A TRANSMISSION-LINE MODEL FOR ELECTRICAL LOGGING THROUGH CASING
A TRANSMISSION-LINE MODEL FOR ELECTRICAL LOGGING THROUGH CASING
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DOI：
10.1190/1.1443388
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发表时间：
1993-12
期刊：
影响因子：
3.3
通讯作者：
A. Kaufman;W. E. Wightman
中科院分区：
文献类型：
--
作者：
A. Kaufman;W. E. Wightman
套管井中的电测井是一个热门课题。本文发展了地层电阻率垂直变化和套管电导变化的常规套管电测井物理响应理论。该理论是为一个四电极探头与一个电流电极，和三个接收器电极，测量电流泄漏到地层。本文中的所有理论发展都是使用近似传输线理论导出的。首先导出阵列系数的表达式，然后用于获得地层视电导率的表达式。然后建立了阵列系数、几何因子与套管电导之间的关系。这一步骤导致了测量套管电导的方法。已知套管电导，阵列对地层电导率的垂直变化的响应是可测量的。已确定，当阵列长度小于地层厚度时，测量的视电导率等于地层的真实电导率，这与正常和感应测井的情况不同。还确定了当套管基本上超过电极阵列的长度时，可以在有限长度的套管内精确地进行表观电导率的测量。本文的结果表明，在常规套管柱下穿层状沉积地层的威尔斯井中，套管电测井是可能的。
Electrical logging in cased holes is a subject of strong current interest. In this paper we develop the conventional theory of physical responses of electrical logging through casing where the formation resistivity changes vertically and where the conductance of the casing varies. The theory is developed for a four-electrode sonde with one current electrode, and three receiver electrodes that measure current leakage into the formation. All the theoretical developments in the paper are derived using approximate transmission-line theory. An expression for the array coefficient is first derived and then used to obtain an expression for the apparent conductivity of the formation. Then a relation is established between the array coefficient, geometrical factor and conductance of the casing. This step led to a method of measuring casing conductance. Knowing casing conductance, the response of the array to vertical changes in formation conductivity is measurable. It was established, that when the array length is less than the thickness of the formation layer, the measured apparent conductivity is equivalent to the true conductivity of the formation, unlike the case of normal and induction logs. It was also established that measurement of apparent conductivity can be made accurately inside a casing of finite length when it essentially exceeds the length of the electrode array. The results contained in this paper show that electrical logging through casing is possible in wells with conventional casing strings that penetrate layered sedimentary formations.