Mercury management during decommissioning: predicting accumulation and mitigating risk of release

Abstract

In 2021, Australia ratified the Minamata Convention on mercury, an international treaty that seeks to protect human health and the environment from anthropogenic emissions and releases of mercury and mercury compounds. Mercury is a highly toxic metal with damaging effects even at extremely low concentrations. Decommissioning of pipelines and topside equipment that have processed fluids containing even trace quantities of mercury may create significant hazards to personnel and the environment. This paper considers the various mechanisms by which mercury accumulates in process systems and addresses important considerations, to mitigate the risks of mercury release during decommissioning. Where production fluids contain trace quantities of hydrogen sulfide, in addition to mercury, then mercury can react with compounds in scale layers to form mercury sulfide deposits, incorporated within the scale. In addition, mercury may also physically adsorb onto steel surfaces and within porous scale layers, and if mercury condensation occurs then amalgams may form with susceptible metals. Where pipelines are coated or clad, mercury can still be physically or chemically adsorbed onto the pipeline at weld joints. Production fluids containing mercury may also permeate through spiral-wound metal carcass layers of flexible flowlines. Mercury trapped in the carcass voids may be retained after flushing, to be released later during recovery operations, presenting a risk to personnel and the environment. Estimating the quantity, forms and areas contaminated with mercury compounds supports future decommissioning strategy development and select mitigation measures that reduce risks to personnel and the environment to as low as reasonably practicable.