Natural Occurring Radioactive Materials (NORM) in the oil and gas industry

Abstract

Radioactive materials which occur naturally and expose people to radiation occur widely, and are known by the acronym 'NORM'. Exposure to NORM is often increased by human activities, eg burning coal, making and using fertilisers, oil and gas production.

Many natural materials contain radioactive elements (radionuclides). The earth's crust is radioactive and constantly leaks radon gas into our atmosphere. However, while the level of individual exposure from all this is usually trivial, some issues arise regarding regulation, and also perspective in relation to what is classified as radioactive waste.The radionuclides identified in oil and gas streams belong to the decay chains of the naturally occurring primordial radionuclides 238U and 232Th. Analyses of NORM from many different oil and gas fields show that the solids found in the downhole and surface structures of oil and gas production facilities do not include 238U and 232Th. gas

These elements are not mobilized from the reservoir rock that contains the oil, gas and formation water.

Formation water contains the radium isotopes 226Ra from the 238U series, and 228Ra and 224Ra from the 232Th series. All three radium isotopes, but not their parents, thus appear in the water co-produced with the oil or gas. The 228Th radionuclide sometimes detected in aged sludge. This causes their precipitation as sulphate and carbonate scales. The mixed stream of oil, and water also carries the noble gas 222Rn that is generated in the reservoir rock through decay of 226Ra. It would appear that the concentrations of 226Ra, 228Ra and 224Ra in scales and sludge range from less than 0.1 Bq/g up to 15 000 Bq/g. Generally,

 the activity concentrations of radium isotopes are lower in sludge than in scales, the opposite applies to 210Pb. The deposition of contaminated scales and sludge in pipes and vessels may produce significant dose rates inside and outside these components. Maximum dose rates are usually in the range of up to a few microsieverts per hour. In exceptional cases, dose rates measured directly on the outside surfaces of production equipment have reached several hundred microsieverts per hour, which is about 1000 times greater than normal background values due to cosmic radiation and terrestrial radiation.