Chapter 5: Surface and Subsurface Expression of Hydrocarbon Seepage in the Marco Polo Field Area, Green Canyon, Gulf of Mexico
Harry Dembicki, Jr., David L. Connolly, 2013. "Surface and Subsurface Expression of Hydrocarbon Seepage in the Marco Polo Field Area, Green Canyon, Gulf of Mexico", Hydrocarbon Seepage: From Source to Surface, Fred Aminzadeh, Timothy B. Berge, David L. Connolly
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Seep features in the area of the Marco Polo field in the Gulf of Mexico were identified using remote sensing, conventional seismic data, and high-resolution geophysical data collected from an autonomous underwater vehicle (AUV). Using these data, the potential seep features were mapped based on their geomorphology and acoustic characteristics. Results show that a mud volcano and a mud mound field had the highest probability of macroseepage, confirmed by subsequent sampling and analysis of seafloor sediments. The 3D seismic data in the area around the Marco Polo field were also processed to highlight gas chimneys. Chimneys were highlighted using a neural network approach with directional seismic attributes. The chimney processing results showed evidence of chimneys that should provide vertical hydrocarbon migration pathways through the salt canopy. These chimneys directly underlie the Marco Polo field and provide a mechanism for charging the field. The processing also showed fault-related chimneys on the flank of the Marco Polo field. These chimneys correlate to mud mounds and a mud volcano, detected by the AUV data. The surface features associated with the chimneys contain hydrocarbon seepage, based on surface sampling. Good conformance between chimney and seafloor indications of seepage reinforces the relationship between the seeped hydrocarbons and the subsurface reservoir. These combined data have the potential for assessing seepage flux rates as well as quantifying the risk for hydrocarbon charge and seal. The work demonstrates that chimney processing and interpretation used in conjunction with seep detection has the capability to improve risk assessment in mature and frontier basins.
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With the increased resolution power of many geophysical methods, we are seeing direct evidence of seeps on a wide variety of data, including conventional seismic. New methods and technology have also evolved to better measure and detect seeps and their artifacts and reservoir charge and to map migration and remigration routes. In addition, detection of seepage is important for minimizing the risks associated with shallow gas drilling hazards, ensuring platform stability, and preventing well blow-outs.