Spectroscopy studies on the Tuha crude oil in the terahertz range

Abstract

In this paper, the optical characteristics of crude oil samples from selected territories in Tuha oil field have been investigated with THz-TDS at room temperature in nitrogen environment. The absorption coefficient and refraction index of crude oil are calculated in the frequency range of 0.20~2.5 THz. No distinct absorption peak has been found in the spectra, which may result from the complexity of the constitution of the samples and the water content. The absorption coefficients increase with the content of wax in the samples with different slopes, which means the intensity of absorption in THz wave band increases with enhanced density of the sample and unaltered thickness. The average refractive indices were 0.62070, 0.59767 and 0.59290 corresponding to TuLuFan, ShanShan and WenMi territories, respectively. The refractive values show the phenomenon of abnormal dispersion, which meant the samples had the characters of strong selective absorption in this wave band. In contrast, we have also utilized Fourier transform infrared spectroscopy (FTIR) in the 400-4000cm-1 to measure the mid-IR absorption spectra, and the results revealed that the crude oil is more active in the range of Terahertz than in the mid-IR band. The experiments demonstrated that THz-TDS is a powerful tool to complement the conventional analytical approaches and can be applied to detect and analyze the features of the constituent in crude oil.