is detectable in high resolution, broad bandwidth
magnetic
data acquired at low altitude and with closely-spaced flight lines, and in ground
magnetic
surveys, (3) the
magnetic
susceptibility analysis of drill cuttings and near-surface sediments confirms the existence of the aeromagnetic anomalies, (4) sediments with anomalous
magnetic
susceptibility frequently contain ferromagnetic minerals such as greigite, maghemite, magnetite, and pyrrhotite, and (5) approximately 80% of oil and gas discoveries are associated with hydrocarbon-induced
magnetic
anomalies. The association between hydrocarbon seepage and the formation of authigenic
magnetic
minerals in the near-surface has important applications in hydrocarbon exploration. Application of this methodology can quickly identify the areas or prospects with the greatest petroleum potential. Although the discovery of shallow sedimentary
magnetic
anomalies does not guarantee the discovery of hydrocarbon accumulations, it does identify areas requiring more detailed evaluation, thereby focusing attention and resources on a relatively small number of high potential sites. More significantly, these seep-induced
magnetic
anomalies have been documented over many deep-water discoveries in the Gulf of Mexico. Proper integration of near-surface
magnetic
data with geologic and seismic data can improve exploration success and reduce development costs. This presentation will be illustrated with examples from North America (including the deep-water Gulf of Mexico) and Africa.
AAPG Datapages/Search and Discovery Article #90194 © 2014 International Conference & Exhibition, Istanbul, Turkey, September 14-17, 2014