The source and risks of mercury offshore

Mercury and heavy metals entrained with oil and gas production flows, particularly from older wells, can accumulate in pipes and process vessels, introducing a health hazard

Almost all oil and gas is found within the tiny spaces in sedimentary rocks, mainly sandstone and coarse-grained limestone.

Bedrock limestone and sandstone, even though hard, also contains lots of pores that can contain water or oil or gas and other elements.

Along with the gas and oil is a mixture of sand, silt and mud.

This sludgy silt mud is rich in heavier metal elements, including Uranium and Mercury.

Even the heavy Uranium can be suspended in the product as it is drawn from the well.

However because Mercury exists naturally in vapour form it is readily drawn along with the gas product.

Where these contaminants end up in the plant depends on many factors.

Mercury as suspended vapour in the product will act in the same way as many other oil and gas products.

During fractional distillation, temperature and pressure changes allow vapours to condense into selected by-products.

In the same way, certain vessels on the rig or in the refinery may lend the right conditions for vaporised Mercury to condense back into the normal liquid state.

Here it will form as either small globules or in small puddles, when collected naturally at the base of pipes and vessels.

In the case of the heavier elements suspended in the product, over time these form scale that can be egg shell-like or brown or grey to whitish slate-like layers or even layered variations like tree rings.

These deposits are formed of various elements, and may contain heavy metals from Uranium ores, through to Mercury.

THE RISKS OF MERCURY WHEN BREAKING CONTAINMENT.

It is expected that the heavier elements from the sludge will be drawn up increasingly when product is drawn from older wells.

These contaminants will include the heavier metals like Uranium and Mercury.

Recently on offshore installations, when breaking containment in vessels, engineers have found deposits and small puddles of liquid mercury.

Mercury will evaporate and can produce vapours harmful to operators at relatively low temperatures.

When a pressurised vessel that contains mercury droplets is de-pressurised, these vapours will start to be released.

When breaking confinement, even though a thorough gas test has proved there is no flammable gas present, the vessel could still present a hazardous health risk from invisible mercury vapours.

Able have provided portable Mercury analysers to determine the amount of Mercury vapour in such offshore tanks and containments: for further information on these detectors please consult the Able website or call the sales office.

Back to top