A Biomarker-Based Approach Identifying Contaminated Sediments as the Primary Source of Oil Sheen at Mississippi Canyon Block 20

Forensic Environmental Chemistry
Oral Presentation

Prepared by

Contact Information: [email protected]; 858-414-6787


Identifying the location(s) and primary source(s) that create on-going sheen near the Taylor Energy Company MC20 production platform presents one of the most non-traditional, chemical forensic studies in history. The MC20 site differs from the norm as approximately 20 different “source” oils were released following the platform casualty. After the platform toppled, oil immediately contaminated local bottom sediments, the water column, and the sea surface, and continued to do so until well intervention operations were completed. Field studies conducted in 2012/2013 helped reveal potential seafloor source(s) location(s) of on-going surface sheens as two zones of heavily contaminated sediment on the seafloor; the former well-bay area and a confined area near the location of the toppled jacket. Other locations sampled at the same time, even within six meters of these heavily contaminated areas, had much lower concentrations of total petroleum hydrocarbons. In 2017, we returned to the site and collected ~60 surface sheens on nine field days over a six-week period. Individual surfacing expressions were targeted and the location and time of surfacing was recorded. Concurrent with sheen collections, water column currents were measured with seafloor mounted ADCPs and multibeam imagery of water column anomalies was collected from a surface vessel. Based on analysis of biomarkers, surface sheens are chemically heterogeneous, do not appear to be from a single oil, and are most similar to the highly contaminated chemically heterogeneous sediments near the toppled jacket. We argue that the sheen is driven by releases from the remnant oil in the sediments and different surfacing locations of the sheen are driven by currents. Biomarker-based results were also used for a mass-balance-based approach that further supports that the source of on-going sheens is remnant oil in the sediment and not a leaking well(s).