Severe slugging in deepwater risers: A coupled numerical technique for design optimisation

Abstract

This paper presents an improvised coupling technique for stress impact and dynamic response studies of a deepwater flowline-riser pipe system exposed to cyclic loadings resulting from severe slug flow. It involved partial coupling of transient multiphase flow simulator OLGA and structural finite element code ABAQUS. In this analysis, a parametric study was carried out where mass flow rates of 9.8 kg/s, 13 kg/s, and 16 kg/s were sampled in order to reflect the corresponding marginal flow rates of 6000 (950.4 m3/day); 8000 (1267.2 m3/day); and 10000 (1584 m3/day) barrels of oil per day (bbl/day) for a typically aged offshore oilfield presumed to be piped with a 10 inch (0.254 m) diameter subsea production pipe system. Numerical results obtained, have shown that the 6000 bbl/day flow rate imposed predominant stress at the riser base by producing maximum stress values of 64 MPa, 63 MPa, and 68 MPa in the axial, transversal and lateral global directions of the flowline-riser cross-section, respectively. This observation has further validated the severity of severe slug flow to low flow rate of reservoir fluids. With this and other data provided in this paper will enhance the fatigue design optimisation of deepwater production risers.