鄂尔多斯盆地延长组矿物成分的太赫兹光谱研究

Terahertz spectral features and quantitative analysis of minerals in Ordos Basin Yanchang Formation

鄂尔多斯盆地上三叠统延长组碎屑岩沉积是典型低渗透砂岩储集层,岩石成分的准确鉴定和定量分析是储层评价的基础.应用太赫兹时域光谱技术研究了延长组常见单矿物在0.1–1.7 THz的光谱特征及光学参数特征,在傅里叶变换的基础上表明不同单矿物在太赫兹波段的光谱特征差异显著.利用太赫兹光谱技术可以分析岩石中单矿物的含量.在此基础上,分析了延长组沉积岩太赫兹光谱特征及其与主要组分光谱特征间的关系,研究表明沉积岩太赫兹光谱与主要组分光谱之间符合Beer-Lambert定律,沉积岩的太赫兹光谱特征是其各个组分光谱叠合的综合效应.因此,研究者提出了线性回归方法,利用岩石组分及沉积岩的太赫兹光谱预测了延长组岩石组分含量.

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.