Features of the Electric Response of Rocks to Vibration under Weak Nonuniform Fluid Saturation Conditions

Abstract

Abstract—The specific features of the electrical response of rocks to vibration in the 0.7–10 kHz frequency range were studied for Berea sandstone cores weakly and inhomogeneously saturated with polar and nonpolar fluids. Fluid was added to the samples with a pipette through a puncture in a protective film. In this case, a strong lateral saturation inhomogeneity was created at the lateral edge of the cylindrical core. During saturation, kerosene (as the nonpolar fluid) and saline aqueous solutions (as the polar fluid) were used in a volume of ~6% of the pore space. The physical modeling results showed that the electric response contains intense second harmonics, the amplitude of which at low frequencies is comparable to the amplitude of the first harmonics. When a 0.5% NaCl solution was added, a significant change in the electrical response in comparison to the response of the core in the initial state was observed only in the 5.45–7.15 kHz frequency range. When kerosene and a 0.05% saline solution was added to the core, an equally strong increase in the electrical response was observed at all frequencies; however, the nature of the spectral change and its temporal dynamics for polar and nonpolar fluids significantly differ. The presented physical modeling results will be useful for understanding seismoelectric processes in a heterogeneous, structurally inhomogeneous natural massif, and may also be the basis for new remote technologies to determine the type of rock saturation.