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

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.