News & Events
- July 15th, 2008Flowasta released
Contact Area
The transport of hydrate forming components from the hydrocarbon phases to the water phase, where hydrate formation takes place, is proportional to the contact area between the hydrocarbon and aqueous sub-systems. The contact area depends on flow regime, viscosities and flowrate.
Oil-Water
Oil and water are in terms of transport treated as a single phase of either water suspended in oil or oil suspended in water. The suspension shifts from “water in oil” to “oil in water” at the inversion point, which in Flowasta is assumed to happen for a water volume percent of 70. The average bubble diameter of the suspended phase is assumed to be 2.2 times smaller than the maximum bubble diameter found from the correlation by Razzaque et al. (2003) and Hesketh et al. (1987)
Dpipe is the pipe diameter and σ is the interfacial tension between the dispersed (d) and continuous (c) phases. ρ is the density, μ the dynamic viscosity and U is the average velocity. The critical Weber number (Wecr) is assumed equal to 1.1 (Hesketh et al., 1987).
The number of bubbles of the suspended phase is calculated assuming all bubbles have the average diameter. The oil-water contact area in a pipeline section is then number of bubbles contained in section times the surface area of a single bubble.
Gas-Water
For a stratified flow the contact area is derived from the height of water in the pipe determined from the water hold-up.
For annular flow the contact area equals the area inside the annulus, which area is determined by the water hold-up.
The contact area for water-gas bubble flow (gas bubbles suspended in water) is calculated in the same way as for water in oil suspensions.
Slug flow is assumed to be made up of a section with stratified flow and a liquid (slug) section with gas bubbles. The length of the slug is determined from the pipe diameter while the gas volume in the slug equals the volume not taken up by liquid, which volume is found from a slug hold-up correlation (Orell, 2005). Volume balances determine the length of the stratified region and the liquid hold-up in the stratified region.
Gas-Oil-Water
For a pipeline transporting gas, oil and water the gas-water contact area is calculated as for gas-water flow, but corrected for the volume fraction of water in oil. The oil-water contact area is calculated as for oil–water flow while taking into consideration that the pipe is only partly filled with liquid.
