井中激电三维反演存在多解性且计算时间长,制约了其由理论走向实际应用。针对这一问题,采用非线性共轭梯度(NLCG)反演方法,在反演目标函数中直接施加约束条件压制其解的非唯一性,也就是将介质电阻率取值范围作为先验信息和约束条件以惩罚函数法的方式引入到反演目标函数中。与常规三维电阻率反演目标函数相比,增加了不等式约束项的目标函数理论上可以压制反演的多解性。理论模型的反演结果表明,基于不等式约束的井中激电三维反演方法有效地改善了反演结果的精度,以惩罚函数法施加不等式约束条件的方式现实可行。
The 3D borehole induced polarization(IP)inversion is characterized by multiple solutions and long computation time,which restricts the 3D inversion of the borehole IP method to be put theory into practice.To solve this problem,in this paper we use the nonlinear conjugate gradient inversion method(NLCG)and constraints are directly imposed in inversion objective function to neutralize the non-uniqueness.By the way of penalty function method,the range of medium resistivity regarded as priori information and constraint conditions is introduced into inversion objective function.Compared with the conventional 3D resistivity inversion objective function,new objective function with an inequality constraint can suppress multiple solutions in theory.Inversion results of theoretical model show that the method effectively improves the inversion accuracy.It is also proved that inequality constraint condition is imposed by penalty function method is feasible.