SH-TE Seismoelectric Logging In Cylindrical Layered Porous Formation

The problem of seismoelectric in fluid saturated porous media has been one of the hot topics in geophysics.Based on this effect,seismoelectric logging technology is proposed.Due to fluid coupling,it is impossible to excite the SH wave in the porous media continuously in the borehole,so few people consider shear wave logging in recent years.In fact,Shear wave and P-SV wave are decoupled in the horizontal layered medium.So the SH wave propagation in parallel with the polarization direction of the interface does not produce the converted wave.If the SH wave can be utilized,it will be very convenient.In 1994,White conceived the use of horizontal sound sources close to the borehole wall to excite the SH wave,and carried out a preliminary theoretical solution to the homogeneous formation outside the well.It is shown that the direct exploration of shear wave is possible.In this paper,the theoretical simulation of the SH-TE seismoelectric logging in the borehole surrounded by a cylindrical two-layer porous medium is presented.In this paper,we study the seismoelectric logging in cylindrical layered porous formation.The interior of the well is fluid,and the annular porous interlayer is connected with the borehole wall,and then the outermost layer of the medium is an infinite saturated porous formation.This model can not only simulate the formation of the invaded zone,but also use the model to survey interface response.For SH-TE logging,based on Biot theory and Pride theory,and then through the introduction of potential function and using the method of Homheltz-type wave equations,we can solve the general equation of electromagnetic fields in the borehole in the absence of current source,and solve coupled seismoelectric wave field outside the well.In this paper,the expressions of the wave fields inside and outside the well are analyzed under the condition that the acoustic field is not affected by the converted EM field.Through the numerical simulation and the theoretical analysis,we can get two kinds of waveforms,and they are the SH wave and Love wave in the full wave acoustic field.We can also observe the two electromagnetic fields and the accompanying electromagnetic fields in the full wave electromagnetic field.The results show that although the influence of the well radius and the thickness of the interlayer on the acoustic field is complex,the influence on the interface response is not obvious.When the radius of the well increases,the accompanying electric field of the love wave decreases.The change of the fluid salinity in the borehole has no obvious influence on the acoustic field and electric field.The influence of the change of the fluid salinity of the interlayer on the acoustic field is very small,but the influence of the external interface response is obvious.The more different of two layers,the more obvious response of interface.The same is true for the outermost porous media.With the increase of the porosity of the interlayer,the velocity of SH wave and Love wave increases,and the amplitude will become smaller.The amplitude of the electromagnetic wave which generated by the inner interface is also increased.For the response of the outermost interface,the more different of two layers,the more obvious response of interface.The same is true for the outermost porous media.However,the porosity of the outermost porous media has no obvious influence on the acoustic field.The effect of the varying tortuosity of the two layers of the porous media on the acoustic field is not obvious,but for the electric field,with the increase of the tortuosity,the outermost interface response is more obvious.Through the investigation for the SH-TE seismoelectric logging,it can be obtained that we can use the characteristic of the first arrival of the radiated electromagnetic waves to the receiver to detect the interface which have large differences in the formation.