This paper presents a method for the detection of multi-layer petroleum pipelines using electromagnetic induction. At the same time, the PIC32 chip is used as the main control chip to control the IGBT full-bridge circuit excitation coil, and the logging hardware system is designed and fabricated by amplifying and sampling signals. This paper also designed a comprehensive software that can cooperate with this system to accept CAN bus signals and analyze and plot data. The proposed solution provides a complete solution for electromagnetic flaw detection of multilayer petroleum pipelines.
Design background and meaningOil and gas field casing damage (hereinafter referred to as casing damage) is a common technical problem encountered in oil development to a certain period of time. Oilfields at home and abroad are bothered by this problem. With the application of various stimulation measures such as high-pressure injection, ultra-high pressure fracturing and the development of oilfield development time, mudstone water absorption creep, rock layer sliding, oil layer sand production, oil field development process, resurrection layer, perforation, natural earthquake, oil layer For reasons such as compaction, the problem of casing damage in oil and water wells in various oilfields will become more and more serious.
The oil well damage in China's major oilfields is very serious. In 1997, Daqing Oilfield damaged 576 wells in casing. In 2001, there were more than 700 casing damage wells. The entire oilfield has damaged more than 8,000 wells. As of April 2003, there were total casing damage in Shengli Oilfield. More than 5,400 wells.
The existence of a large number of damaged wells is not only the idle waste of fixed assets, but also leads to the gradual increase of the land grading and the deterioration of the reserve control, which in turn results in different losses of oilfield water flooding reserves and recoverable reserves. Therefore, casing damage Well is the bottleneck problem that restricts the stable production of oilfields. It develops the research and application of casing damage prevention and treatment technology, clarifies the mechanism of complex casing damage, seeks corresponding preventive measures, and prolongs the service life of casings. One of the topics is of great significance to improving the overall development efficiency of the old oilfield. In such an environment, logging shows an important role and is listed as one of the ten university departments of the petroleum industry.
At present, there are many methods for engineering logging tools for casing inspection, including caliper, ultrasonic imager and electromagnetic detector. Among them, the caliper has high requirements on the center of the instrument, and the eccentricity will cause measurement error, and the instrument is not suitable for wells with severely broken casing; the ultrasonic method is greatly affected by the drilling fluid, and if the density of the drilling fluid is large, the acoustic attenuation Severe, affecting the accuracy of detection, must wash wells and replace drilling fluid before testing, increasing labor intensity. The electromagnetic detector is based on the electromagnetic principle to give the evaluation of the integrity of the casing. It is not affected by the liquid in the well, the casing fouling, the wax formation and the attachment of the well wall, and the measurement accuracy is relatively high.
Russia's multi-layer column electromagnetic flaw detection imaging tool MID-K is the use of electromagnetic theory for flaw detection. In China, the research on electromagnetic flaw detection is also a hot spot, but most of them are concentrated on theoretical research. The performance and detection accuracy of the designed electromagnetic flaw detection logging system are not very good, so we want to design a chip based on PIC32 32-bit microcontroller. Electromagnetic flaw detection logging system with high performance and detection accuracy.
Basic principle of transient electromagnetic casing inspectionTransient electromagnetic method, also known as time domain electromagnetic method, is based on the theory of electromagnetic induction to pass a bipolar DC pulse to the transmitting coil. When the current in the transmitting coil changes, a magnetic field will be generated around it. For a magnetic field.
According to the theory of electromagnetic penetration in conductors, the magnetic lines of force pass through the tubing into the casing, generating induced currents in the tubing and casing, respectively. 
(As shown in Figure 1). After the end of the DC pulse, the secondary magnetic field generates an induced electromotive force in the receiving coil 
. If there is a crack in the casing or the oil pipe, especially the longitudinal crack, the induction current will be partially or completely cut off. Pathway, which will reduce the induced electromotive force Decay time.
Figure 1 Schematic diagram of probe detection
mathematical modelUsing the single-turn loop including the equivalent inductance Lc and the equivalent resistance Rc shown in Figure 2 to equivalent the induced current loop, the two have similar laws.
Figure 2 Schematic diagram of the equivalent circuit of a finite conductor
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