部分饱和岩样中震电响应的实验测量研究

Fluid-containing porous media induce an elastic-electromagnetic coupling effect (Seismoelectric effect) due to the presence of the double electric layer. This effect produces a converted wavefield that combines the spatial resolution of elastic waves with the electrochemical sensitivity of electromagnetic waves, thus attracts widespread attention in the geophysical field. However, most of the current theoretical simulations and experimental measurements of the seismoelectric effect are based on a single-fluid saturation model, which is inconsistent with the actual complex stratigraphic situation where multiple fluids are saturated. Therefore, we focus on the seismoelectric response of partially saturated condition and analyze the seismoelectric wavefields inside the rock sample in the laboratory. According to the gradual distribution of underground fluid saturation, we design a kind of experimental model that can realize the partial fluid saturation, then conduct experimental measurements of the coseismic waves and the interfacial electromagnetic waves inside the rock through the embedded electrodes. After recording the time-domain waveforms of these two converted wavefields, we discuss their propagation characteristics under the condition of partial saturation, analyze their amplitude attenuation laws, and compare their sensitivity to differences in saturation, so as to study the effect of saturated interfaces on the seismoelectric coupled wavefields. The experimental results show that the direct coseismic longitudinal wave, the reflected seismoelectric waves on the upper surface of the rock and the interfacial electromagnetic waves excited by the saturation interface can be observed inside the rock sample, and their amplitude attenuation matches the pattern of exponential law. The amplitude and velocity of the coseismic longitudinal waves are less sensitive to the saturation, but there are significant amplitude differences of interfacial electromagnetic waves in the rock with different saturations. Therefore, the seismoelectric conversion signals can be used to identify the saturation interface in complex reservoirs, which provides an important reference for the oil and gas localization and the reserve determination.