DISPLACEMENT OF HEAVY OIL BY CARBON DIOXIDE IN A TUBE

Abstract

After using primary and secondary oil recovery methods, about two third of the original oil in
place is left behind in the reservoir. Enhanced Oil Recovery (EOR) methods are being used to recover that oil.
Carbon dioxide (CO2) flooding is one of the enhanced oil recovery (EOR) methods that is used to recover the
oil. The interest here lies in recovery of heavy crude oil in a capillary tube with a radius of micrometer scale
and that oil is displaced by carbon dioxide (CO2). The dissolution of CO2 in oil reduces oil viscosity and swells
it, making it easier to displace the oil. In immiscible displacement of viscous liquid (heavy crude oil) in a tube
by a gas with lower viscosity than the liquid (Carbon dioxide CO2), a gas bubble moves steadily and leaves
behind a thin liquid film of thickness h∞, which is known as the Bretherton problem.
ANSYS® FLUENT software is used to solve the problem of CO2 displacing heavy oil in a tube. Different velocities, capillary numbers (Ca) and different tube radii are used as an input into ANSYS® FLUENT software
to solve different cases. The oil film thickness that left behind (h∞) is reported both without mass transfer and
with mass transfer.
The oil film thickness that is left behind, h∞ (in the case of fluid mechanics) is decreased when capillary
number/bubble velocity is decreased. That was the case for all different radii and different velocity inputs.
When there is no mass transfer, the non-dimensional film thickness left behind h∞/R plotted against capillary
number fits Bretherton line. With a small capillary number and a radius of 1µm, the shape of the profile
of the CO2 bubble is a hemisphere and the oil film thickness that is left behind (h∞) is very small. At large
capillary number (10-1 for R= 1µm) and small radius (0.1µm), the profile shape of the CO2 bubble is pointed.
At the center-line of the tube there is no pressure drop in the gas phase nor in the liquid phase, however, most
the pressure drop takes place across the interface. Even under mass transfer of CO2 into oil, bubbles show
Bretherton-type behavior. The thickness of thin residual oil film decreases in the presence of mass transfer,
leading to an increase in oil recovery. In addition, the oil film thickness that is left behind (h∞) with mass
transfer is less than the oil film left behind without mass transfer. Convection in this case opposes the mass
transfer and limits how much CO2 can dissolve in oil.