The effect of parallel pipeline parameters on the characteristics of gravity and magnetic surveys

Abstract

Parallel pipeline detection is a difficult problem in underground pipeline detection. Gravity and magnetic surveys have the advantages of convenient monitoring, high sensitivity, and high accuracy. Therefore, we used gravity and magnetic surveys to detect parallel pipelines. In this paper, the effect of parallel pipeline parameters on the characteristics of gravity and magnetic surveys is studied in order to find out the quantitative relationships between them and to provide the theoretical basis for inversion interpretation. When calculating the magnetic anomaly of a pipeline, we considered the demagnetization effect of the pipeline and determined its demagnetization coefficient to be 0.12 by numerical calculation. Parallel pipeline parameters include geometric parameters (such as outer diameter ratio, pipe axis spacing, buried depth, and azimuth, etc.) and physical parameters (density and magnetic susceptibility). The characteristics of gravity and magnetic surveys include not only the amplitude of abnormal peaks, the number of abnormal peaks, and abnormal peak spacing of gravity and magnetic anomaly curves, but also the detection error of gravity and magnetic surveys in parallel pipelines. We defined the relative error of the pipe axis spacing of parallel pipelines as the detection error. We established a forward model for parallel pipeline detection and analyzed the effect of model parameters on the characteristics of gravity and magnetic surveys. Results show that gravity and magnetic surveys cannot detect pipelines parallel to the measurement line and the magnetic survey can only detect pipelines with ferromagnetism. The amplitude of abnormal peaks is affected by all parallel pipeline parameters, while the number of abnormal peaks, abnormal peak spacing, and detection error are only affected by the outer diameter ratio, pipe axis spacing and buried depth. If the upper limit of the detection error is determined to be 10%, gravity and magnetic surveys of parallel pipelines have minimum discernible pipe axis spacing. Through further research, it is found that when the outer diameter ratio is 1, the minimum discernible pipe axis spacing is minimal. The minimum discernible pipe axis spacing increases linearly with the increase of buried depth. When all parallel pipeline parameters are identical, the minimum discernible pipe axis spacing of the gravity survey is greater than that of the magnetic survey. The research results show that the magnetic survey is more suitable for detecting parallel underground pipelines than the gravity survey, and the experiment of magnetic anomaly measurement of parallel pipelines also shows that it is feasible to detect parallel underground pipelines by the magnetic survey.