低频交变压差作用下岩心流动电流和zeta电势实验测量

Experimental measurements on streaming current and zeta-potential of core samples under the excitation of low-frequency sinusoidal pressure

实验测量岩样zeta电势,对于认识地震诱导的电磁场现象以及探索利用动电效应的测井方法具有重要意义.本文介绍了专门设计的岩样流动电流和流动电势实验测量系统及一种获得岩样zeta电势的测量方法——流动电势和流动电流综合测量法.实验采用交流锁相放大技术,测量了3～100 Hz频率范围内交变压差作用下岩样的流动电势系数和流动电流系数,实验表明,这两个系数均随溶液浓度增大而减小,随pH值增大而增大.实验通过对不同浓度饱和岩样的流动电势和流动电流测量,获得了岩样的有效面积-长度比,进而计算出岩样的zeta电势和表面电导.实验还论证了忽略表面电导是导致常规流动电势测量法获得zeta电势低于实际值的原因.

The experimental measurements on zeta potential are important for the study of the electrokinetic phenomena during an earthquake and of the electrokinetic well logging methods.An experimental test system is devised to measure the rock streaming potential and streaming current. By employing the AC lock-in technique, the streaming potential coefficient and streaming current coefficient are experimentally obtained at the low frequency range between 3 and 100 Hz. The experimental results show that both coefficients decrease as the ion concentration increases, and grow as the solution pH value increases. By combining the streaming potential and streaming current measurements at different concentrations, the effective surface-to-length ratio of a core sample is obtained, which is used to calculate the zeta-potential and the surface conduction.The results also demonstrate that the neglect of surface conduction as in the conventional streaming potential method leads to underestimation of the zeta potential at the low concentrations.