Naturally occurring radioactive materials in the gas and oil industry: origin, transport and deposition of stable lead and 210Pb from Dutch gas reservoirs

Abstract

The omnipresence of Naturally Occurring Radionuclides (NORs) within the Earth is well-known. Since long, radioactive decay of NORs has been recognised as the primary source of our internal planetary heat, and driving force of volcanism and the movement of plates forming the Earth's crust. Since NORs are most abundant in the Earth's crust, from which all oil and gas are produced, it is no surprise to encounter NORs in the oil and gas industry. Already at the beginning of the 20th Century, it became clear that NORs can be produced together with hydrocarbons. In oil and gas production facilities, enhanced quantities of some NORs can be found in the hydrocarbons themselves, in coproduced water, and in all kinds of waste materials such as mineral scales and sludges. Production water and deposits containing NORs have been termed NORM, i.e. Naturally Occurring Radioactive Materials, or TENORM, i.e. Technologically Enhanced NORM. The presence of NORM in production facilities can face oil and gas companies with large additional costs in maintenance, treatment and lost production, while extra care has to be taken regarding the environment and the health of production personnel. Therefore, management of NORM is essential to the oil and gas industry. Knowledge on the occurrence, origin and formation of NORM forms the basis of NORM management. Understanding NORM might assist in prediction or even prevention of NORM build-up in production facilities, leading to important risk and costs reductions. This study was initialised to gain insight into the chemical behaviour and physical properties of primordial NORs U and Th and their decay products in hydrocarbon reservoirs and production facilities during production, processing and treatment of oil and gas. More specifically, three topics were selected in order to establish the influence of geochemical and production parameters on NORs, from subsurface to production facilities: a) accumulation of NORs in hydrocarbon source rocks and reservoir rocks, b) transport of NORs together with produced liquids and gases into production lines, and c) build-up of NORM in facilities. Focus of this study was the encounter of 21°Pb in the production of natural gas from Dutch reservoirs.