Mechanistic models that identify flow regimes and predict pressure drop in two-phase, gas-liquid flows are widely used in flow assurance calculations during production and pipeline transport. Regime transitions are influenced by gas and liquid properties, which are functions of temperature, pressure, and composition. In some situations, production fluids experience large temperature variations, particularly if the well must be shut in or the pipeline flow suspended. The impact of these temperature variations on the onset of flow regime transitions is explored over ranges typical of production and pipeline transport.
A two-phase, gas-liquid mechanistic model has been implemented for all pipe inclination angles, based on the Barnea (1987) unified model, with both historically relevant and more recent closure relations considered (Shoham 2006; Gomez et al. 2000). Several terms in the mechanistic models that were previously simplified for cases with very different liquid and gas properties have been recovered. This generalization extends the model to applications where the densities and viscosities of the gas and liquid can be very similar, making it valid over broad ranges of temperature and pressure. In less extreme cases, the model has been validated with experimental and field data. The paper shows the impact on regime transitions and pressure drop calculations in both typical and extreme cases, including deepwater production and pipeline transport under harsh winter conditions.
Temperature has several major impacts on the regime and pressure drop in multiphase gas-liquid flows. Regime transitions are particularly impacted in deepwater wells, where much of the vertical lift portion is submerged in seawater at temperatures as cold as 4°C. Similarly, pipelines at extreme latitudes experience very cold winters. In addition to impacting the equilibrium flow regime, the frictional pressure drop is significantly modified for most regimes if production fluids are dramatically cooled as a result of the associated increase in liquid viscosity.
Regime transitions in seafloor pipelines, jumpers, and vertical lift production tubing are modified by the significant heat transfer to the low temperature seawater. For producing wells, flow in collection lines is impacted, shifting the transitions from slug to churn flow and from churn to annular flow. In vertical lift sections the release of gas from liquids at the bubble point caused by extreme deepwater heat transfer can be moved significantly upstream or downstream in the wellbore. This moves the onset of regime transitions for bubbly and dispersed bubble flow for oil producing wells containing dissolved gas. This is especially true when the pressure drops below the bubble point pressure along a section of tubing exposed to temperatures common in deep water. Subsequent transitions to slug and then churn flow are offset proportionally because of the shift in onset of bubbly or dispersed bubble flow.
In near horizontal pipelines, the transition from stratified smooth to stratified wavy flow is modified through the influence of temperature on viscosity. This is significant for corrosion issues, where stratified wavy flow is preferred over stratified smooth flow. Simultaneously, the impact on viscosity has a large influence on the pressure drop.
Barnea, D., 1987. A unified model for predicting flow-pattern transitions for the whole range of pipe inclinations, Int. J. Multiphase Flow, 13 (1): 1-12.
Gomez, L.E., Shoham, O., Zelimir, S., Chokshi, R.N., and Northug, T., 2000. Unified mechanistic model for steady-state two-phase flow: Horizontal to vertical upward flow, SPE Journal, 5 (3): 339-350.
Shoham, O. 2006. Mechanistic Modeling of Gas-Liquid Two-Phase Flow in Pipes, first edition. Dallas, Texas: Society of Petroleum Engineers.
See more of this Group/Topical: Topical 9: 4th International Conference on Upstream Engineering and Flow Assurance