| Summary: | 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 fluid- flow 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.
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