Multi-layer petroleum pipeline flaw detection system using electromagnetic induction
This paper introduces a novel method for detecting multi-layer petroleum pipelines using electromagnetic induction. The system employs the PIC32 microcontroller as the main control unit to manage the IGBT full-bridge circuit that drives the excitation coil. A logging hardware system was developed and fabricated, incorporating signal amplification and sampling techniques to enhance detection accuracy. In addition, a comprehensive software application was designed to work in conjunction with the hardware, capable of receiving CAN bus signals, analyzing data, and generating visual plots. This integrated solution offers an effective and reliable approach for electromagnetic flaw detection in multi-layer petroleum pipelines.
The design background stems from the widespread issue of casing damage in oil and gas fields. Casing damage is a common challenge faced by oilfields globally, often resulting from various factors such as high-pressure injection, fracturing, mudstone water absorption, rock layer sliding, sand production, natural earthquakes, and compaction. Over time, these issues lead to more severe casing damage, which significantly impacts well performance and operational efficiency.
In China, the problem of casing damage is particularly severe. For example, in 1997, Daqing Oilfield reported 576 damaged wells, and by 2001, this number exceeded 700. By 2003, Shengli Oilfield had over 5,400 casing-damaged wells. Such extensive damage not only represents a waste of fixed assets but also leads to increased land grading, reduced reserve control, and loss of recoverable reserves. As a result, casing damage has become a major bottleneck in maintaining stable oilfield production. Addressing this issue through improved prevention and treatment technologies is crucial for enhancing the overall development efficiency of aging oilfields.
Currently, several methods are used for casing inspection, including calipers, ultrasonic imagers, and electromagnetic detectors. However, each has its limitations. Calipers require precise centering, and eccentricity can cause measurement errors. Ultrasonic methods are affected by drilling fluid density, which can reduce detection accuracy. Electromagnetic detectors, on the other hand, are less influenced by well fluids, fouling, or wax buildup, making them more reliable and accurate for casing integrity evaluation.
Russia has developed the MID-K tool, which uses electromagnetic theory for multi-layer casing inspection. In China, research on electromagnetic flaw detection is ongoing, though most efforts remain theoretical. Existing systems often lack sufficient performance and detection accuracy. To address this, this study focuses on designing a high-performance electromagnetic flaw detection logging system based on the PIC32 32-bit microcontroller.
The transient electromagnetic method, also known as the time-domain electromagnetic method, involves sending a bipolar DC pulse through a transmitting coil. As the current changes, a magnetic field is generated around the coil. According to electromagnetic penetration theory, magnetic field lines pass through the tubing into the casing, inducing currents in both the tubing and the casing. After the pulse ends, the secondary magnetic field induces an electromotive force (EMF) in the receiving coil. If there is a crack in the casing, especially a longitudinal one, the induced current path is disrupted, leading to a reduction in EMF and a shorter decay time.
A schematic diagram illustrating the probe detection process is shown in Figure 1. Additionally, a mathematical model representing the equivalent circuit of a finite conductor is presented in Figure 2, where a single-turn loop with equivalent inductance Lc and resistance Rc is used to simulate the induced current loop. This model provides a foundation for understanding the behavior of electromagnetic signals during the inspection process.
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