Study On Propagation Characteristics Of Seismoelectric Waves In Water-saturated Porous Media

The seismoelectric exploration technology has aroused considerable concern of scholars in the fields of logging and exploration, and the seismoelectric effect has become a leading subject in the field of geophysical logging. Now the studies and other related technologies have made great progresses, however, due to the lack of acknowledgement to microcosmic mechanism, people have not yet form a set of recognized, theoretical and mathematical methods by now. In this paper, the mathematical simulation on electromagnetic properties of seismoelectric waves was carried out by Pride’s theory. The mathematical simulation on electromagnetic properties of seismoelectric waves was made. Then, the influence of concentration polarization and DC electric field on seismoelectric effect in reservoir rock was analyzed.At the beginning, a mathematical model to describe seismoelectric effect was established in the water-saturated porous media, based on the coupling theory of the flow field and the electrical current field in capillary tube model. The comparisons on velocity, attenuation constant, electric field, electric current density and charge density of different kinds of waves were made; At the same time, the electromagnetic frequency responses on porosity and electrochemical properties were analyzed. The result showed that the velocity, attenuation constant and modulus of electric current density enhance with the increasing of frequency. For the same frequency, the fast longitudinal-wave has the fastest velocity and least attenuation constant, while the slow longitudinal-wave is contrary; The seismoelectric slow longitudinalwave has biggest modulus of electric field and transverse wave comes second. For the changes of porosity, these waves have different responses. With the increasing of the concentration or the decreasing of the cation exchange capacity, the modulus of electric field and electric current density decrease, their phases remain unchanged. The concentration and the cation exchange capacity have little effect on velocity and attenuation constant.Then, the seismoelectric coupled equations which consider concentration polarization is established, and the influence of the concentration polarization, the cation exchange capacity and porosity on the propagating of seismoelectric waves are analyzed by mathematical simulation. The result showed that for three kind of seismoelectric wave, the modulus of electric field decreases with the increasing concentration difference or the decreasing cation exchange capacity. For the transverse and fast longitudinal-wave, the modulus of electric field increases with the increasing porosity; while the slow longitudinal-wave is contrary. The direction of concentration difference always affects the electric field. The electric field in which directions of solid-phase vibration and concentration difference are mutually perpendicular is less than that in which directions are mutually parallel.Finally, based on the fact that DC electric field can change porosity, a mathematical relation of DC electric field and seismoelectric effect were established to explain microcosmic mechanism. The result showed that DC electric field can enhance seepage velocity and electric field strengths of the transverse wave and fast longitudinal-wave; With the increasing DC electric field and distance from the cathode, seepage velocity and electric field strengths of the transverse and fast longitudinal-wave become larger, while the slow longitudinal-wave has the contrary. At the same time, the degree of DC electric field enhancing seepage velocity and electric field strengths of the transverse wave and fast longitudinal-wave and the degree of DC electric field weakening seepage velocity and electric field strengths of the slow longitudinal-wave become smaller, when the porosity, concentration and cation exchange capacity increase.