Near Field Unit And Data Processing Design Of Metal Casing Detector

Metal casing is widely used in oil drilling operation. The metal casing corrosion and perforation phenomenon seems to be inevitable, because of the long-term impact of stratigraphic substance, high temperature, high pressure and so on. Therefore, an accurate asseseement of the situation of the corrosion casing has very important value and practical significance.‘Near field unit and data processing design of metal casing detector’ is a sub-project of national science and technology major project, whose purpose is to design a method of reflecting the attributes of metal casing, and to provide reliable basic data for detecting casing defects and calculating the thickness accurately. Based on the theory of near field eddy current and the requirements of well logging, this dissertation completed the hardware circuit and software design of near field unit, realized the algorithm which can invert the metal casing attribute.According to the near field eddy current theory of near field detector unit, the dissertation firstly designed the parameters of double coil used in the practical engineering; Secondly, the theory modle of coil transmission impedance was set up in the near field area of the metal pipe, from the coil impedance expression, we can get an expression about electromagnetic properties of the metal pipe. Then the environment was simulated with the finite element simulation software(ANSYS), which can establish the theoretical database of the trans-impedance of NFEC(Near-Field Eddy Current) area. In the meantime, the theoretical value of transmission impedance was calculated in the MATLAB. Nextly, in the engineering development, according to our practical demand, the signal processing included the conditioning of transmitting signal and receiving signal, and the main part was digital signal processing(DSP), analog signal processing was complementary such as amplification circuit and filter circuit. The phase between transmitting signal and receiving signal was measured accurately through the circuits. Finally, according to the relationship between the theoretical value and the testing phase, the dissertation expounded the LM+QN(Levenberg-Marquardt and Quasi-Newton) and LS-SVR(Least squares support vector regression) inversion algorithm, and analyzed the related physical properties such as inner diameter of the pipe and magnetic permeability from the actual logging data. At the last, the dissertation compared the reliability and superiority of these two algorithm.Through the instrument system debugging and analysis of test data processing, the experimental result verified the feasibility and detection precision of metal casing detector, and proved that the instrument reached the design requirements of measuring the damage.