Radiological impact assessment of produced water from oilfield production facilities in the Niger Delta region

Abstract

The concentration of radionuclides in produced water can vary significantly depending on the geological formations and the extraction techniques deployed in the production of oil and gas resources. Several factors such as water-rock interactions, reservoir age, and flow rates influence the mobility and concentration of radionuclides. High concentrations of radionuclides in produced water can pose potential risks to human health and the environment. This study combines laboratory measurements using Gamma Spectrometry and numerical modelling techniques to assess the concentration, and radiological impact of radionuclide exposure in samples of produced water collected from oil and gas production facilities. The mean activity concentrations of ²³⁸U and ²³²Th were 1.09 ± 0.17 Bq/l and 5.53 ± 0.36 Bq/l, respectively, while ⁴⁰K was negligible. The radium equivalent activity (Ra_eq) in the produced water samples ranged from 1.53 Bq/l to 7.47 Bq/l, indicating a relatively low radiological hazard. This low radiological hazard was corroborated by the findings of the annual effective dose equivalent (AEDE) and other impact parameters. The Th/U ratios for the samples ranged from 3.00 to 40.30, suggesting varying levels of uranium and thorium content in the produced water samples. The significantly higher Th/U ratio in sample B suggests the presence of specific geological conditions favoring thorium retention, which may have radiological implications, particularly regarding radon gas emissions and associated health risks in confined spaces. The presence of ²²⁶Ra in location B indicates geological leaching, while the variations in ²³²Th and ²³⁸U concentrations reflect differences in local geology and hydrogeochemical processes. The absence of detectable ⁴⁰K activity implies that potassium-rich mineral sources have limited influence on the produced water chemistry, although further analysis is needed to assess Potassium's overall geochemical contribution. These findings emphasize the need for continued monitoring and detailed geochemical assessments to better understand radionuclide mobility, potential contamination pathways, and their long-term environmental impact.