The Resistivity Imaging LWD Method Suitable for Oil-Based Drilling Fluid

The goal of this study was to solve the problem of drilling fluids blocking circuits and losing signal during the logging process. Oil-based drilling fluids are prone to blocking the DC circuit and hence invalidating conventional resistivity when using the LWD method. In order to solve this problem, researchers proposed implementing the capacitive coupling-based non-contact conductance detection technology with a resistivity imaging LWD method suitable for oil-based drilling fluids. This paper summarized the main methods of resistivity measurement while drilling, and introduced the principle and characteristics of capacitive coupled non-contact conductance detection technology. The azimuth logging simulation model for oil-based drilling fluids was established by combining capacitive coupling principle and inductive coupling principle. Then, the logging simulation experiment under various working conditions was carried out with this model, and the relationships between the circumferential position and current amplitude, circumferential position of electrode and the current phase, as well as the imaging principle of button electrode were analyzed. The simulation results showed that the button electrode had azimuth detection capability, and the proposed logging method was feasible. A surface simulation logging system was designed to carry out the indoor test of azimuth logging. The test found that this logging system may to achieve formation imaging and measure the formation dip angle, and the relative error between the test result and the actual formation dip angle is only 4.7%. The study showed that the proposed resistivity imaging LWD method is able to perform lateral resistivity measurements while drilling in oil-based drilling fluids, and make the measured resistivity imaging to obtain the reliable logging results.