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本文对地-井瞬变电磁法多分量响应进行计算分析。规则局部体瞬变场响应的计算方法与解释模型对于实际导电围岩模型的适用性较差,针对该问题,本文提出了一种基于地下瞬态电磁场数值模拟的计算分析方法。瞬变电磁场模拟方面,本文以时域有限差分法实现正演模拟,引入采用Gaver-Stehfest逆拉氏变换与Prony法的离散镜像法求解初始电磁场,应用透射边界条件保证迭代计算精度。通过均质半空间模型算例,证明该套方法可行。响应分析方面,设定含井旁目标体和导电围岩的地电模型,以上述方法对地下瞬态电场进行正演,以多分量观测装置为例换算感应电动势。通过对比各条件下瞬态电场与多分量响应,得出结论:地-井瞬变电磁多分量感应电动势响应反映了地下瞬态电场沿水平、垂直方向的梯度变化;响应特征取决于地层中瞬变场在不同条件下的“扩散、衰减、畸变”过程和观测位置的电磁场状态。本文的计算分析方法兼顾围岩背景场与局部体异常场,较之传统局部体瞬变场原理能够更全面的反映地质信息。
In this paper, the multi-component response of ground-well transient electromagnetic method is calculated and analyzed. In order to solve this problem, this paper presents a calculation and analysis method based on numerical simulation of transient transient electromagnetic field. In the field of transient electromagnetic field simulation, the finite difference method in the time domain is used to realize the forward modeling. The discrete image method using Gaver-Stehfest inverse Laplace transform and Prony method is introduced to solve the initial electromagnetic field. The transmisson boundary conditions are used to ensure the iterative calculation accuracy. Through a homogeneous half-space model example, this method is proved to be feasible. In the aspect of response analysis, the geoelectric model with target body and conductive rock surrounding the well is set up, and the transient transient electric field is staged by the above method. The multi-component observation device is taken as an example to convert the induced electromotive force. By comparing the transient electric field and multi-component response under each condition, it is concluded that the multi-component induced electromotive force response of ground-well transient electromagnetic field reflects the gradient along the horizontal and vertical direction of transient transient electric field. The response characteristics depend on the instantaneous Field under different conditions “diffusion, attenuation, distortion ” process and the electromagnetic field state at the observed position. The method of calculation and analysis in this paper takes into account the background field of surrounding rock and the local anomalous field, which can reflect the geological information more completely than the traditional local body transient field principle.