Determination of oil reservoir radiotracer (S14CN−) in a single step using a plastic scintillator extractive resin

Abstract

The analysis of radiotracers is important in the study of oil reservoir dynamics. One of the most widely used radiotracer is S14CN−. Prior to activity measurements by Liquid Scintillation (LS), routine determinations require the pretreatment steps of purification and concentration of the samples using anion exchange columns. The final elution media produces samples with high salt concentration that may lead to problems with phase separation during the LS measurement. Plastic Scintillation (PS) is an alternative technique that provides a solid surface that can be used as a platform for the immobilisation of selective extractants to obtain a PS resin. The proposed procedure unifies chemical separation and sample measurement preparation in a single step, serving to reduce the number of reagents needed and manpower required for the analysis while also avoiding mixed waste production by LS.The objective of this study is to develop a PS resin for the determination of 14C-labelled thiocyanate radiotracer in water samples.For this purpose, the immobilisation procedure was optimised, including optimisation of the proportion of PS microspheres:extractant and the use of a control blank to monitor the PS resin immobilisation process. The breakthrough volume was studied and the detection and quantification limits for 100mL of sample were determined to be 0.08BqL−1 and 0.31BqL−1, respectively. The established procedure was applied to active samples from oil reservoirs and errors lower than 5% in the sample determinations were obtained.