Mercury present in produced oil and gas will deposit onto the internal process infrastructure via a number of mechanisms including chemisorption and adsorption with the primary mechanism being through reaction with iron sulphide to form mercury sulphide. Due to the volumes of fluids produced and the length of time facilities are in production, even where the produced fluids have historically contained relatively low concentrations of mercury, pipeline scales containing percentage levels of mercury may be present.

Thus, aged facilities and infrastructure that have reached the end of their operational life and are selected for either recycling or abandonment, may pose a serious risk to health and the environment if the decommissioning process is not managed correctly. Smelting, hot cutting or other thermal/abrasive surface preparations for example, can lead to significant release of elemental mercury, a worker exposure hazard. Alternatively, if sub-sea pipelines are abandoned in-situ, all mercury present will ultimately be transferred to the local ecosystems. Consequently, the oil and gas industry have the requirement for a complete mercury decontamination solution from initial evaluation, demonstrable cleaning efficacy through to a guarantee for the treatment and disposal of the mercury waste generated in an environmentally-friendly manner.

In order to decide upon the most appropriate decontamination solution, an evaluation of the extent of mercury contamination should be undertaken. A novel approach that has recently been successfully implemented involved analysis of pipe sections by multiple analytical techniques, providing the mercury concentration in the scale/steel. From this, the total mass of mercury across the process or pipeline was approximated.

Subsequently, the efficacy of the preferred chemical to remove mercury from the internal surfaces of pipework was evaluated by chemical treatment of the pipe sections under laboratory conditions.

In-situ decontamination can be performed by a number of applications, including (i) the use of chemical pig trains in pipelines, (ii) closed loop circulation of chemical around topside process equipment and (iii) high pressure spraying of large surface areas such as storage tanks, FSO / FPSO vessels. The mercury waste generated is treated, on site or off site, to minimise the volume and disposed of in accordance with international regulations.

An all-encompassing mercury decontamination solution is described. Trials involving the chemical treatment of steel sections have demonstrated that more than 97% of the mercury deposited can be removed from the internal surfaces of pipelines and safely disposed of, significantly reducing the risk of (i) mercury release to the environment and (ii) worker exposure to mercury during smelting activities.

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