Mercury rising in Gulf of Mexico structure removals

Mercury, typically found in high concentrations in hydrocarbons in southeast Asia and South America, has been “popping up” more often in deepwater projects in some areas of the Gulf of Mexico, according to Tim Jenkins, Principal Engineer at PEI.

PSC's Louisiana facility grants easy access to the waterways leading from the Gulf of Mexico (Image credit: PSC)

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In one recent project for an offshore operator in the Australasia region, the Houston-based contractor removed 418 grams of mercury from equipment that was loaded with 4g/m2 of the toxic metal, Jenkins said in a speech at the recent 8th Decommissioning & Abandonment Summit in Houston.

PEI has determined that mercury’s impact on equipment and piping can be reversed by pulling the mercury out of the systems and restoring them for re-use or decommissioning, Jenkins said. He added: “You must do the science first and understand your chemical- and reduction-processing plan”.

Jenkins was not the only person to show off new developments in decontamination to the annual conference. Rick Wimberley gave insight into a new facility opened by PSC Industrial Outsourcing in Gibson, Louisiana to decontaminate and disassemble platforms brought in from the Gulf of Mexico (GoM).

Removal about more than just equipment

When removing equipment from the GoM, any number of contaminants can be brought up with it, including naturally occurring radioactive material (NORM), asbestos, lead, and general hydrocarbons decontamination.

Mercury, one of those rare metals which becomes a liquid at ambient temperatures is, according to Jenkins, “a unique challenge”. It can contaminate any equipment, be it floating production and storage vessels, offshore production platforms, and pipelines, and each segment presents its own challenges, he said.

PEI typically begins the identification process with a non-destructive XRF pre-screening of test spools and samples to determine the surface loading and distribution. XRF analyzers use X-ray fluorescence to identify the elements contained in a surface-scale compositions and other sample materials. According to Jenkins, this method allows for instantaneous distribution, with the data translated to surface-mass loading distribution maps. In a recent PEI case study the operator wished to re-use the equipment. Where the plan is for complete decommissioning, the contractor can conduct additional verification through destructive testing in the form of an acid-digestion analysis and/or thermal-desorption analysis.

There are at least half a dozen options to choose from when it comes to removing mercury from hydrocarbon-processing systems, according to Jenkins. These include: chemical circulation; vapor phase chemical applications; various mechanical and robotic high-pressure jetting; vertical surface treatments which increase chemical contact times; sequential chemical treatments; and various mechanical and chemical pigging options. Chemistries are formulated to remove hydrocarbon and metals (mercury and arsenic) in a single phase based on certain mass-removal objectives determined during assessment.

Once decontamination is complete, the next task is to deal with the spent chemistries and minimize waste, Jenkins said. In a case study involving full-scale processing in which additives are mixed in ISO-standard tanks, PEI and partner ISCT processed 50,000 liters of extreme-pH spent chemistry and solids particulate, as well as 15,000 liters of mercury-containing rinsate. Residual unconsolidated sludge consisting of 10-20% solids was accumulated, along with particulate, and sent to a centrifugal decanter. Consolidated sludge consisting of 28%-50% solids was drummed and disposed as mercury-containing solids.

Throughout most of the world there are very few options for disposal of high-mercury containing fluids and solids which makes processing to discharge levels an attractive and economic solution, Jenkins said.

Mercury assessment should be included in decommissioning planning, he said, adding that data collection is of vital importance. “When you go to decommission that piping and equipment, you need to be able to tell the receiving party – the recycler – that it is mercury-free… You want to capture as much data as you can during the asset-life cycle, so that when you get to the end you know how much mercury you have.”

Dismantling before decontamination

PSC has conducted remediation and abatement for the offshore oil and gas industry since 1977, and the latest asset in its portfolio is a specially dedicated disassembly facility. In 2012 a major operator asked PSC if they could provide a decommissioning facility that could manage an abandonment program for offshore platforms with environmentally sensitive issues, potential for environmental impact, and potential to expose personnel to health risks, Wimberley recalled.

“At that time, no such facility existed,” he said, explaining that PSC found a suitable location on the Intracoastal waterway, and used an in-house engineering team to design and construct the facility. Offshore platforms are brought by barge to this facility. The largest platforms are cut into pieces over a 6,300-square foot concrete slab, “to make sure that there’s no decontamination spread in the area” and that there is no cross-contamination with equipment brought in from other projects, Wimberley said.

The facility is set up to conduct decommissioning of platforms, marine vessels, pipelines and living quarters, and is complemented by an adjacent decontamination facility.

Describing the advantage of having everything in one location, he said: “Instead of having mobilized crews or equipment offshore… if a client can button up the facility, cut away from the pipelines and just bring the whole facility right into the PSC receiving yard, we can handle all the decontamination, flushing, hydrocarbon removal all in one place, on a land-based operation where your crews are not having to mobilize back and forth. And we think it would save the client a considerable amount of money to do it this way.”