![]() ![]() Seafloor microbial mats morphologically resembling sulfide-oxidizing bacteria surrounded areas of bubble ebullition. ![]() Elevated methane concentrations in bottom water above and down current from the seep decreased to background seawater levels in the mid-water column >200 m above the seafloor. Video evidence of an active hydrocarbon seep was confirmed by methane and hydrocarbon analysis of the overlying water column, which is 260 m at this site. A hydrocarbon seep near Scott Inlet, Baffin Bay, was visited for in situ observations and sampling in the summer of 2018. Seabed hydrocarbon seeps present natural laboratories for investigating responses of marine ecosystems to petroleum input. The total equivalent volume of gas within these bodies is estimated to potentially be as large as 1.5 gigatons or 10.5 TCF, considering uncertainty for estimates of porosity and saturation, comparable to the entire proven natural gas reserves of Trinidad and Tobago in 2019. Observations of gas in a nearby well, other indicators of hydrate in the vicinity, and regional geologic context, all support the interpretation that these large bodies are composed of hydrate. Directly underneath these bodies lies a zone of poor reflectivity, which is both typical and expected under hydrate. We believe that these lower acoustic values are representative of gas hydrate and not of salt. Further investigation reveals that using lower-valued acoustic velocities results in higher quality images with little or no moveout. However, when seismic images are constructed using acoustic velocities associated with salt, the resulting images were of poor quality containing excessive moveout in common reflection point (CRP) offset image gathers. We originally interpreted these bodies as salt, as they share common visual characteristics on seismic data with shallow allochthonous salt bodies, including high-impedance boundaries and homogenous interiors with very little acoustic reflectivity. In the southwestern Gulf of Mexico, reanalysis of 3D seismic reflection data reveals evidence for the presence of six potentially large gas hydrate bodies located at shallow depths below the seafloor. Oil rising to the surface was a greater source of methane to the atmosphere than associated gas bubbles.Īs rising ocean temperatures can destabilize gas hydrate, identifying and characterizing large shallow hydrate bodies is increasingly important in order to understand their hazard potential. Atmospheric methane concentrations were elevated 1–2 ppmv over baseline when the ship was stationary within the surfacing plumes of gas after oil was removed from the flow. The CRDS detected transient peaks of methane as high as 15.9 ppmv ppm while oil was being recovered to a ship from underwater storage tanks. In 2021, the containment system allowed gas to escape into the water at 120 m depth after passing through a separator that diverted oil into storage tanks. An inverse plume model, calibrated to tracer-gas release, estimated emission into the atmosphere of 9 g/s. Continuous air sampling with a cavity ring-down spectrometer (CRDS) over the release site detected atmospheric methane concentrations as high as 11.7, ∼6 times greater than an ambient baseline of 1.95 ppmv. In 2018, prior to containment, oil and gas bubbles formed plumes that rose to the surface, which were quantified by acoustic survey, visual inspection, and discrete collections in the water column. Discharge continued largely unabated until 2019, when findings partly reported herein prompted installation of a containment device that could trap oil before it entered the water column. In 2004, destruction of a Gulf of Mexico oil platform by Hurricane Ivan initiated a discharge of oil and gas from a water depth of 135 m, where its bundle of well conductors was broken below the seafloor near the toppled wreckage.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |