Fate of Methane Released From a Destroyed Oil Platform in the Gulf of Mexico

Mauricio Silva,Tarek Abichou,Camilo Roa,Nizar Bel Haj Ali,Ian R Macdonald,Carrie O’Reilly

doi:10.3389/feart.2022.833661

Abstract

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. 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 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. 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. An inverse plume model, calibrated to tracer-gas release, estimated emission into the atmosphere of 9 g/s. 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. 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. 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. Oil rising to the surface was a greater source of methane to the atmosphere than associated gas bubbles.

Highlights

Methane seepage on outer continental margins supports microbial consortia and symbioses that are the basis of chemosynthetic food webs
Methane Release in the Gulf of Mexico will be oxidized to CO2 and its dissociation products (Dickens et al, 1995), or does it reach the atmosphere where it could contribute to greenhouse forcing (McGinnis et al, 2006; Böttner et al, 2020)? Such impacts might increase in future if ocean warming destabilizes marine gas hydrates or aging energy infrastructure
Survey tracklines varied in number and orientation, depending on the orientation and extent of the hydrocarbon plume and the daily operating plan coordinated among research investigators (Supplementary Figure S1A)

Summary

Introduction

Methane seepage on outer continental margins supports microbial consortia and symbioses that are the basis of chemosynthetic food webs. Seeps can be detected acoustically because bubbles are strong reflectors in scanning or swath-mapping sonar (Römer et al, 2012). In the Gulf of Mexico and other oil-generating provinces, seeping hydrocarbons often include oil that rises along with the gas and reaches the ocean surface, where it forms oil slicks that can be detected by remote. Methane Release in the Gulf of Mexico will be oxidized to CO2 and its dissociation products (Dickens et al, 1995), or does it reach the atmosphere where it could contribute to greenhouse forcing (McGinnis et al, 2006; Böttner et al, 2020)? Such impacts might increase in future if ocean warming destabilizes marine gas hydrates or aging energy infrastructure. We have been able to conduct a natural experiment by measuring the properties of a prolific anthropogenic discharge of methane from 135 m when abundant oil was first present, largely removed

Methods

Results

Conclusion