一种新型三分量共面线圈系结构研究

New coplanar coil system based on the tri-axial induction logging

针对现有三分量感应测井共面线圈系趋肤效应影响严重和负响应区域较大等问题,提出了一种新的2发射1接收共面子阵列结构,以解析法实现正演模拟,应用层边界的切向连续,引入Bessel函数求解磁赫兹矢势,得到磁场强度的水平分量。推导新共面线圈系视电导率的解析解,对比新共面线圈系与目前共面线圈系在均匀地层中的响应特性和Born几何因子响应特性。分析工作频率、副发射线圈位置和匝数以及比例系数α对新共面线圈系响应特性的影响。结果表明,仪器工作频率越高,比例系数α越大,趋肤效应越严重;副发射线圈匝数越多,接收信号越大。与目前共面线圈系相比,新共面线圈系增大接收信号;减小趋肤效应影响;负响应区域明显减少;井眼影响近似为线性影响。通过分析发射线圈在井眼周围的涡流分布特性,揭示了新共面线圈系减小趋肤效应影响和降低负响应的机理。研究成果对三分量阵列感应测井仪器设计和应用具有重要的理论和实际意义。

In view of the serious skin effect and relatively large negative response area in the coplanar coil system of existing triaxial array induction logging tools,a new coplanar subarray configuration is presented consisting of two transmitters and one receiver. Firstly,the forward modeling is accomplished by analytic method which introduces Bessel function to solve Hertz vector potential by tangent continuity of the layer boundary,and the horizontal component of the magnetic field intensity is obtained. And the analytical solution of the apparent conductivity is derived for the new coplanar coil system. Secondly,Born geometric factor response characteristics and response characteristics in homogeneous formation are contrasted for two coplanar coil systems. In further,this work analyzes the influences of operating frequency,position and turns of the secondary transmitter coil and coefficient α on the response characteristics of the new coplanar coil system. The results show that the higher operating frequency and the greater coefficient α causes the more serious the skin effect. The more turns of the secondary transmitter coil leads to the greater received signal. Compared with the current coplanar coil system,the new coplanar coil system increases the received signal and reduces the skin effect. In addition,the negative response area is significantly decreased and borehole effect is approximately linear. The new coplanar coil system mechanisms is revealed for reducing skin effect and negative response through analysis of the distribution characteristics of eddy current of the transmitter coil. In summary,this work can provide a theoretical and practical significance for designing and application of triaxial array induction logging tools.