Abstract:
Naturally-occurring radionuclides deposited beneath the earth, which are referred to as "NORM" and other toxicnon-radioactive elements transported to the earth surface with the oil and gas production. Hence, knowledge of the prevailing background levels of these elements in the subsurface reservoir formations is valuable to all stakeholders, most notably to regulatory authorities of the country. The drill cuttings obtained within depth range 3025m to 3095m of reservoir sand section in the deep water exploratory well (CLPL- Dorado 91 H/1z) drilled in the Mannar Basin offshore Sri Lanka were subjected to high-resolution Gamma-ray spectrometry and X-ray fluorescence (XRF) spectrometry.
As test results revealed activity concentration of 40K varies from 0.338 Bq/g to 0.514 Bq/g, 210Pb from 0.007 Bq/g to 0.015 Bq/g, 226Ra from 0.012 Bq/g to 0.0145 Bq/g while 232Th levels are between 0.030 Bq/g to 0.040 Bq/g. According to the XRF testing levels of significantly hazardous non-radioactive elements are considerably lower, except for the level of the Barium. The Pb level varies between the 48 ppm to 22 ppm. The Thorium level varies between 9.6 ppm to 10.1 ppm. Manganese has a range of 5,173ppm to 653ppm.The barium levels are between 118,666 ppm to 24,400 ppm. NORM concentration of the tested section were on the lower side when results matched with the IAEA published data on NORM concentration in oil, gas and there byproducts and therefore there will be low level of NORM contaminations when the Dorado gas discovery proceeds to the production stage. Further there is no harmful public exposure from NORM by disposing these drill cuttings to environment or storing at any site location. But the disposal of the drilling mud and handling of the drilling mud should be conducted with cautious since extremely high Ba levels can potentially cause health problems.
