This paper describe. the deposition of naturally occurring radioactive materials (NORM) in oil and gas production facilities. Hazard. arising from process. maintenance and cleaning operations are process. maintenance and cleaning operations are considered and relevant legislation is detailed.
Potential doses to personnel are estimated and Potential doses to personnel are estimated and compared with actual doses received. Measures to reduce hazard to the workforce and general population are discussed. population are discussed
The presence of natural radionuclides in product materials from oil and gas reservoirs gives rise to deposits with enhanced levels of these radionuclides in processing equipment. Processing of the product fluids may also lead to increased levels in process streams.
These enhanced levels in deposits and products potentially pose a serious problem to operating, potentially pose a serious problem to operating, maintenance and cleaning personnel due to internal and external radiation levels on process equipment and the possibility of ingestion or inhalation of radioactive species. Additionally the distribution or disposal of contaminated items of equipment must be carefully controlled to avoid adverse effects on the general public and environment.
This paper demonstrates that by taking sensible precautions during production, cleaning and precautions during production, cleaning and disposal, potential doses to personnel may be reduced to acceptable levels.
The radioactive decay of Uranium-238 and Thorium 232, present in formation waters, produce other radioactive daughter elements. Figure 1 and Figure 2. Both decay series contain isotopes of radium, Ra-226 in the U chain and Ra-228 and Ra-224 in the Th chain. Although present in solution in extremely small amounts, because of the similar chemistry of the Group Th elements, Ra is incorporated in the simple or complex salts of calcium, barium and strontium forming part of the scales and deposits found in oil and gas production facilities.
The Ra-226 and Ra-224 sub-chains both produce radioactive isotopes of the noble gas radon, Rn-222 and Rn-220 with half lives of 3.8 days and 56 seconds respectively.
Although the major hazard associated with deposits undoubtedly arises from Ra deposition and decay, small quantities of U and Th isotopes have also been identified. These rarely amount to more than one percent of Ra concentrations and for the purposes of radiological protection may be purposes of radiological protection may be ignored.
The decay of all radionuclides in the U-238 and Th-232 chains take place by emission of either alpha or beta particles generally, accompanied by the emission of gamma rays. It is the impingement of these ionising radiations and the deposition of their energy which causes damage to the body tissues.