| 摘要: |
| 针对井中瞬变电磁全区视电阻率定义求解和解释方法开展研究。依据均质全空间瞬变电磁场解析式计算不同采样时间或装置条件下感应电压响应,认识到响应值在电阻率取值范围的全区间或部分区间内保持单调性。根据“牛顿-下降”最优化原理,给出一种井中瞬变电磁全区视电阻率求解方法,通过均质全空间瞬变电磁场响应试算结果与介质真电阻率对比验证该方法的精度和适用性。建立典型径向及垂向分层地电介质模型,通过时域有限差分法模拟计算瞬态场感应电压响应,并进行全区视电阻率换算分析。结果表明:视电阻率是不同时刻电磁场作用范围内所有电性体的综合反映,由全时段视电阻率结果识别全空间介质的径向及垂向电性情况具有一定可行性,各时道的视电阻率值可作为推断地电结构等信息的依据。 |
| 关键词: 全区视电阻率 井中瞬变电磁法 磁源 牛顿-下降法 径向分层模型 |
| DOI：10.3969/j.issn.1673-5005.2015.06.009 |
| 分类号::P 631.8 |
| 基金项目:国家自然科学基金项目(41304082);河北省自然科学基金项目(D2014403011);中国石化科技攻关项目(P13111) |
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| Study on interpretation method of all-time apparent resistivity for transient electromagnetic method in borehole |
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MENG Qingxin1, PAN Heping2, MA Huolin2
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(1.Shijiazhuang University of Economics, Shijiazhuang 050031, China;2.Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, China)
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| Abstract: |
| The all-time apparent resistivity calculation and interpretation method for magnetic source TEM (transient electromagnetic method) in borehole was investigated. The induced electric voltage responses were calculated for different sampling time or different device conditions by using the homogeneous whole space transient electromagnetic field formula, and the computations showed that the TEM response remained monotonicity in resistivity value range or part of the range. According to the "Newton-Downhill" principle of optimization, a borehole TEM all-time apparent resistivity calculation method is presented. Compared with the all-time apparent resistivity results of uniform whole space transient electromagnetic response from real resistivity of the medium, the method is proved to be accurate and applicable. Radial-layered and vertical-layered geoelectric models are built, on which the transient electromagnetic field responses are calculated using finite difference time domain method and are then converted to apparent resistivity. The results show that:the apparent resistivity is an integral of all electrical target characteristics of electromagnetic field at different times; the radial and vertical electrical characteristics of the whole space medium are recognized by apparent resistivity results of full time channels; and the all-time apparent resistivity results of different periods can be used as a basis for inferring geoelectric structure information. |
| Key words: all-time apparent resistivity borehole transient electromagnetic method magnetic source Newton-Downhill algorithm radial-layered medium |
