Determination of Low Concentration Impurities in Crude Oil By Nuclear Technique

An important challenge in the petroleum industry is to control and reduce the impurity content to acceptable levels in crude oil. Continuously monitoring the desired impurities such as salt and sulfur is thus an important direction of development. Nowadays, it is still regarded as a challenging assignment to develop an on-line and non-destructive measurement system which also has the feature of safe and reliable. In this work, two measurement systems based on neutron activation analysis (NAA) used for determining the concentration of impurities have been established. Two methods for non-intrusive and on-line monitoring of the impurity in the crude oil, especially for chlorine stand on delayed gamma-ray neutron activation analysis (DGNAA) and prompt gammaray neutron activation analysis (PGNAA) have been proposed and tested, named two-tank and PGNAA measurement systems, respectively. For the two-tank measurement system, it has been built in conjunction with a portable Pu-Be neutron source for measuring the delayed gamma-ray from radioisotope as long as possible until its activity reaching maximum equilibrium. The flow will keep recirculation continuously in closed circuit between two tanks, activation and detection tank. Simulations with various Monte Carlo N-Particle version (MCNP6, MCNP5 and MCNPX) and CINDER code package were utilized for building prediction model. The initial experimental results have been fitted by a mathematical model and benchmarked with simulated results. In the PGNAA measurement system, a portable pulsed neutron generator producing 14MeV neutrons in deuterium-tritium (DT) nuclear reactions has been under consideration. Simulation tools including MCNP6 in conjunction with Center for Engineering Applications of Radioisotopes Detector Response Function (CEARDRF) code and a specific purposeMonte Carlo code called Center for Engineering Applications of Radioisotopes Coincidence Prompt Gamma-Ray (CEARCPG) were used not only for the design optimization of the experiments but also generated elemental libraries spectra for library least-square fitting. Preliminary results indicate that a minimum detection limit for chlorine impurity of about 71 mg/L is achievable for an integration time of 30 minutes. In PGNAA on-line applications, theMonte Carlo Library Least-Squares (MCLLS) approach is one of the methods for quantitative analysis all elemental weight fractions via assuming that total gamma-ray spectrum is using linear combinations of contributions from the individual prompt gamma-ray spectra of the sample constituents. CEARCPG is utilized to generate the prompt gamma-ray libraries of each constituent. In this work, the focus was on detecting and measuring chlorine impurity in crude oil samples, i.e. trace amounts of chlorine. A preliminary study investigating the feasibility of PGNAA method in conjunction with the MCLLS approach for measuring trace amounts of chlorine in oil samples was performed. For this purpose, an extended version of the MCLLS approach, the so-called MCLLSX approach, was proposed and applied for the quantitative analysis. The analysis results presented in this work prove the feasibility of the proposed approach.