NORM Scale Subsurface reservoirs contain oil, gas and water in varying proportions. The reservoir is produced through an installation where the oil, gas and water are gravity separated within large vessels, known as separators, into three streams. The oil is exported via tanker or pipeline to an onshore reception terminal. The gas is exported via pipeline as well as being used for power generation on the installation. As a safety measure, excess gas is disposed of via flaring. The water (known as ‘produced water’), following appropriate treatment, may be disposed of by discharge to the marine environment, or by injection into suitable subsurface strata. Alternatively, the water may be re-injected into the hydrocarbon reservoir to maintain pressure and assist production. The water, having been in contact with various rock strata at elevated pressure and temperature, contains many soluble components including Barium and the radioactive intermediates of the Uranium and Thorium decay series. As the water is produced the temperature and pressure decreases creating conditions in which the Barium and radionuclides can co-precipitate inside separators, valves and pipework, forming an insoluble NORM (naturally-occurring radioactive material) scale. Some of the soluble radionuclides and particles of NORM scale will pass through the system and be discharged with the produced water. Similarly, some particulate scale and soluble radionuclides will be entrained with the exported oil and will be discharged from the onshore terminal. Fig 1 – Summary diagram of NORM Origins Sniffer (Scotland & Northern Ireland Forum for Environmental Research) 2005 Report UKRSR07 ‘Identification and Assessment of Alternative Disposal Options for Radioactive Oilfield Wastes (NORM Waste)’ NORM scale may significantly reduce the efficiency of the production equipment on an installation and must be periodically removed. Large fixed vessels, such as separators, can be opened and the scale removed using high pressure water jets. The removed scale is macerated to a particle size of 1mm or less and is then discharged to sea. Smaller items of plant, such as valves and pipework are transported ashore to be cleaned at an authorised facility prior to being refurbished and re-used. Scale arising from onshore cleaning is currently discharged to sea; however this practice is under review (see NORM Management Plan). Fig 2 – Heavily NORM Scaled Pipe Capacity has been reduced by 90% Sniffer (Scotland & Northern Ireland Forum For Environmental Research) 2005 Report UKRSR07 ‘Identification and Assessment of Alternative Disposal Options for Radioactive Oilfield Wastes (NORM Waste)’ Although certain parts of the produced water process system may be cleaned periodically, there is the potential for a quantity of NORM scale to remain within the system which must be dealt with at the time of decommissioning of the installation. Whether the NORM scale is cleaned and discharged offshore or at an onshore location will be installation specific and determined during development of the decommissioning plan. Fig 3- Main NORM Waste Streams from Oil and Gas Activities Sniffer (Scotland & Northern Ireland Forum For Environmental Research) 2005 Report UKRSR07 ‘Identification and Assessment of Alternative Disposal Options for Radioactive Oilfield Wastes (NORM Waste)’ NORM contaminated tubulars and plant material that are sent onshore for cleaning are currently only decontaminated at one site in Aberdeen; Scotoil Services Ltd. Historically, Scotoil has removed the scale from equipment, ground it into small particles, and discharged it via pipeline to the sea. Due to various reasons, SEPA has ruled that Scotoil may no longer discharge macerated scale to the nearshore marine environment from December 2008. Clearly, this places the oil and gas industry at risk as it effectively removes our onshore NORM scale disposal route. In August 2006, representatives of the Oil & Gas UK directorate and its members met to discuss the issue. As a result of these meetings, the Oil & Gas UK NORM Scale Management Plan was created to facilitate the search for sustainable disposal routes for NORM scale waste. Currently, work is in hand to identify interim storage options for NORM scale. NORM Scale Management Plan

Environment Index

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