Offshore drilling can disturb the seafloor and generate drilling-fluid deposits, or mud splays, that may affect sensitive benthic habitats or archaeological resources if they extend sufficiently from the well site. To support resource protection, the Bureau of Ocean Energy Management (BOEM) requires avoidance of specified bottom features and implementation of mitigation measures under NTLs 2009-G39 (for water depths <300 m [<984 ft]) and 2009-G40 (for water depths =300 m [=984 ft]); however, the regional footprint of drilling-related seafloor disturbance has not been comprehensively evaluated in over a decade. This study assessed ten previously drilled wells in shallow (<300 m [<984 ft]) and deepwater (=300 m [=984 ft]) settings in the Gulf of America (Gulf; formerly the Gulf of Mexico) to quantify the extent, thickness, and persistence of mud splays across water depths and post-drilling age classes. Integrated geophysical mapping using side-scan sonar and subbottom profiling, combined with targeted sediment sampling and laboratory analyses, characterized surficial and buried deposits and evaluated potential chemical effects. Shallow-water sites exhibited absent or limited splays, consistent with reduced preservation under higher-energy conditions, whereas all deepwater wells displayed discernible seafloor expressions, with several sites containing cohesive buried deposits 18–60 cm thick extending hundreds of meters down-current. Surface sediment chemistry showed no evidence of widespread drilling-related contamination; variability in metals, organic compounds, and radionuclides was primarily associated with sediment grain size, with depth- and proximity-related effects generally limited, analyte-specific, and localized. Most metal, hydrocarbon, and radionuclide concentrations were within regional background ranges, sediment quality benchmark exceedances were infrequent and minor, and no consistent multivariate contamination patterns were identified. Collectively, the findings support the continued applicability of existing shallow-water avoidance guidance and indicate that refinement of deepwater avoidance distances and characterization approaches within the current regulatory framework may better reflect the spatial behavior and persistence of drilling-related deposits in lower-energy environments and enhance protection of sensitive benthic biological and archaeological resources.

USD: $863,278

2023-05-01 → 2026-02-01