Mobilization of Residual Oil Under Equilibrium and Nonequilibrium Conditions
- Andrew C. Lam (U. of Texas) | Robert S. Schechter (U. of Texas) | William H. Wade (U. of Texas)
- Document ID
- Society of Petroleum Engineers
- Society of Petroleum Engineers Journal
- Publication Date
- October 1983
- Document Type
- Journal Paper
- 781 - 790
- 1983. Society of Petroleum Engineers
- 5.6.5 Tracers, 4.3.4 Scale, 1.2.3 Rock properties, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 2.5.2 Fracturing Materials (Fluids, Proppant)
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A microvisual study of residual oil mobilization that uses a relatively simple chemical system consisting of water, n-propanol, and cyclohexane is presented. Two different classes of experiments were performed to determine the sensitivity of the capillary number required to displace a particular residual oil globule from chemical equilibrium. It was found that under certain circumstances the capillary number required to mobilize the oil drop could be reduced greatly if the displacing phase contained more alcohol than it would in equilibrium with the trapped phase.
Experiments clearly demonstrated that spontaneous emulsification by a diffusion and stranding mechanism could not account for the differences between equilibrium and nonequilibrium capillary numbers. Experimental observations did correlate well with the development of interfacial turbulence (Marangoni effect). Variations that, according to theory, tended to enhance the level of interfacial turbulence between the equilibrium and nonequilibrium capillary numbers were observed. The importance of the Marangoni effect relative to laboratory oil recovery experiments is discussed.
A second class of experiments consisted of observing,, the displacement of residual oil globules that had been increased in volume (swollen) by mass transfer from a continuous phase flowing too slowly to displace the drop. Once the residual oil globule attained equilibrium with the continuous phase, the flooding velocity was increased until the swollen globule was displaced. Surpassingly, slightly swollen globules required a larger capillary, number for [mobilization than the original drop. Thus. the capillary number for swollen residual oil globules goes through a maximum as a function of the degree of volume increase. The precise position of the maximum varies for each globule since mobilization is a complex function of geometry.
The mobilization of residual oil globules by contact with a flowing surfactant-rich solution (microemulsion) is a complex process not fully understood. Most of the complexities arise because the trapped phase and the surfactant solution are not in chemical equilibrium and there is mass transfer from one phase to the other. If the two phases are in equilibrium, then the mechanism ofmobilization appears to be satisfactorily established. An oil globule is displaced when the interfacial tension (IFT) is reduced to an extent that the pressure gradient created by the motion of the continuous phase is sufficient to overcome the capillary forces holding., the globule in place. Several experimental studies have been reported and the concept of a critical capillary number has evolved.
The reduction of IFT is considered to be an important factor in the selection of a suitable solution for oil recovery.
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