NORM in Oilfield

Uranium (U) and thorium (Th), two radioactive elements, occur in oil and gas bearing

sedimentary rocks. Through radioactive decay over time, these two elements produce other

radioactive materials that emit ionizing radiation, known as daughter products. As oil and gas

transports to the surface, some of these radioactive daughter products, such as Radium (Ra), can

follow the oil and gas streams through the processing plant. NORM scale can form when

chemical, temperature or pressure differences occur. For example, when seawater is injected to

boost oil recovery, the high sulphate concentrations in the seawater combine with high Barium

(Ba), Strontium (Sr), or Calcium (Ca) ions in the formation water and cause precipitation of hard

scales. Since radium is chemically similar to barium, radium is incorporated into the scale

deposit.

In addition, produced natural gas sometimes contains Radon (Rn). The daughters of radon are

alpha and beta emitters such as Polonium (Po) and Bismuth (Bi) isotopes which can form thin

films on the inner surface of oil and gas processing equipment. During radioactive decay,

radiation can be present as alpha and beta particles or as gamma radiation. Each type of radiation

differs in its penetrating power. An outer layer of skin or a piece of paper can stop alpha particles;

a sheet of plastic or metal can stop beta particles. Gamma radiation requires shielding (thicker and

denser material is better, lead is commonly used) to reduce intensity to minimize impact on the

human body.

Only a small percentage of oil and gas facilities have NORM present in significant levels.

Measurements for gamma radiation taken on the exterior of operating oil and gas processing

equipment are usually well below allowable exposure limits. However, personnel exposure toalpha and beta radiation—via the pathways of inhalation, ingestion, or skin exposure to un-fixed

(particulate) NORM—can occur when opening equipment for inspection or repair.