Numerical Simulation of Pig Motion in Two-Phase Flow Pipelines in the Presence of a Leak

Abstract

In the oil and gas industries, it is important to keep pipelines operating at the highest level-of efficiency. This means that a pipeline should not undergo events that may reduce the amount of pumped product at the end of the line. Examples of these events are the existence of debris moving along with the flow, or wax deposited on the pipe wall or the development of a crack or hole on the wall that may lead to the occurrence of a leak. The use of pigs (Pipeline Inspection Gauge) is one of the most common tools for inspection and cleaning of the pipe to restore the optimum pipe operation, despite the uncertainties and risks associated with its passage inside a long duct. For this reason, it is important to follow the pig motion inside the pipeline using numerical simulations. The velocity of the pig depends on the flow dynamics and the pig’s flowing characteristics. This paper presents a mechanical model for the pig motion, along with a numerical scheme, to obtain approximate solutions for the resulting initial-boundary-value problem that describes the pig motion in a transient gas/liquid-flow inside the pipeline in the presence of a leak. The model is formulated as an initial-boundary-value problem of hyperbolic nature. The system of non-linear partial differential equations is discretized within the finite-volume framework and solved using the flux corrected-transport (FCT) method, which is second-order in space. A situation involving a leakage of 10% of total inlet mass flow was simulated and the results are presented for the pig velocity history and for the distribution of flow pressure, velocity and liquid volume fraction along the pipe. In order to validate our results, the commercial software OLGA®, well known in the oil and gas industry, is used for comparison.