回线源三维地—井瞬变电磁法FDTD数值模拟

3Dimensions FDTD Numerical Simulation on the Down-hole TEM Field with a Loop Source

采用时域有限差分方法(FDTD),以回线源作为激发源。对均匀半空间和垂直断层面进行正演模拟。分析得出:在均匀半空间中,随观测时间延迟,感应电位先增大后减小,响应极大值向下移动;瞬变场在垂直断层面产生突变,在曲线上表现为峰值,低阻体产生响应直观明显,而高阻体响应无变化;对含有低阻体垂直断层面进行正演模拟,异常响应随断层面两侧异常体的电阻率比值增大而增强,识别能力强。研究结果为定性解释地—井瞬变电磁法异常和判断断层面提供参考依据。

The finite-difference time-domain （FDTD） is adopted in this paper and a large loop source is regarded as excitation source. The uniform half space and the vertical fault are forward simulated. This analysis shows the induced electric potential gradually becomes smaller after enlargement and the maximum value of response moves down with the obser- vation time delay in uniform half space. The transient electric field generated mutations and a peak appeared in the curve. The low conductive responds obviously and high conductive have no change. The vertical fault with the low conductive is also forward simulated. The abnormal response becomes intensified with the resistivity value of the two sides of abnor- mal bodies at the fault becomes larger, and the ability of identifying is stronger. Therefore, this paper provides the qualitative interpretation for the down--hole TEM anomaly and ref- erences for determining the vertical fault.