Evaluating Oil Potential in Shale Formations Using Terahertz Time-Domain Spectroscopy

Abstract

Optical assessment of oil shale using terahertz time-domain spectroscopy (THz-TDS) was carried out to study oil potential. Fischer assay testing was employed to obtain the oil yield of oil shale specimens to examine the difference of oil potential between oil shale samples from three regions: Beipiao, Barkol, and Huadian in China. Then, two types of specimens from each area were prepared for the optical tests and the results were compared. The refractive index (n) at 0.2–1.2 THz was derived; n decreased slowly with increasing frequency for all the specimens despite the oscillation pattern observed at lower frequencies. The specimen preparation method that mixed the powdered material led to minor differences between the specimens. The different response of kerogen to the terahertz pulse depending on the kerogen's evolutionary stage leads to a difference in the refractive index between the specimens from the various regions. This study indicates that using THz-TDS to evaluate the oil content in oil shale without inducing reaction within the specimen can be an effective method for resource exploration.

Simultaneous Determination of Organic Distribution and Content in Oil Shale by Terahertz Imaging

“…The average n values were 1.98 and 2.16 for the oil shale from Huadian and Beipiao, revealing an inverse relationship to the oil yield by the previous Fischer assay method. 23,24 After high-temperature pyrolysis, kerogen was completely decomposed. Thermogravimetric analysis (TGA) measurements were then performed by simultaneously heating and weighting both samples.…”

“…Fourier-transform infrared spectroscopy, Raman spectroscopy, mass spectrometry, and nuclear magnetic resonance were used to characterize the properties of oil shale. − Owing to the location between far-infrared and millimeter-wave spectrum bands, terahertz (THz) spectroscopy has recently emerged as an efficient tool in various aspects because of its unique advantages. − The response of a THz wave is strongly related with the materials’ dielectric properties . To date, THz technology has been utilized to evaluate the dielectric properties of various minerals and rocks, including kaolinite, montmorillonite, halloysite, sandstone, limestone, marble, etc., showing different quantitative relations between the mineral’s content and THz parameters. − In the study of oil shale, relations were built between THz absorption and the oil content in semicoke, which could be a significant indicator of pyrolysis process optimization. − The anisotropic optical responses of oil shales were measured by THz spectroscopy, revealing a refractive index ( n ) anisotropy associated with the bedding planes. Increasing organic content has promoted the anisotropic degree of oil shale, and a linear correlation can be built between the n anisotropy and the oil yield, providing an alternative parameter for oil yield characterization .…”

Mechanism of the Laser-Induced Voltage Generated in Oil Shale under the Irradiation of a 532 nm Laser

“…During the pyrolysis of oil shale, it is very important to analyze the dynamic characteristics of the organic evolution and oil production, which contributes to the understanding of the complex petrophysical changes in the hydrocarbon-recovery process. , With the development and comprehensive utilization of various advanced techniques, considerable information regarding the pyrolysis kinetics of kerogen and the oil-yielding potential of raw oil shale has been obtained by terahertz time domain spectroscopy (THz-TDS), laser ultrasonic technique, solid-state 13 C nuclear magnetic resonance (solid-state 13 C NMR), Fourier transform infrared spectroscopy (FTIR) spectroscopy combined with thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). − As a widely used means in material characterization, the laser-induced voltage (LIV) effects have been observed in various bulk materials and thin films, which is sensitive to their interior composition and structures. Based on this effect, the evaluation of oil and gas reservoirs has also been achieved .…”

Laser-induced voltage of shale due to photothermal effect

“…drilling depths, the environmental conditions have become challenging; thus, the development of oil and gas resources will become increasingly difficult. Lasers, which are insensitive to harsh physical environments, can serve as an appropriate method to promote the development of an unconventional oil and gas industry [6][7][8][9][10][11].…”