调校环境金属体对阵列感应测井信号的影响分析

Influence of Surrounding Metal Body on Signals of Array Induction Logging Tool

阵列感应测井仪器在进行参数调校时周围环境金属体对其具有非常严重的影响。设计基于球形求解区域外围加映射无限元的计算模型,解决金属体电导率和空气电导率相差多个数量级难以准确计算以及网格数量多计算时间长等问题,提高了计算精度、迭代收敛性以及计算稳定性。计算小金属体和柱形金属体对仪器影响,小金属体对阵列感应测井仪器响应具有与几何因子相反的特性;柱形金属体对每个阵列的影响随距离增大呈现快速振荡衰减,3m以外的影响可以忽略。实际测试验证了同样的特性,但影响更严重。计算模拟金属刻度环和刻度电阻的影响,验证最佳刻度点选取的有效性。当刻度电阻大于4Ω,测量信号近似线性变化;小于4Ω时,测量信号非线性逐渐增大。这些结果对阵列感应测井仪器的调校和测试环境设计具有重要的实际意义。

The surrounding metal body has a very serious influence on the measurement of an array induction tool when we adjust the tool parameters.Based on the spherical solving region and the peripheral with mapping infinite element,a calculation model is designed,which solves many problems,such as the difficulty to accurately calculate responses at the multiple order magnitude between metal conductivity and air conductivity,and the long computing time for many grids,and also improves the computing precision,convergence of iterative and stability of the calculation.Influence of small metal body and large metal body on a tool is calculated.The analysis shows that the metal material effect on the array induction responses has an opposite characteristics with the geometric factor.Cylinder metal effect on each array is a rapid oscillation damping change with distance.When the distance between the metal and tool is greater than 3m,the influence can be ignored.The actual test verifies the same characteristic,but the effect is more serous.A numerical model is designed to model the effect of the metal ring and scale resistor on measurement.It verifies the validity of the best scale point selection.When the scale resistance is less than 4Ω,the measured signal presents gradually nonlinear change.When the scale resistance is greater than 4Ω,the measured signal approximately is linear,less than 4Ω,and becomes nonlinear.These results have an important practical significance in the test of the array induction and design of the tool adjusting environment.