Optical and dielectric properties of water-bearing sandstones in the terahertz range

Water content significantly impacts the physical properties of sandstone. Studying the properties of water-bearing sandstone helps understand its behavior in seismic wave propagation, groundwater flow, and hydrocarbon reservoirs. This paper investigates the optical and dielectric properties of water-bearing quartz sandstone and arkose using terahertz time-domain spectroscopy (THz-TDS). The intrinsic dielectric permittivities were extracted using effective medium theory and fitted with the Debye model. Results show that increasing water content extends the slow relaxation time from 2.746 ps to 3.791 ps and the fast relaxation time from 0.032 ps to 0.282 ps. Compared to quartz sandstone, arkose shows a slower increase in dielectric permittivity due to restricted water molecule movement caused by its higher ion content, with the analysis focusing on the frequency dependence of the polarizability of the internal components.