Effects of buoyancy forces on immiscible oil/water displacements in porous media.

• Main Author: Thirunavu, Subramanian.
• Other Authors: Neale, Graham
• Format: Others
• Published: University of Ottawa (Canada) 2009
• Subjects: Applied Mechanics.
• Online Access: http://hdl.handle.net/10393/10231; http://dx.doi.org/10.20381/ruor-8189

The effects of buoyancy forces on liquid-liquid displacement processes occurring in porous media are important in a variety of practical situations, in particular during the displacement of oil from partially-depleted underground reservoirs by means of aqueous solutions. Most previous studies involving the visualization of water/oil displacements in porous media have been undertaken in horizontal two-dimensional porous medium cells. The objective of this work was to determine the effects of buoyancy forces on the fingering pattern and oil recovery by conducting immiscible displacement experiments in two-dimensional porous medium cells aligned in the vertical plane. A consolidated porous medium cell was utilized to perform the displacements, which permitted a wide range of experiments to be carried out within an identical porous medium. In order to obtain a clear understanding of the effects of buoyancy forces (both favourable and unfavourable) experiments were carried out in three different modes, namely horizontal, vertical upward, and vertical downward. As the effects of buoyancy forces are almost negligible, in the horizontal mode, recoveries obtained in this mode are used as a reference and compared to those obtained in the other two modes. For the system studied in this work, as the displacing liquid in all cases had a higher density than the displaced liquid, buoyancy forces were always favourable in the vertical upward mode and always unfavourable in the vertical downward mode. The immiscible system employed consisted of heavy paraffin oil and glycerol solution as the displaced and displacing phases respectively. The viscosity ratio was varied by changing the concentration of the glycerol solution. Displacements with five different viscosity ratios were studied. Breakthrough time was measured and fractional oil recovery was calculated. The effects of buoyancy, viscous and capillary forces as well as the injection flow rate were also observed. The results obtained indicate that the buoyancy forces are highly effective at very low flow rates and low viscosity ratios (or high density ratios), and even with a slight increase in the flow rate, buoyancy forces lose their importance quickly.