Seismoeletric Wavefields In Cylindrical Double Layered Porous Formation

Seismoelectric effect of porous media in the field of geophysical exploration has been the hot spot of attention, Seismoelectric effect effect, it is well known in electrochemical interface has the internal structure of electric double layer,it can cause two different types of electromagnetic field. One is with the electric field in the region of the sound wave disturbance, "With" here is relative to the sound waves. The other is a radiation(or spread) of electromagnetic fields, call interface of electromagnetic field, it was created in interface parameters characteristic of different media. The strength of the vibration signal and decomposition of surface vibration excitation intensity, the interface and the distance between the receiver and physical properties of the interface itself(elastic and electric property).This paper mainly studies the well is radial stratification of the two kinds of porous media. In the borehole fluid and unlimited extension of the outer a ring porosity sandwich between porous media, This model is designed to simulate have invaded zone formation. On the other hand, simulation studies can be carried out the interface detection. In this paper, based on the Biot theory, electric double layer structure, starting from the theory of Pride, through to the electric field vector and displacement vector helmholtz decomposition, and transformed Pride equation into wave equations about the potential function. Based on elastic wave, electromagnetic wave equations, Export the axisymmetric acoustic passive uniform pore medium electric coupling the explicit expressions of the wave, then, Export when stimulates in the Wells of noise source acoustic borehole acoustic field and electromagnetic field calculation formula, Further deduce the formation of coupled acoustic field and the expression of electromagnetic field.Using Fortran platform, independent compiler and to simulate, Got a conclusion: the full waveforms of the borehole fluid-pressure is dominated by the Stoneley waves there are the stationary electric field in the axial direction accompanying acoustic waves groups, meanwhile, also one can observes that there are three waves groups arrived earlier than the conversion electric field of the formation elastic wave, and almost simultaneously arrived at the different receivers. Influences of salinity on the interface response, salinity is inconsistent on either side of the interface, the interface response is obvious, on the full wave shape can’t see the interface response signal when the borehole salinity than hours in porous media; In the thickness of the porous medium layer interface response basic without what effect; When the well radius reduced hours, the range of the Within the interface of electromagnetic wave, even bigger than the fast p-wave amplitude. Waveform components become easy, Shear wave conversion electric field almost disappear. When can tell from the receiving sound pressure curve compressional wave, shear wave and stoneley wave, Transformation of electromagnetic field can also distinguish the corresponding wave packet. Electroacoustic ratio of p-wave is than most, The second stoneley wave is second, Shear wave than the smallest; When the larger porosity, the greater the electromagnetic field amplitude, The smaller the sound field amplitude. And porosity of porous medium change will impact on acoustic velocity; When the greater curvature, Sound field amplitude, The smaller the amplitude of electromagnetic field. The influence of curvature on interface of electromagnetic wave is not very big; Salinity change does not affect the sound wave is basically, but is more sensitive to convert electromagnetic field, Increase the borehole fluid salinity can increase the size of the electric field intensity; Increase the salinity of pore medium can reduce the size of the electric field intensity; Change the outer physical parameters of media, the sound pressure and the influence of electromagnetic field is not very big, but for the related interface The outside surface electromagnetic wave effect is more noticeable.