Wettability and Spreading: Two key Parameters in Oil Recovery With Three-Phase Gravity Drainage
- Olga Vizika (Inst. Francais du Petrole) | J-M. Lombard (Inst. Francais du Petrole)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- February 1996
- Document Type
- Journal Paper
- 54 - 60
- 1996. Society of Petroleum Engineers
- 4.3.4 Scale, 5.4.2 Gas Injection Methods, 4.1.5 Processing Equipment, 5.7.2 Recovery Factors, 5.2.1 Phase Behavior and PVT Measurements, 6.5.2 Water use, produced water discharge and disposal, 5.3.4 Reduction of Residual Oil Saturation, 5.5.8 History Matching, 5.5 Reservoir Simulation, 5.4.1 Waterflooding, 4.1.2 Separation and Treating, 2.4.3 Sand/Solids Control
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The objective of this paper is to show that the porous medium wettability and the spreading characteristics of the fluid system hold the key roles in three-phase gas injection, and to study to which extent these two parameters affect oil recovery and phase distributions. To this end gravity assisted inert gas injection experiments have been performed in water-wet, oil-wet and mixed-wet porous media for spreading and non-spreading conditions. The experiments are simulated and the oil and gas relative permeabilities for three-phase flow are calculated by history matching. It is proved that the existence of wetting and spreading oil films - caused by wettability and spreading - greatly affects the flow mechanisms and consequently the recovery kinetics and the process efficiency. The results are interpreted in terms of basic physicochemical parameters on the basis of pore scale mechanisms.
Gas injection is increasingly being considered as a very efficient oil recovery process especially when it is assisted by gravity forces. Gravity drainage has been observed to lead to low oil saturations in thick, steeply dipping reservoirs with high permeability.
Early theoretical and experimental studies have analysed the gravity drainage of a liquid out of a sand column (recovery rate, saturation distribution as a function of time) and good agreement between experiment and theory has been reported. A little later an important effort has been made to take into account flow by film that must become important for low liquid saturations. However all these studies are limited to the drainage of oil without the presence of any water. Besides, history matching has given good results for some fields while for others the predictions were less successful.
For the first time in the early seventies the role of connate water in gravity drainage has been stressed. The concept of spreading of oil on water in presence of gas, that would enable flow of oil by film, has been used to explain the very low saturations obtained by gravity drainage in highly permeable sand columns. It is claimed that high recovery efficiency is obtained even for non-spreading conditions, however little information is given on the physicochemical properties of the fluids used.
Later, relative permeability studies showed that gravity drainage can be very efficient in water-wet, connate-water-bearing reservoirs.
More recently the effect of spreading and the role of flow by film in gravity drainage has been revisited and the experiments in consolidated and unconsolidated cores have been supported by visualizations in 2-D micromodels. It has been observed that spreading conditions in water-wet porous media favor the formation of oil films and lead to very low oil saturations.
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