套管空间磁场分布特征实验研究

Experimental study on spatial magnetic field distribution characteristics around casing strings

摘要:

针对被动磁测距（PMR）技术中对套管磁场分布特征认识不足的问题，开展了套管空间磁场分布规律研究。搭建了由FVM-400型三轴磁通门磁力仪及无磁支架组成的测试系统，基于磁化理论分析，采用控制变量法对133/8、95/8 in典型规格套管进行单根及组合工况下的轴向与径向磁场测试。结果表明：套管轴向磁场呈现类正弦波动特征，磁场梯度峰、谷值集中于接箍及端部区域；套管径向磁场强度随距离呈指数衰减；本实验条件下，套管轴向距端面2 m、径向距轴线8 m以外的磁场趋近于地磁场基准值；组合套管磁场形态受接箍磁极组合方式影响显著，同向组合在接箍处形成单一强峰，反向组合则呈“双峰双谷”特征，且同向组合的磁场强度与影响范围更大；相同规格套管存在剩磁个体差异。研究揭示了套管尺寸、剩磁及磁极组合对磁场空间分布的影响机制，为完善PMR技术理论模型、提升强干扰背景下磁场信号解析能力提供了实验依据与基础数据支撑。

Abstract:

To address the insufficient understanding of casing magnetic field distribution characteristics in passive magnetic ranging （PMR） technology， this study investigates the spatial magnetic field distribution laws around casings. A testing system consisting of an FVM-400 three-axis fluxgate magnetometer and non-magnetic supports was established. Based on magnetization theory analysis， axial and radial magnetic field tests were conducted on typical 133/8 and 95/8 inches casings under single and combined conditions using the control variable method. The results indicate that the axial magnetic field of the casing exhibits sinusoidal-like fluctuation characteristics， with the peak and valley values of the magnetic field gradient concentrated in the collar and end regions. The radial magnetic field intensity decays exponentially with distance. Under the experimental conditions， the magnetic field approaches the geomagnetic field reference value at distances greater than 2 m axially from the end face and 8 m radially from the axis. The magnetic field morphology of combined casings is significantly influenced by the magnetic pole combination at the collar： same-direction combinations form a single strong peak at the collar， while reverse combinations exhibit "double-peak and double-valley" characteristics， with the former showing greater magnetic field intensity and influence range. Additionally， casings of the same specification exhibit individual differences in remanent magnetism. This study reveals the influence mechanisms of casing size， remanent magnetism， and magnetic pole combination on the spatial distribution of the magnetic field， providing an experimental basis and fundamental data support for refining PMR theoretical models and enhancing magnetic field signal analysis capabilities under strong interference backgrounds.