Experimental Studies of Electrokinetic Conversions in a Fluid-saturated Porous Medium

The electrokinetic effect in a fluid-saturated porous rock is defined as the coupling and conversion between seismic and electric energies. When seismic waves propagate through a fluid-saturated formation and cause a pore fluid-flow relative to the solid matrix, the motion of the cations in the fluidflow forms a streaming electrical current and induces an electromagnetic wave at any discontinuous interface of the formation or stationary electric potential inside the homogeneous formation. Another conversion of energies opposite to the seismoelectric conversion is when an alternating electric field induces a relative fluid-flow in a fluid-saturated porous rock where fluid-flow can generate an electroseismic wave in the rock. In this paper we study the electrokinetics in porous sandstone and man-made porous models at high frequencies. A P-wave or S-wave transducer excites different acoustic wave modes in a cylinder, layer, or borehole model. Our experiments observe and record the radial or stationary seismoelectric signals induced at the interface or inside the formation. Some relative experiments have confirmed the reliability of the electrokinetic phenomenon observed in our experiments and the mechanism that is different from the piezoelectric effect. The results show that the seismoelectric signal induced by the extensional or flexural wave in the sandstone cylinder is a stationary local electric potential. The seismoelectric signal induced at the interface of the layer model is an electromagnetic wave which can be received within the fluid-filled porous medium. Experimental measurements performed in a borehole model by means of vertical seismic profiling (VSP) and single borehole logging show it is possible to conduct seismoelectric measurements in a deep borehole of petroleum formation. Measurements of electrokinetics can thus provide an effective means for estimating parameters in a fluid-saturated porous formation.