Terahertz spectral features and quantitative analysis of minerals in Ordos Basin Yanchang Formation
Abstract
The clastic sedimentary of Upper Triassic Yanchang Formation in the Ordos Basin is the typical reservoir of low permeability sandstone reservoir rocks. The accurate identification and quantitative analysis of rock components are the basis of reservoir evaluation. The optical properties and spectral features characteristics of the common mineral is studied using terahertz time-domain spectroscopy technology (THz-TDS). Through analyzing the absorption of the whole band, the paper chooses the sensitive spectrum ranges (0.1–1.7 THz) for sedimentary rock as the valid ranges in Yanchang Formation. Then on the basis of Fast Fourier transform, the optical parameters characteristics of each single mineral, such as time domain spectrum, frequency domain spectrum, absorption coefficient spectrum, refractive index spectrum, are analyzed.. The result shows that different minerals have distinct difference at the spectral features. Thus the content of single mineral in rocks can be analyzed using terahertz time-domain spectroscopy technology. Based on this point, the relationships of spectral features between sedimentary rocks and its main components are analyzed in Yanchang Formation. The results demonstrates that the terahertz spectral characteristics of sedimentary rocks and its main mineral components are appropriate for the law of Beer-Lambert. At the same time, they can also indicate that the terahertz characteristics of sedimentary rocks have close relationship with its components and also are the comprehensive reflection of its components. Therefore the author proposes the method of linear regression to predict the contents of rocks in Yanchang Formation with the terahertz spectroscopy of single minerals and sedimentary rocks.
