2.7.2.2 - Rn in Crude Oil and Oil Fractions

Introduction

Radon is easily extracted into organic solutions. This includes as well crude oil and oil fractions from the mineral oil industry. We have shown [Möbius et al. 2007, 2008, 2009] that LS presents a simple and effective analytical tool for the determination of Radon and other NORM nuclides. Radon (²²²Rn) in oil fractions has been measured in organic BetaPlate cocktail as 0.1 % solution for crude oil and up to 7% for yellowish mineral oils. An increasing concentration of oil in the organic cocktail results in a yellowish to brown color, shifting the energy spectrum to lower values. This effect is, however, highly dependend on the colour of the crude oil. They vary significantly from pale yellow to dark black and the intensity of this effect needs to be evaluated for each single measurement. An alternate is the measurement of the high energy β-emitting daughter nuclides ²¹⁴Pb and ²¹⁴Bi by the Cerenkov TDCR option.

Materials and Equipment

• PSD LS counter

• Organic cocktail

Procedure

1. 19 mL organic cocktail and 1 mL oil sample are mixed in a 20 mL LS vial (0.1 mL for black crude oil).

2. Measurement is done using the α/β-PSD option until the appropriate standard deviation is reached in the α-channel.

Evaluation

As only Radon is extracted into organic oil phases, virtually no other radionuclides can interfere. The counts in the α-channel result from ²²²Rn in equilibrium with its direct successors (²¹⁸Po, ²¹⁴Pb, ²¹⁴Bi, ²¹⁴Po). Thus, a counting efficiency of 300 % (3 x a) has to be taken into consideration for the calculation of the ²²²Rn activity (for details see chapter 2.2.1.2.).

Detection limits MDA depend on batch and have been measured down to sensitivities of 5 Bq/L due to the low α-background when using α/β-PSD in organic phases. With 40 Bq/L, the method is sensitive enough even for black crude oil samples.

Möbius R., Bartenbach M. and Veguera S. 2007: Problematik der natürlich vorkommenden Radionuklide (NORM) in der Erdöl/-gasindustrie und deren Bestimmung mittels Flüssigszintillationsmesstechnik; Proceedings LSC-Anwendertreffen, Karlsruhe 2007

Moebius S., Moebius R., Bartenbach M. and Ramamonjisoa T. 2008: Liquid Scintillation for NORM in the oil and gas industry; Paper, Proceedings IRPA12, Buenos Aires 2008

Moebius R., Bartenbach M. and Moebius S. 2009: Novel LS methods for natural radionuclides in the oil and gas industry; in: J. Eikenberg et al. “LSC 2008 Advances in Liquid Scintillation Spectrometry”, pp 397-407, Radiocarbon 2009, Tucson