RIASSUNTO
Abstract
Waste of Naturally Occurring Radioactive Materials (NORM) poses a challenge to operators and authorities alike.
The paper reviews legislation and practices regarding NORM waste management in the North Sea countries, with emphasis on the potential environmental impacts. The paper gives an overview of mechanisms causing NORM in the oil and gas industry, the various disposal methods, the legal regime, and the fate and effects in the external environment. Examples of current and future NORM waste challenges are given.
NORM in produced water mainly consists of Ra-226 and Ra-228, which has been dissolved from the geological materials of the reservoir. Parts of the dissolved Ra precipitate as RaSO4 in the process equipment onboard the installation (mainly in the separation systems), associated with precipitation of BaSO4 and SrSO4. If discharged to the sea, the vast majority of the dissolved Ra precipitates as RaSO4 or adsorbs to fine-grained particles and particulate organic matter. When assessing the fate and effects of NORM in the external environment, it is therefore essential to analyse both the fine-grained sediment transport pathways and the uptake mechanisms of marine life.
The strong particle-association of Ra must be taken into account when evaluating the possible environmental impacts of solid NORM waste disposal (from maintenance of equipment, decommissioning of installations, etc.). Re-injection of NORM back to the geological reservoir can be seen as an optimal way of disposing NORM waste, but the approach taken by different countries varies, depending on how the London Convention and the OSPAR Radioactive Substances Strategy are interpreted and implemented.
It is concluded that the NORM waste issue is not in all cases handled optimally with respect to health, safety and environmental impacts, partly because of the constellation of international conventions and national practices which is applied with significant variation from country to country.
Introduction
Concerns about health, safety and environmental (HSE) impacts of NORM (Naturally Occurring Radioactive Material) in the oil and gas industry were initially recognized in the 1970s and 1980s (Smith, 2010). Also in the Middle East NORM is a wellknown issue in oil and gas production (e.g. Bird et al., 2002, Al-Masri & Suma, 2003, Abdullah et al., 2008).
Due to the HSE risks, special precautions are required when handling NORM. NORM waste is primarily produced when radioactive substances present in the produced water (originating from dissolution of elements from the source and/or the reservoir rock) precipitates in vessels and pipings in the oil and gas treatment equipment, in particular in the water treatment system. This precipitated scale, sludge and deposited sand then arises as waste when carrying out maintenance of the equipment. Likewise, when offshore installations are decommissioned, NORM waste often occurs in significant amounts. The radioactivity of NORM is usually rather low, but the half-life of the radioactive isotopes of the NORM can be rather long (e.g. the half-life of Ra-226 is 1600 years).
No general consensus exists on how to best manage NORM waste from an environmental point of view. Different approaches to managing the NORM waste issue has been taken by different countries, even between countries with similar oil and gas production environments (e.g the North Sea countries). The origin of these approaches is often based on local perception of the risks connected to radioactive substances, on local interpretation of the international conventions etc.