油井流动成像束状探测电磁场

为了克服油井流动成像电磁探测的"软场"效应,提高成像质量,本文从测量物理模型出发,采用在轴向上屏蔽和径向上聚焦的方法构建束状探测场,通过有限元仿真计算电势分布以及测量敏感场,发现轴向上屏蔽后的电势分布均匀平坦,从而探测电磁场可以简化为二维场;径向上聚焦后敏感区域主要集中在发射电极和接收电极之间的束状区域内,敏感场呈马鞍状,其中间敏感性明显加强.模拟流动实验测量结果表明,束状探测电磁场的测量信号较强,成像质量明显提高.

Fascicular electromagnetic field for electromagnetic tomography in multiphase flow well logging

In order to solve the "soft-field" effect of electromagnetic detection and improve imaging quality for electromagnetic tomography in multiphase flow well logging, analyzing the sensor physical model, the fascicular electromagnetic field is built by the methods of shielding in the axial direction and focusing in the radial direction.The electromagnetic field of a well is divided into two planes. In the axial direction, we add two same signals to the main measuring electromagnetic signal up and down, which can suppress vertical divergence of the main signal. Its shape looks like a pie. In the radial direction, we add two same signals to the main measuring electromagnetic signal on the left and right, which can suppress horizontal divergence of the main signal. The measured field is compressed in the middle field. Then the potential distribution and sensitivity field of the two planes are calculated by the finite element method (FEM). The data of detected signal are measured by flow experiments.From the FEM results analysis, by method of shielding, in the axial plane, the potential gradient changes little and the potential distribution is more homogeneous and flatter. The potential of the middle field is enhanced and the measured signal is raised to 30 mV. The potential does not change along axial direction. The 3-dimensional electromagnetic field can be simplified into a 2-dimensional field. By the method of focusing, in the radial plane, the potential distribution is more homogeneous and flatter. The measured signal is raised to 60 mV. The measured sensitive field is not only concentrated nearby the transmitting electrode and measuring electrode, but also has a saddle-shape within the fascicular region from transmitting electrode to measuring electrode, and becomes more sensitive in the inner region. The sensitive field is more homogeneous and suffers from smaller influence. From the flow experimental results, it could be concluded that the data of measured signal are largest and the response characteristics of signal curves are more in agreement with the laws by the fascicular electromagnetic field. It could be more exact to identify the flow pattern. The velocity of image reconstruction is faster and the images are clearer.Using the methods of shielding and focusing, the fascicular electromagnetic field can be built in the electromagnetic flow imaging logging. It increases the sensitivity of the middle position on the flow section and effectively restrains the "soft-field" effect in electromagnetic detection, and the imaging quality is better.