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AAPG Annual Convention and Exhibition

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Previous HitMagneticNext Hit Bright Spots Can Identify the Most Prospective Deepwater Areas and Prospects

Abstract

The presence of Previous HitmagneticNext Hit anomalies over oil and gas fields has been noted formdecades, but only in recent years has the phenomenon has been critically examined. Studies of geologically and geographically diverse regions document that (1) authigenic Previous HitmagneticNext Hit minerals occur in near-surface sediments over many petroleum accumulations, (2) this hydrocarbon-induced mineralization is detectable in high resolution, broad bandwidth Previous HitmagneticNext Hit data acquired at low altitude and with closely-spaced flight lines, (3) the Previous HitmagneticNext Hit susceptibility analysis of drill cuttings confirms the existence of the aeromagnetic anomalies, (4) sediments with anomalous Previous HitmagneticNext Hit susceptibility frequently contain ferromagnetic minerals such as greigite, maghemite, magnetite, and pyrrhotite, and (5) 80% or more of offshore deep-water oil and gas discoveries in Gulf of Mexico are associated with these shallow, sedimentary hydrocarbon-induced Previous HitmagneticNext Hit anomalies. The association between hydrocarbon seepage and authigenic Previous HitmagneticNext Hit minerals has important applications in deep-water hydrocarbon exploration. Seep-induced sedimentary Previous HitmagneticNext Hit anomalies, known as Previous HitMagneticNext Hit Bright Spots (MBS), can reliably identify areas and prospects with the highest petroleum potential in water depths as great as 9000 feet (2800 m). The high-resolution cesium vapor aeromagnetic data used in this study were acquired between 1986 and 1992, and extend from East Breaks to Viosca Knoll in the Gulf of Mexico. A comparison of the processed and interpreted aeromagnetic data with post-survey drilling results documents that 89% of wells drilled on prospects within or adjacent to Previous HitMagneticTop Bright Spots have resulted in commercial discoveries. In contrast, fewer than 30% of wells drilled on prospects located more than 800 m from the MBS have resulted in discoveries. Furthermore, MBS areas account for 65% of production – almost 5 times that from within salt-covered areas where no MBS could be determined, although the areas are roughly similar in size. Although the discovery of MBS anomalies does not guarantee the discovery of commercial oil or gas, it does identify areas requiring more detailed evaluation, thereby focusing attention and resources on a relatively small number of high potential sites.