定源回线TEM数据的约束反演方法及应用效果

Constrained inversion method and application effect of TEM data of fixed source loop device

为消除TEM定源回线装置增大接收区域后明显的边框效应,且提高TEM的分层能力,达到提高对不同电性地层精细分辨的目的,采用带约束的正则化反演方法。在反演算法中,拉格朗日因子采用CMD正则化因子的自适应调节方案,自主调整。为保证反演过程的高效、稳定且结果收敛性,使反演模型每一层的厚度按照等对数间隔进行离散,减少矩阵方程的病态性;同时对反演电阻率值采用可行的上下限约束,使迭代的结果不至于出现极值或错值,降低反演的多解性。通过对多层理论模型的计算,证明了约束反演算法的正确性和可靠性,将其用于实测瞬变电磁法勘探数据的反演计算中,反演电阻率纵向分布规律与已知地层电性资料吻合,解释的异常区得到了钻探验证,结果可靠。

In order to eliminate the obvious framing effect after the TEM fixed source loop device increases the receiving area,to improve the delamination ability of TEM to enhance the fine resolution for different electrical strata,the regularization inversion method with constraint is adopted.In the inversion algorithm,the Lagrange factor is adjusted adaptively by CMD regularization factor.In order to ensure the efficiency,stability and convergence of the results of the inversion process,the thickness of each layer of the inversion model is discretized according to the equal logarithmic interval,and the ill conditioned property of the matrix equation is reduced.At the same time,a feasible upper and lower limit is used for the inversion of the resistivity value,so that the extreme value or the error value can not appear in the results of the iteration,and the multi solution of the inversion is reduced.Through the calculation of the multi-layer theoretical model,the correctness and reliability of the constrained inversion algorithm are proved.It is used in the inversion calculation of the measured data of the transient electromagnetic method.The vertical distribution of the inversion resistivity is consistent with the data of the known stratum,and the abnormal area is verified by drilling,and the result is reliable.