瞬变电磁法低阻薄层反演

Transient electromagnetic inversion for thin layer with low resistivity

瞬变电磁反演方法对瞬变电磁数据解释有极其重要的作用。在实际工程中,由于地下低阻薄层响应较弱,现有的反演方法很难将其分辨出来。文中基于正则化反演理论,提出了一种新的模型约束加权方法,对地层的光滑度施加了周期性大幅变化的权值,通过两次迭代可自适应的反演出低阻薄层区。小权值使模型对电性参数的大尺度变化有较高的敏感性,便于筛选出异常薄层;同时,与小权值交错分布的大权值能尽量保证反演曲线的连续性,降低反演的多解性。通过仿真验证,该方法对低阻薄层区的分辨能力比传统算法更高,对较厚区域低阻区的分辨能力与传统方法类似。该方法迭代稳定,不依赖地层先验信息,具有很高的工程实践性。

Inversion is an important tool for transient electromagnetic data interpretation. This paper proposes a novel weighing scheme with periodic vibration for roughness restriction based on the regularized optimization theory. The small weights make the models sensitive to reflecting parameters＇ great changes and thus it is easy to show the thin layer with low resistivity. The large weights distributed near small weights can make sure the continuity of the inversion results,which reduces the variety of the solution. Synthetic models show that this method has higher resolution for low resistivity thin layer than traditional ones and keeps the same resolution with traditional ones when inverting low resistivity large areas. In addition,this method converges stably and does not rely on a prior information about the ground structure,thus making sure its application in practice.