Paper Summary
The Gulf of Mexico is one of the most prolific oil and gas basins in the world. Understandably, the region is also home to many deeply buried mature source rocks and migration pathways to the surface, which result in petroleum seepage on the seafloor.
Seeps occur as gases, liquids, asphalts, and tars. These variable mixtures of hydrocarbons generally seep under low pressure and slow rates of release and are altered by chemical processes that happen on the seafloor. Consequently, as seafloor seepage takes place, both the biological and chemical properties of the sediments around the leakage area are altered.
As chemically reduced fluids rise from subsurface depths, they encounter sulfate-rich oxygenating fluids near the seafloor. The ensuing chemical reactions lead to the precipitation of minerals—for example, carbonate precipitates form crystals, nodules, and cemented sediments over sedimentary veins and fissures—reducing the seepage.
The emerging mineral-rich fluids invite microbes, mollusks, and clams to feed on them, and these communities located around the seep locations form hard surfaces that appear different from the surrounding seafloor. Such hard surfaces are acoustically reflective and can be detected using modern technology.
It doesn’t take a high level of oil seepage from an offshore oilfield to be detected. Active and inactive hydrocarbon seeps on the seafloor can be identified.