CSAMT全区电阻率法数值模拟及应用探讨

Numerical simulation and application discussion of the CSAMT Full-zone resistivity method

常规的可控源电磁法理论在计算视电阻率公式上,多半采用其电磁场的渐近特征,难以直接反映全区视电阻率的值,及直观地显现地下介质的地质构造.文中采用水平偶极子激发的电磁场,提出了电场的全区精确表达式,直接计算出大地电阻率.利用汉克尔数值滤波算法和逆样条插值算法对水平层状电磁场进行正演计算,并与计算的卡尼亚视电阻率的对比和野外试验结果表明:该方法的结果在远区等价卡尼亚电阻率,在近区和过渡带则明显地改善了卡尼亚电阻率的非波场区场崎变,从而能更好地接近基底的真电阻率,更形象地反映了地下介质的垂向电性变化.

The electromagnetic theory of conventional CSAMT mostly adopts its approximate characteristic in calculating the expression of the apparent resistivity. This method is difficult to reflect directly resistivity values at full-frequencies and show clearly geological structure in the subsurface. The paper presents a new full-zone expression of the electrical field to calculate directly and accurately earth resistivity by using the electromagnetic fields from horizontal electric dipole. Using Hankel digital filter algorithm and inverse spine interpolation algorithm to simulate electromagnetic fields of the horizontal layers , we contrast the calculational Cagniard apparent resistivity with its results and field experimentation. The results are equal to Cagniard resistivity in far-field , but in near-field area and transient area, the results have greatly improved the strong distortion of Cagniard resistivity. So the results can reach the true resistivity and indicate the changing features of conductivity of subsurface much better than Cagniard resistivity does.