Mobility ratio favorable

Chromatographic separations are accomplished by continuously passing one sample-free phase, called a mobile phase, over a second sample-free phase that remains fixed, or stationary. The sample is injected, or placed, into the mobile phase. As it moves with the mobile phase, the sample s components partition themselves between the mobile and stationary phases. Those components whose distribution ratio favors the stationary phase require a longer time to pass through the system. Given sufficient time, and sufficient stationary and mobile phase, solutes with similar distribution ratios can be separated. 

Thus far all the separations we have considered involve a mobile phase and a stationary phase. Separation of a complex mixture of analytes occurs because each analyte has a different ability to partition between the two phases. An analyte whose distribution ratio favors the stationary phase is retained on the column for a longer time, thereby eluting with a longer retention time. Although the methods described in the preceding sections involve different types of stationary and mobile phases, all are forms of chromatography. 

While water-soluble polymers can be used to achieve a favorable mobility waterflood for low to modestly viscous oils, usually toe process cannot economically be apphed to achieving a favorable mobility displacement of more viscous oils—those having viscosities of from approximately 100 cP or higher. These oils are so viscous that the amount of polymer needed to achieve a favorable mobility ratio would usually... 

CZE is high voltage, free-solution electrophoresis carried out in a capillary. The capillary is filled with the running electrolyte (a buffer solution), and the ionic analytes are separated on the basis of the differences in their electrophoretic mobilities. The favorable ratio of surface area to volume allows the dissipation of the Joule heat from the capillary and the application of high electric fields with rapid and efficient separations. Also, the anticonvective characteristic of the capillary limits the process of zone diffusion, maintaining the efficiency of separation without the need of further anticonvective media such as gels. 

The inherently unstable nature of miscible displacements with unfavorable mobility ratios (the viscosity of the displacing fluid is less than the viscosity of the displaced fluid) and unfavorable density ratios (for a downward vertical displacement, the density of the displacing fluid is greater than the density of the displaced fluid) has been well documented (6-18). For a downward vertical displacement with a favorable mobility ratio and an unfavorable density ratio. Hill ( ) proposed an approximate theory that... 

We found that the displacement is stable, when both the mobility ratio and the density ratio are favorable. 

When the mobility ratio is unfavorable and the density ratio is favorable, we can define a critical velocity vj below which a displacement is stable. In the case that the mobility ratio is favorable and the density ratio is unfavorable, the displacement is... 

Fiori and Farouq Ali (73) proposed the emulsion flooding of heavy-oil reservoirs as a secondary recovery technique. This process is of interest for Saskatchewan heavy-oil reservoirs, where primary recovery is typically 2-8%. Water-flooding in these fields produces only an additional 2-5% of the original oil in place because of the highly viscous nature of the oil. In laboratory experiments, a water-in-oil emulsion of the produced oil is created by using a sodium hydroxide solution. The viscous emulsion formed is injected into the reservoir. Its high viscosity provides a more favorable mobility ratio and results in improved sweep of the reservoir. Important parameters include emulsion stability and control of emulsion viscosity. 

The conventional mobility ratio in multiphase flow is defined as the displacing fluid mobility divided by the total mobility of displaced water and oil phases. From the previous section, we can see that the unit mobility ratio based on the conventional definition is not a valid criterion to distinguish favorable and unfavorable mobility control conditions. We have found that a better criterion should be the unit mobility ratio, which is defined as the displacing fluid mobility divided by the oil mobility multiplied by the oil saturation (Eq. 4.9). In this section, we attempt to justify the proposed idea from the stability of displacement front. 

A high viscous ASP system should help oil displacement. Then often this question is raised why do we need a low interface viscosity (short equilibrium time) A high viscous ASP system helps oil displacement because of more favorable mobility ratio. The oil displacement is macroscopic. In a chemical flood process, the isolated oil drops need to coalescence to form an oil bank. A low interface viscosity between the oil drop and the displacing ASP fluid will ease such a coalescence process, and this process is microscopic. Therefore, we need a low interfacial viscosity to build up an oil bank and a high viscous ASP fluid to displace the oil bank ahead. 

Unless mass transfer is fast compared with reaction, it can affect selectivity in reactions in which a reactant enters from, or a product exits into, another phase. Products with greater mobility, or formed from reactants with greater mobility, are favored. If several reactants of a single reaction enter from another phase, their ratios shift in favor of the more mobile ones, possibly causing a corresponding selectivity shift. 

Consider the effect of adding sufficient polymer to the injected water so that the apparent viscosity of the polymer solution is 4 cp. Assume that no reduction in water relative permeability is caused by the polymer. The mobility ratio, Mg, would be expected to decrease by a factor of four to about 0.54, which is clearly favorable. In Example 3.5, the displacement performance of a polymer flood was estimated for a polymer solution containing 300 ppm polymer with an apparent viscosity of 4.0 cp. Retention is 17.5 /tg/g at 300 ppm, so that Dp =0.424. Effective inaccessible PV for this system is estimated to be 0.25. Thus, —< g+Z>p =0.174. 

Waterflooding was initiated in 1964 in the Ranger zone area that was later to be polymer flooded. Response to the waterflood was generally favorable, but WOR s showed a steady increase. The waterflood mobility ratio was about 14, indicating that improved sweep efficiency might be expected from polymer flooding. Tests with a polyacrylamide indicated that the mobility ratio could be reduced to just slightly above 1.0 with a polymer concentration of 250 ppm. Resistance factor measured in the laboratory was 10.7, and polymer adsorption was measured and predicted to be 85 Ibm polymer/acre-ft. 

A 1.35-cp polymer solution was injected continuously over a period of 33 months into the four-spot polymer pilot. The presence of the polymer solution, which exhibited a resistance factor of 8 in this reservoir rock, converted this flood to a favorable mobility ratio of 6. The water-cut performance of this pilot is shown in Fig. 8,... 

The objective of polymer flooding would be to improve the displacement efficiency by lowering the mobility of the displacing fluid. No significant increase in oil recovery was expected as a result of an increase in volumetric sweep efficiency. At Frannie, the water-flood has an unfavorable mobility ratio (A/< 1 is favorable), and the viscosity ratio of the oil (15 cp [15 mPa-s]) to injected water (0.77 cp [0.77 mPa- s]) is about 19. If the viscosity of the injected fluid were increased to equal the oil viscosity (/ n// <, l)> "lO bility ratio would improve dramatically. The change in mobility ratio could produce an estimated 5 million STB [795 X10 m ] of oil (2% of the OOIP) according to the fractional flow prediction. 

For the 750 ppm solution, the simulator used a resistance factor of 28.63 to yield a 22.0 cp apparent polymer viscosity for the prediction of the flood performance. This concentration yielded a favorable mobility ratio of 0.26 at residual oil saturation. The simulator predicted that the polymer flood would recover 3,042 MBO or 8.0 percent... 

By injecting a viscous polymer solution, the mobihty ratio was decreased and made favorable. The viscosity of the injected polymer solution was typically 35 to 40 cp. If polymer degradation was not significant, this level of viscosity decreased the mobihty ratio from 9.4 to approximately 0.3. When fluids can freely cross flow between strata, the rate of movement of a polymer front is independent of permeability, so long as the reciprocal of the mobility ratio is greater than the permeability ratio between the strata (Sorbie and Seright 1992, Wang et al. 2008). 

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