基于C^4D技术的油基钻井液随钻侧向电阻率测井信号检测

Signal detection of lateral resistivity LWD based on C^4D technique with oil-based drilling fluid

为了解决传统随钻侧向电阻率测井在油基钻井液下测量受限的问题,提出基于电容耦合非接触电导测量(C^4D)技术的信号检测方法与装置。首先构建基于C^4D技术的测井等效电路模型,然后采用数字相敏解调技术实现测井微弱信号幅值和相位的检测,依据所建模型可求得地层电阻率;同时,采用有限元仿真方法对模型的有效性以及所设计的测井响应特性进行研究;最后,设计1套模拟测井实验装置,并在多个激励频率下进行实验。研究结果表明:在20 k Hz工况下实验装置的测量性能较好;当等效地层电阻率为0.135~8.368 kΩ·m时,测量相对误差小于5%。

In order to solve the problem of measurement limits of traditional lateral resistivity logging while drilling（LWD） with oil-based drilling fluid, a method based on the capacitively coupled contactless conductivity detection（C-4D） technique was proposed for signal detection and the corresponding device was developed. First, an equivalent logging circuit model based on C-4D was established. Then, digital phase sensitive demodulation（DPSD） technique was introduced to detect amplitude and phase of weak logging signal, and formation resistivity was obtained by the established model. Meanwhile, finite element simulation was conducted to study validity of the model as well as response characteristics of the designed logging sensor. Finally, a simulated logging experimental device was designed, and the experiment was carried out at multiple excitation frequency. The results show that the designed device has good performance when excitation frequency is 20 k Hz, and corresponding relative measurement errors are less than 5% within equivalent formation resistivity range of 0.135-8.368 kΩ·m.