Leak detection in subsea pipeline: A mechanistic modeling approach with fixed pressure boundaries

This study shows how a subsea pipeline leak can be modeled in a mechanistic way. Special attention is paid to the implication of fixed-pressure boundary conditions at both upstream and downstream locations, which is relevant to the way the majority of field operations are actually performed. The use of fixed-pressure boundary conditions leaves the change in inlet total flow rate (Δq_tin) and the change in outlet total flow rate (Δq _tout) as two possible leak-detection indicators that can be monitored on a realtime basis. The two-phase flow of gas and oil mixtures in subsea pipelines is analyzed by using Beggs and Brill's correlations. The effect of different parameters on the mechanistic leak-detection modeling is also investigated, accounting for gas compressibility, backpressure of the system, pressure drop across the system, and gas/oil fraction at the leak. Also presented in this study is a new method to predict the change in inlet or outlet total flow rates (Δq_tin or Δq_tout) in a form of contours with dimensionless leak opening size (d_leak/D) and dimensionless leak position (x_leak/L) in x and y axes. This new style of reporting leak-detection indicators is believed to provide a convenient means to improve data interpretation in actual field practice and laboratory tests.