Slug flow induced oscillations on subsea petroleum pipelines

A slug flow load model is proposed to simulate the oscillations induced by the internal flow on pipelines conveying liquid and gas mixtures. The internal flow loads imposed on the pipelines are deduced and implemented in a 3D simulator of pipelines structural dynamics. These internal flow forces, due to gravity and to the curvature of the pipeline, are expressed in vector form providing generality to the formulation, which, combined with the 3D simulator, allows the analysis of a large variety of geometries. A computer code is implemented with the proposed model and tested against cases for which theoretical results can be calculated, displaying good agreement. Further, the model is used to simulate various slug flow conditions in deep water petroleum production risers - steel catenary riser and lazy wave configurations, demonstrating that these pipelines may present oscillations solely due to the internal flow, even when no other external excitations are present. This study also presents the effect of the slug frequency on the amplitude of oscillations of these risers, indicating that large oscillations are indeed possible. The flow load model accepts any valid combinations of gas flow rates and liquid flow rates; thus the pipeline designer may sweep a wide range of production conditions, detecting those that might pose the pipeline in danger, due to alternate stresses inducing fatigue. In general, the modeling algorithms developed in the present work may be inserted in any other pipeline simulator.