Formatted Title:

Methylation Potential of Mercury-Impacted Pipeline Scale

Background/Objectives:

Oil and gas reservoirs can contain mercury in different forms that can accumulate in pipelines and processing equipment. Surface facilities can be managed by traditional approaches, but undersea pipelines and other equipment can pose a more difficult management challenge. This study assessed the leachability and methylation potential of mercury-impacted undersea equipment in sediment systems.

Approach/Activities:

The studies were conducted under anaerobic conditions by placing small mercury-containing pipeline coupons in static jars containing 30 g of sediment at near in situ density and moisture content. The mercury-containing scale was also removed completely and incorporated into the sediments as a worst-case scenario to represent mercury after complete corrosion of the pipeline. Total mercury and methylmercury in both sediment and porewater along with other geochemical factors such as redox level, dissolved sulfide, dissolved oxygen and pH in solid and aqueous phase were measured over six months.

Results/Lessons Learned:

The bulk of the mercury in pipeline scale was in the form of mercury sulfide and even in the worst-case scenario less than 0.2% of the total mercury was subject to methylation. The extent of methylation was found to be unrelated to the mass of mercury detectable in the surficial scale by XRF, but instead related to the leachable mercury and was positively correlated with dissolved mercury (passing 0.45 µm filter) (R² = 0.63 and P<0.0001).

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Hasti Ziaei Jam

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