孔隙地层中声波诱导的电磁场测井响应模拟

声电效应测井过程中,当充流体井中发射的声波传播至井外时,在孔隙地层中引起含带电离 子的孔隙流体相对于固体骨架流动,导致电磁场. 在忽略转换电磁场对声场影响的条件下,先采用Biot-Rosenbaum模型计算孔隙地层中的 声场,再计算声波诱导的电场和磁场. 计算结果表明,有伴随纵波波群和横波波群的电磁场、有伴随斯通利波的电磁场,还有微弱的 临界折射电磁波. 计算还表明: 接收器偏离井轴越远,电场和磁场的强度越大; 在井壁处,磁场强度的波形与轴向电场强度的波形相似.

Simulation of well-log response of the acoustically-induced electromagnetic field in a porous formation

During acousto-electric logging, the acoustic wave excited by a point acoustic source in a fluidfilled borehole propagates into the fluid-saturated porous medium and causes relative motion between the charge-bearing pore fluid and the skeleton, inducing electromagnetic field. To simulate the logging response, a numerical full-waveform simulation method is proposed. The acoustic field is taken as uninfluenced by the converted electromagnetic field, and is solved separately. The electric field is taken as quasi-steady. The full Biot-Rosenbaum model is adopted to obtain expressions for the acoustic field around the borehole. These expressions are then used to formulate the converted electric and magnetic fields in and out of the borehole. Calculations show there are electric and magnetic fields that accompany the compressional, the shear and the Stoneley waves. And there is a critically refracted electromagnetic wave, which travels along the borehole wall. The amplitude of this wave is very weak in the full waveform. Both the axial and the radial components of the electric field increase when the receiver is placed farther off the borehole axis. On the borehole wall, the shape of the waveform of magnetic field is similar to that of the axial electric field.