Author(s)

Diana González, Milan Stanko, Michael Golan

Department of Geoscience and Petroleum—NTNU, Trondheim, Norway.

This work is a thermo-fluid numerical case study to investigate the size and performance of a system that eliminates needs for insulating, heating and inhibiting chemically the deposition of wax in subsea tie-in flowlines. For short, we call this type of systems “Cold Flow”. The particular system analyzed in this study consists of a reactor unit at the inlet to the flowline, where the thermal solubility of the wax-creating molecules is reduced by cooling. Subsequently, solid wax is deposited in the reactor piping and wax free crude is entering the flowline. The reactor is regenerated periodically. The reactor-pipeline system was modelled using a commercial flowline simulator, with transient, thermal, multiphase and deposition capabilities. The basic layout used was a transportation pipeline of 8 km and 6.69 in ID with a mass flow rate of 17.51 kg/s, a water cut (WC) of zero and an inlet temperature of 70°C. The wax appearance temperature (cloud point) of the crude is 22°C and the seabed temperature is 4°C. Three types of reactors have been simulated: a non-insulated pipe section, a passive cooler with a bundle of parallel pipes and an active cooler. Sensitivity analyses have been performed for all three cases varying the external convective coefficient, the reactor pipeline diameter and the WC. For a non-insulated pipeline section cooler, the required length is of the same order of magnitude as the main flowline, implying that such a solution is impractical for short flowline distances or when a compact deployment is desired. For the passive cooler case, the required length was half of that in the previous case; thus it is still significant. For the active cooler reactor, the required cooling duty was 2.2 MW. In all three cases, the pipe-flow dynamics were analyzed, and the pigging arrangement complexity has been qualitatively addressed. However, the detailed design falls out of the scope of this study.

Cold Flow, Wax Deposition, Flow Assurance, Wax Modelling, 1D Simulation

González, D. , Stanko, M. and Golan, M. (2018) Numerical Feasibility Study of a Wax Cold Flow Approach for Subsea Tie-In Flowlines Using a 1D Mechanistic Multiphase Flow Simulator. Engineering, 10, 109-123. doi: 10.4236/eng.2018.103008.