Investigation of the Effect of Sand on Annular Flow Behaviour in Horizontal Pipes

Annular flow is encountered in petroleum production systems, where reservoir fluids are conveyed to surface via wells and transport lines and also nuclear power plants, chemical and refining processes (e.g. reactors, heat exchangers). In this type of flow regime, the gas, together with the entrained liquid droplets, flows within the core of the pipe at high velocities, while the liquid flows as a film along the pipe walls. Experimental investigations on annular flow behaviour, sand transport and its effect on annular flow in horizontal pipe are presented, with the aim of progressing the understanding of such flow and facilitate the optimum design of hydrocarbon production systems. The experiments were conducted using a closed-loop horizontal pipe with an internal diameter of 2-inch (0.0504m). The experiments could be categorized into: water/air flow, water/sand flow, water/air/sand annular flow and sand sampling. The water/air flow experiments could be subdivided into water/air flow (Plug, Slug, Stratified-smooth and stratified-wavy flows) and water/air annular flow. The results of water/air flow were plotted on flow regime map to aid the recognition of the different flow regimes. For the water/air annular flow experiments, key flow features are presented, with discussion on liquid hold up, film thickness, wave frequency and pressure gradient. The water/sand flow experiments investigated sand saltation, sand streaks, moving dunes and sand beds. Also, sand particles of 212microns and 500microns for water/air/sand annular flow were investigated. Similarly, sand sampling experiments were also carried out. The OLGA dynamic multiphase flow simulator was run against the experimental results. The OLGA simulations of the water/air annular flow shows a better liquid hold-up match at lower superficial liquid velocities. For sand transport, OLGA also identified sand flow in annular flow as no bed. The main contributions of this study are: presenting the minimum transport velocities for water/sand flow in horizontal pipe. For water/air annular flow, the contributions are: detailed annular flow behaviours in horizontal pipes with annular-wavy slug flow at low superficial liquid and gas velocities, and full symmetrical annular flow from superficial gas velocity of 12m/s at low Vsl. The study proves that superficial liquid velocity has impact and significance on wave frequency: This has refuted Setyawan et al., (2014), whose report presented superficial liquid velocity to be insignificant in wave frequency. The study also identified that the higher the Vsl, the higher the interfacial shear stress but the lower the wave velocity. Also, the higher the Vsl, the higher interfacial friction factor/shear stress, but the lower the wave frequency. For water/air/sand annular flow, this study identifies saltation and suspension as the two main sand distribution in annular flow, with small-size particles being transported at the gas core and the bigger particles at the bottom (i.e. in the liquid film) along in the horizontal pipes. Finally, sand particles’ size does not appear to have an impact on wave velocity and wall shear stress, while sand concentration affects wall shear stress, but not wave velocity. Lastly, presence of sand particles in the liquid film is associated with increase in wave amplitude in annular flow, as more energy is being dissipated from the gas phase to keep the waves in motion.