三分量阵列感应共面线圈系井眼影响研究

三分量阵列感应测井仪器是测量复杂地层信息的重要工具,消除共面线圈系的井眼影响是仪器设计与应用的关键。应用有限元软件,数值计算分析居中井眼中三分量阵列感应的共面线圈系与共轴线圈系的响应特性,对比共面线圈系实验室建模仿真与现场试验结果。结果表明:除最短子阵列,其余共面子阵列的井眼影响与共轴子阵列显著不同,井眼影响导致测井响应为负值;最长子阵列虽然井眼影响小,但趋肤效应影响严重,地层电导率测量范围比共轴线圈系小得多。通过计算分析共面线圈系在井眼周围不同泥浆和地层电导率时的涡流分布特性,揭示了共面线圈系与共轴线圈系差别较大的原因。提出新的2发1收线圈系结构,从几何因子角度分析了它在减小井眼影响、降低测井负响应等方面的优势。研究成果为三分量阵列感应测井仪器的研制和应用奠定了理论基础。

Study of borehole effect of tri axial array induction on coplanar coil system

The tri-axial array induction logging tool is an important tool for measuring complex formation information,but the key of design and application is to eliminate borehole effects of coplanar coil systems.The response characteristics of coplanar coil systems and coaxial coil systems of the tri-axial array induction are analyzed numerically in the center hole by the FEM,and field experiment results are compared with modeling simulation on the coplanar coil systems.The results show that the borehole effects of coplanar coil systems are significantly different from that of coaxial coil systems besides the shortest sub-array.The borehole effect causes the negative logging response.For the longest sub-array,although the borehole effect is week,its skin effect is serious and the measurement range of formation conductivity is smaller than that of the coaxial coil systems.It reveals the reason that the greater difference is occurred between the coplanar coil systems and the coaxial coil systems through the eddy current distribution of coplanar coil systems around the borehole at different mud and formation conductivity.A new coil system which has two transmitters and one receiver is raised and its advantages are analyzed on the decreasing borehole effect and reducing negative response from the geometrical factor.The research lays a theoretical basis for the development and application of the tri-axial induction logging tool.