近钻头电阻率测量理论及响应模拟

Theory and Response Simulation of NearBit Resistivity Measurement

利用有限元素法仿真软件,对采用螺线环型天线的近钻头电阻率测量工具进行建模仿真.对发射源进行等效变换,建立轴对称二维和三维磁流源等效模型.利用这2种模型,分析工作频率、地层电阻率、钻铤与天线尺寸等参数对信号衰减的影响规律,并对该仪器的前向和径向探测深度以及纵向分辨率指标进行分析和评估.结果表明,螺线环型天线能有效测量钻头周边电阻率信息,2种等效模型能有效分析信号的衰减规律和仪器的探测特性.研究给出的建模方法和得到的结论对研制该类仪器和分析仪器的响应规律具有重要的指导意义.

The near-bit resistivity tool with a toroid antenna is simulated using finite element simulation software.Then equivalent axisymmetric 2D and 3D magnetic flux source models are built after equivalent transformation of the toroid transmitter.And finally,using the two models,the influences of working frequency,formation resistivity and the sizes of drill collar and antenna are analyzed on signal attenuation,and the front and radial detection depth and the vertical resolution are analyzed and evaluated.The results show that the toroid antenna can effectively measure the resistivity around bit,and the two equivalent models can analyze signal attenuation and detecting characteristics.The modeling methods and the conclusion play an important role for developing this type of logging tools and analyze the response law of the tools.