用改进的局域非线性迭代方法计算三维井间电磁场

COMPUTATION OF 3-D CROSS-WELL ELECTROMAGNETIC FIELDS WITH A MODIFIED LOCAL-NONLINEAR ITERATION

提出了用改进的局域非线性迭代 (MLNI)计算体积分方程的方法 ,并计算了三维井间电磁场。将井间大尺度电导率异常体分为近场区域和远场区域两部分 ,它们的位置和尺寸均随场点位置的变化而改变。对近场区域影响的计算采用局域非线性近似 ;将远场区域的影响作为外部激励源 ,采用迭代方法进行计算。由于不必进行直接的大型矩阵求逆运算 ,因而与体积分方程的直接解法相比 ,所需的机时更少 ,并减少了对内存的要求。数值计算结果显示 ,该方法也适用于高电导率对比地层 ,且计算精度与体积分方程直接解法的精度相当 ,是一种计算井间大尺度异常体散射场的有效方法。

A novel approach for volume integral equations with modified local nonlinear iteration (MLNI) is introduced. The 3 D cross well electromagnetic fields were computed using this method. The large scale scatters are divided into two parts of near region and far region, whose locations and sizes are decided by the point positions where electrical fields may be gained. The influence of the near region was worked out by the local nonlinear approximation method, while that of the far region was computed reiteratively, taking the far region as an external exciting source. The method requires less computation time and smaller memory than the direct computation of volume integral equations, since the large scale matrix inversion may be avoided. Numerical calculation indicates that the approach can be applied to high conductivity contrasted structures and has the same precision as the direct computation. MLNI method is an efficient approach for computing the scattering fields of large scale scatters.