Terahertz spectroscopy properties of trace crude oil in quartz sand

The purpose of this article is to classify the types of crude oils from different regions and oil-quartz sand mixture with different oil content with terahertz time-domain spectroscopy (THz-TDS). Multivariate statistical methods, including cluster analysis (CA) and principal component analysis (PCA), are used to build models between THz parameters and crude oils from different regions. The sample absorbance first increases and then decreases with the increase of oil content, revealing that the THz response is caused by the cracks and oil content simultaneously. When the oil content is smaller than the critical concentration, the existence of cracks makes more scattering; meanwhile, the more the oil content is , the larger the THz absorption becomes when the oil content is larger than the critical concentration. Consequently, the combination of THz technology as well as multivariate statistical methods could be an effective method for rapid identification of crude oils content and the geographical locations of crude oils.