基于轴向线圈半圆周测量的随钻方位电磁波界面远探测方法研究

Although the azimuthal electromagnetic propagation resistivity tool employing titled-coil or cross-coil antennas to detect the location and azimuth of interface, it is difficult to increase depth of investigation (DOI) due to the weak signal. However, if we change the way of measurement, e.g. employing a modified axial-coil antenna with half electromagnetic shield to measure the electromagnetic (EM) field, it will achieve deep DOI. In this reach project, we plan to simulate the tool response with half-measuring axial-coil and study the application of this new measurement on detecting the interface. Firstly, we solve the EM field efficiently in both horizontally and cylindrically multilayered formation using the pseudoanalytic method in which we introducing the coefficients consisted of the location of interface and/or the ratio of cylindrical functions to obviate the overflow problem. Meanwhile, the finite element method is also used to analyze the EM field reflected by the interface and help to design new measuring way. Secondly, we simulate the tool response to interface in highly and horizontal wells, and analyze the effects of the drilling collar, borehole, and eccentricity. Finally, we reduce or eliminate the anisotropic effect by symmetric receiver coil antennas, and set up the database and the correction rules for borehole and eccentricity, furthermore, we finish the 1D inverse algorithm for the location and azimuth of the interface. Our work will provide a novel idea and theoretical basis to a new azimuthal electromagnetic propagation resistivity tool.

尽管随钻方位电磁波仪器采用倾斜或正交线圈结构探测地层界面位置及方位，但因界面信号弱，在现有仪器长度下难以实现远探测。改变测量方式，将轴向缠绕线圈的半圆周电磁屏蔽，利用余下的半圆周测量电磁场，则有用信号增强，可实现界面位置及方位远探测。本项目拟从理论上模拟与研究这种新测量方式在界面远探测上的应用。首先采用伪解析算法实现电流环在各向异性水平层状及圆柱状多层偏心模型中电磁场快速计算，引入边界位置及特殊函数比值的广义反射\透射系数消除数值溢出问题增加计算稳定性；同时结合有限元算法分析界面反射电场分布特征，设计探测方位电场天线结构；然后模拟大斜度井及水平井中界面响应规律；考察钻铤、井眼、偏心等环境因素对半圆周测量的影响规律；最后优化对称双接收线圈参数减弱电导率各向异性影响，建立井眼、仪器偏心数据库及校正规则，实现层界面位置及方位一维快速反演。为方位电磁波远探测仪器研制提供理论依据，开阔研究思路。

开发电磁波远探测技术可弥补测井与地震资料探测范围的空白，对复杂油气储层的勘探开发及动态检测具有重要意义。当前仪器主要采用倾斜或正交线圈结构探测地层界面位置及方位，其缺点是源距过长、信号弱。本项目采用轴向发射-轴向接收的半圆周测量方式，以期实现短源距下的电磁信号远探测。主要研究内容包括：（1）以电场矢量特征为基础的半圆周测量电磁远探测的工作原理研究；（2）水平层状及圆柱状分层各向异性地层中电磁场解析算法研究；（3）半圆周测量天线的结构设计与优化。已取得的重要研究成果有：（1）通过理论分析及数值模拟阐释了以电场矢量特征为基础的半圆周测量电磁远探测的工作原理；（2）实现了半圆周电场测量天线的工程设计；（3）与中石油测井有限公司合作，实现了实验样机的研制与测试；（4）发表学术论文8篇，培养博士研究生1名。科学意义：（1）当前电磁波测井工作原理及仪器设计主要依据磁场矢量分布特征及其测量，本项目开展了以电场矢量分布特征分析及测量的电磁波测井工作原理研究，丰富了电测波测井理论。（2）开展了理论模拟与实验测试的对比研究，凝练了从基础理论到仪器工程设计过程中的核心问题，为进一步的理论工作明确了研究方向。