复杂形态回线源的地—井瞬变电磁多分量响应特征分析

doi:10.11720/wtyht.2025.2486

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Abstract

In actual exploration, the surface-to-borehole transient electromagnetic (TEM) method is prone to be affected by irregular transmitter loops and inclined boreholes, resulting in increased measurement errors of the three-component induced magnetic fields and decreased interpretation accuracy. By establishing surface-to-borehole TEM method-based three-component measurement models under the excitement of transmitter loops of various shapes, this study derived the calculation formulas for surface-to-borehole TEM responses under inclined boreholes through coordinate transformation. Then, it achieved one-dimensional forward modeling of the full-space TEM field using a numerical filtering algorithm. The calculation results of multiple typical models indicate that the three components of the transient magnetic fields were significantly influenced by the shapes of the transmitter loops, with the impacts on horizontal components x and y far more significant than those on vertical component z. The transmitter loops of regular polygons with even edges as the sources exhibited uniform and symmetric distribution of the TEM fields of the three components. Under the condition of the same perimeter, a greater number of edges of the transmitter loops associated with greater primary field energy excited by the loops. Therefore, rectangular transmitter loops as the sources prove the most cost-effective. The inclination and offset primarily affected the amplitude of the three-component responses. In contrast, the borehole azimuth mainly influenced the sign of the horizontal components, bearing rich information on location. Therefore, in the exploration using the surface-to-borehole TEM method, it is necessary to accurately determine source paths and the geometric morphologies of boreholes to make essential corrections, thus improving the accuracy and reliability of interpretations.

Key words： surface-to-borehole transient electromagnetic method three-component response response characteristic transmitting source

Received: 10 November 2023 Published: 22 April 2025

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	Articles by authors
	Zhi-Xin WANG
	Ju-Zhi DENG
	Hui CHEN
	Chang-Kai QIU
	Hui YU
	Min YIN
	Min FENG

Cite this article:

Zhi-Xin WANG,Ju-Zhi DENG,Hui CHEN, et al. Analysis of multi-component response characteristics of surface-to-borehole transient electromagnetic method with complex-shaped loop source[J]. Geophysical and Geochemical Exploration, 2025, 49(2): 360-369.

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https://www.wutanyuhuatan.com/EN/10.11720/wtyht.2025.2486 OR https://www.wutanyuhuatan.com/EN/Y2025/V49/I2/360

Borehole TEM system model with arbitrary loop sources

Numerical solution and Analytical solution comparison

Comparison of results for the irregular loop model example

Four loop source shapes

X-component response characteristic diagram of transient field of four loop sources

Z-component response characteristic diagram of transient field of four loop sources

Three-component response curves of different shape of sources
(dashed lines indicate negative symbols)

X and Z component response curves of different well offset distances (dashed lines indicate negative symbols)

U and A component response curves of different well inclinations
(dashed lines indicate negative symbols)

X and Y component response curves of different well orientations
(dashed lines indicate negative symbols)

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