Remote Field System And Data Processing Design For Multi-frequency Eddy Current Casing Damage Detector

Pipeline corrosion detection is a research hotspot in the field of oil well logging. However the current advanced technology is mastered by foreign logging service company. In order to break the technical monopoly, this dissertation develops a brand-new casing damage detector based on the theory of multi-frequency eddy current. RFEC technology is the core of the dissertation, which has advantages of high detection efficiency and high precision. By detecting the weak electromagnetic signal in remote field area, pipeline corrosion detection and inversion imaging of pipe wall thickness are realized.According to the remote field eddy current detection and weak signal detection theory, a complete casing damage detection model is established based on detailed analysis of measured signal. Combined with the theory of analog channel de-noising processing and digital phase sensitive detection algorithm, the remote-field signal detection circuit system and underlying software are designed and realized. The system consists of emission circuit and detection circuit. Low frequency emission circuit is designed in the dissertation based on SPWM principle. Detection circuit reduces hardware complexity through the channel multiplexed manner. The analog part adopts low-noise instrumentation amplifier with high precision, which can provide a high signal-to-noise ratio input for backward digital signal processing system. A FPGA+DSP type structure is used in the system, and the adopted digital signal processing algorithm has been demonstrated. Besides the function of internal hardware has been distributed rationally, which can achieve the high efficiency and low noise acquisition.Compared with the conventional remote field detection system, the dissertation has innovation points as follows. Adds rapid test mode, the instrument can be applied to more variety of scenarios; Reduces noise produced by emission circuit which are interfered with logging power system; Improves instrument testing process, such as the air and ground pipe scaling.Finally, the dissertation conducted a series of experiment and field logging. The debugging processes of remote field detection are divided into a circuit-level and system-level. The dissertation presents the results of a specific debug, which verifies the integrity functions of instrument. Through the analysis of field test results, the feasibility of casing damage detector and the ability to differentiate tiny defects are verified.