Magnetic Anomalies of Submarine Pipeline Based on Theoretical Calculation and Actual Measurement

Marine magnetic method is widely used for detecting and locating the submarine pipeline. In this paper, the theoretical calculation model of total-field magnetic anomalies (TMAs) of submarine pipeline was derived based on Poisson's equation. Taking a submarine gas pipeline for example, the TMA theoretical calculation and the verification sea test were carried out. Based on the calculation, the influences that the geomagnetic parameters, pipeline parameters, and measuring plane height had on the TMA characteristics of pipeline were analyzed. The TMA shape changed slightly with geomagnetic declination D and was significantly influenced by the azimuth θ of the pipeline. The corresponded location of the pipeline on the TMA profile varied with D seemed to be symmetrical with D = 0° as the center, but within 1.0 m, and changed greatly with θ with an offset distance of upping to 4.4 m. The TMA amplitude was linearly positively correlated with geomagnetic intensity T₀, quadratic difference of outer and inner diameters of pipeline d₁²-d₂², and susceptibility κ, respectively, and was inversely proportional to the square of measuring plane height R, and changed greatly with D, I, and θ but without obvious correlation. The TMA width changed greatly with I and θ, respectively, but without obvious correlation, and was approximately positively correlated with R. On the TMA profile that was perpendicular to the pipeline, there would be an obvious “pulse” anomaly on the smooth profile, and the location of pipeline corresponded a specific point near the TMA maximum point depending on D and θ, so that the accurate location of the pipeline needed to be corrected according to these two parameters, not just the TMA maximum point.