远距离井间电磁成像测井快速反演算法

Fast inversion method for long distance cross-well electromagnetic imaging logging system

远距离井间电磁成像方法可以实现500 m以上地层剖面成像,在资料反演中反演地层的精度以及速度是研究的重点和难点.本文提出利用格林函数方法取代差分近似方法计算雅克比矩阵的快速算法,通过与全空间差分近似法对比,验证了快速雅克比矩阵算法的正确性,格林函数方法极大地提高了反演成像效率;通过建立地质模型进行仿真,验证了格林函数方法求取雅克比矩阵的高斯牛顿反演算法完全可应用于远距离井间电磁成像,实现了对二维地层电参数以及边界位置的确定.反演速度是差分近似法的数十倍.

Long distance cross-well electromagnetic imaging method can explain the formation profile more than 500 m.The emphasis and difficulty of data processing focus on the accuracy and speed of inversion method.A fast inversion method is suggested as a substitute for difference approximated Jacob matrix calculation based on Green function.Then the method is verified by contrast with the result of difference approximation method.It improves the calculation speed significantly.The simulation results under formation model show that the Gauss-Newton inverse algorithm with modified Green function Jacob calculation applied in long distance cross-well electromagnetic imaging logging system is feasible for axial symmetry 2 D non-uniform formation.The parameters and bounders can be determined for 2 D formation.The speed is dozens of times faster than difference approximation method.