A New LoggingWhileDrilling Method for Resistivity Measurement in OilBased Mud Resistivity logging is an important technique for identifying and estimating reservoirs. Oilbased mud (OBM) can improve drilling efficiency and decrease operation risks, and has been widely used in the well logging field. However, the nonconductive OBM makes the traditional loggingwhiledrilling (LWD) method with low frequency ineffective. In this work, a new oilbased LWD method is proposed by combining the capacitively coupled contactless conductivity detection (C4D) technique and the inductive coupling principle. The C4D technique is to overcome the electrical insulation problem of the OBM and construct an effective alternating current (AC) measurement path. Based on the inductive coupling principle, an induced voltage can be formed to be the indirect excitation voltage of the AC measurement path. Based on the proposed method, a corresponding logging instrument is developed. Numerical simulation was carried out and results show that the logging instrument has good measurement accuracy, deep detection depth and high vertical resolution. Practical experiments were also carried out, including the resistance box experiment and the well logging experiment. The results of the resistance box experiment show that the logging instrument has good resistance measurement accuracy. Lastly, the results of the well logging experiment indicate that the logging instrument can accurately reflect the positions of different patterns on the wellbore of the experimental well. Both numerical simulation and practical experiments verify the feasibility and effectiveness of the new method.

Research on Features of Pipeline Crack Signal Based on Weak Magnetic Method Quantitative online detection of microcracks in longdistance oil and gas pipelines is an international problem, and the effective detection method is still lacking. In this paper, a mathematical model of nonuniform distribution of crack magnetic charges is established based on the stress distribution laws of pipeline cracks under internal pressure. The weak magnetic signal characteristics of pipeline cracks with different sizes are analyzed. The internal pressure increasing factor of weak magnetic signals are extracted to analyze the corresponding relationship between crack size and weak magnetic signals. The experimental study of the X70 pipeline is carried out. The results show that the axial component of the weak magnetic signal at the crack has a maximum value near the tip, and a minimum value appears in the middle of the crack. The internal pressure increasing factor is introduced to quantify the weak magnetic signal, the crack is in a safe state (not expanding) when the internal pressure increasing factor is positive, the weak magnetic signal has a linear relationship with the crack size. However, the crack is in a dangerous state when the internal pressure increasing factor is negative, and the pipeline crack will expand as the internal pressure increases.