From Satellite Images to Reservoired Hydrocarbons: The In-Depth Investigations of the Marco Polo Seeps, Green Canyon, Gulf of Mexico
The search for seafloor hydrocarbon seeps is frequently an integral part of deepwater exploration programs. If thermogenic hydrocarbons are found at the seafloor, exploration risk can be mitigated by the seeps providing evidence of a working petroleum system. The recovered seeped hydrocarbons can then be used to discern the contents of the subsurface reservoir and provide clues about their origin. This was the case for Anadarko Petroleum's exploration efforts in Green Canyon Blocks 607 and 608 that resulted in the discovery of the Marco Polo oil field. The initial seep study included using synthetic aperture radar (SAR) satellite imagery to look for sea surface slicks, processing the 3-D seismic data for seafloor attributes to help recognize potential seep features, sampling these features with piston coring, and geochemically analyzing the recovered core material. While most studies of seafloor seeps end at this point, many aspects of the Marco Polo seeps have been the subject of further investigations. These studies have included: gas chimney processing of the seismic data; a high resolution geophysical survey using an autonomous underwater vehicle (AUV) that acquired detailed multibeam bathymetry, side scan sonar, and sub-bottom acoustic profiling over the seep area; resampling the original seep features, as well as sampling potential seep features in adjacent areas; and in-depth geochemical analysis of the sediments and seeped hydrocarbons recovered. This presentation will review some of the results of these investigations. It will demonstrate how seafloor seep features can be more easily recognized and how this can lead to improving the sampling of the seep features. It will also show how detailed geochemical analysis, including comparisons to the background organic matter and reservoired oil, can provide better evidence for identifying the origin of the seeped hydrocarbons encountered and understanding their exploration significance. And finally, it will illustrated how examining the cores for the presence of authigenic carbonates, chemosynthetic organisms, and other features can help characterize the seep sites.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017