Radioactivity in Oil Exploration: A Radiological Concern or Not?

Introduction: One of the earliest mentions of radioactivity in oil was published in 1906, a mere eight years after the discovery of radioactivity by Henri Becquerel. Today there is some 95 million barrels of oil used every day with 22% of the consumption used by the United States. Some 45-50% of petroleum is used for transportation. While petroleum usage is declining due to competition of natural gas and more automobile efficiency, there is still a significant worldwide exploration and usage. In the 1980’s ²²⁶Ra began to be noticed when scrap metal dealers would detect unacceptably high levels of radiation from oil-field piping. Technologically Enhanced Natural Occurring Radioactive Material (TENORM) will develop in high concentrations in by-product oil and gas waste streams. The TENORM will chemically separate from other piped material in the process of the extraction of oil, resulting in high concentrations of ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb and other radioisotopes in a densely caked layer on the inner surfaces of the piping The activity of the ²²⁶Ra from TENORM ranges from 185 to several tens of thousands Bq/kg of sample. By comparison, the NORM concentration of radium in rock and soil is, at a natural level, 18.5-185 Bq/kg.

Methods and Results: Over the last six years we have investigated low level gamma-ray counting of ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb in oil scale in west Texas oil exploration. As well we used neutron activation analysis to determine barium and strontium at very high levels, giving credence that some of chemical compositions of radium existing as Ra with Ba and S Sulphates Along with these investigations we also showed that there is an underestimation of ²¹⁰Pb with its 46.5 kev photon due to serious self- attenuation. We recently used MCNP calculations to ascertain the dose to a hypothetical worker based on typical radioactivity levels of scale for ²²⁶Ra (2630 Bq/kg), ²²⁸Ra (1370 Bq/Kg) and ²¹⁰Pb (565 Bq/kg). Based on a phantom we calculated the dose to a multitude of organs in the body.

Conclusions: The major contributors of radioactivity in the oil field, soil, scale, and sludge were measured using gamma-ray spectroscopy. A human phantom was utilized to observe absorbed dose rates in various body parts, among which, skin was found to receive the highest dose rate. Further validation with in situ measurements is needed with dosimeters positioned in the modeled oil field to record radiation dosage. In particular it should be noted radiation levels as shown can significantly enhance yearly body dose rates. This work has demonstrated that MCNP provides a useful tool in terms of estimating radiation dose distribution in the human body in a complex radioactive environment such as the oil and gas industry.