Flooding Foam fractionation

In Figure 8, the experimental results from the (4 m/day frontal advance rate, oil free) short core flood are compared to the simulated pressure drops which were based on the limiting capillary pressure principle. In this particular case was chosen at 0.35 over a range of water fractional flows from 0.01 to 0.15 to closely match the experimental data. For Sw > a fractional flow curve was chosen which matched the experimental data closely by appropriately adjusting the gas phase relative permeability curve. The water relative permeability curve remains the same as defined in the Appendix under gas/water relative permeabilities. The composite foam fractional flow curve can be seen in Figure 9. Notice the vertical section in the curve for the foam flow case lies at = 0.35. 

Extensive mobility control applications of foams are limited by inadequate knowledge of foam displacement in porous media, plus uncertainties in the control of foam injection. Because of the importance of in situ foam texture (bubble size, bubble size distribution, bubble train length, etc.), conventional fractional flow approaches where the phase mobilities are represented in terms of phase saturations are not sufficient. As yet, an adequate description of foam displacement mechanisms and behavior is lacking, as well as a basis for understanding the various, often contradictory, macroscopic core flood observations. 

In the case of the water-wet foam floods, the carbon dioxide solubility which gave the best match to the secondary floods was 0.8 mol fraction, while a value of 0.7 gave the best match for the tertiary foam floods, as shown in Figures and 8. The best values for the oil-wet case were O.9 mol fraction for both the secondary and tertiary cases, as shown in Figures 9 and 10. 

Sieve trays with 10% hole area and 0.5 cm diameter holes will be used. Trays are available in standard diameters of 0.25 m increments (0.25,0.50, 0.75, 1, 1.25, 1.50,. .., m). Based on the top tray conditions, determine the required tray diameter rounded up to the nearest larger standard size. Assume a tray spacing of 0.5 m, a foaming factor of 0.80, and a fraction of flood of 0.80. The liquid density is given as 730 kg/m and the vapor density may be estimated based on the ideal gas equation. The liquid surface tension is 27 dynes/cm. 

The column has 3 m diameter sieve trays with 0.5 cm diameter holes and 10% hole area. The tray spacing is 45 cm. Assuming a foaming factor of 0.85, calculate the vapor flood velocity at the top tray. Check if the column diameter is acceptable. The fraction of flood velocity should be within a 60-85% range. 

Tray type Weir height Weir length Downcomer clearance Tray spacing Foaming factor Fraction of flood Surface tension Liquid viscosity... 

Sieve trays will be used with 60 cm spacing, 6 cm weir height, 0.6 cm hole diameter, 0.25 cm tray thickness, 5 cm downcomer clearance, and hole area 10% of the total tray area. The foaming factor is 0.80 and the froth density in the downcomer is 0.5. The target fraction of flood velocity is 0.70. 

Second, after foam flooding cores, Bernard et al. (32) flushed with water or brine to estimate trapped-gas saturation. They assumed that water or brine filled the pore space through which gas flowed but did not substantially alter the fraction of gas trapped. Their trapped saturations ranged from 10 to 70% depending upon the surfactant type and the presence of oil in the porous medium during the foam flood. Such measured saturations apply only to trapped gas following a waterflood, and not to dynamic or steady-state foam flooding. 

This chapter will focus on the stability of foams flowing in porous media when in the presence of crude oil. Many laboratory investigations of foam-flooding have been carried out in the absence of oil, but comparatively few have been carried out in the presence of oil. For a field application, where the residual oil saturation may vary from as low as 0 to as high as 40% depending on the recovery method applied, any effect of the oil on foam stability becomes a crucial matter. The discussion in Chapter 2 showed how important the volume fraction of oil present can be to bulk foam stability. A recent field-scale simulation study of the effect of oil sensitivity on steam-foam flood performance concluded that the magnitude of the residual oil saturation was a very significant factor for the success of a full-scale steam-foam process (14). 

If a C02 flood is already underway, then the initiation of C02-foam mobility control will cause changes in the injection schedule. Because in many cases C02 is the major adjustable operating expense, this alone may call for an increase in rate of outlay. On the other hand, industry experience has shown that other things being equal, the rate of oil production is proportional to the rate of injection of C02, which would be greater by a factor of 2—3 in a high-C02-fraction foam flood over a 2 1 WAG flood. Consequently, this cost increase can be expected to be matched quickly by increasing production. 

Foaming in fractionation and absorption columns can drastically lower capacity and lead to premature flooding, liquid carryover, and solvent losses. In packed columns, foaming can also lead to poor distributor and redistributor action. 

It can be anticipated that all gas-flood projects, as they are presently being carried out, will leave a large fraction of the reservoir oil uncontacted by the injected fluids. This bypassed oil will remain inplace, undisplaced by the injected fluid. Thus, in each current field project, the amount of incremental oil produced by gas flooding could be substantially increased if the uncontacted oil could be reached. The improvement of the vertical and areal distribution of injected fluids through-out the reservoir requires much better methods of sweep and mobility control. The utility of the foams, in general, as mobility control agents has not been extensively tested. In principle they offer a spectrum of fluid mobility behaviour depending on the in-situ foam phase stability. 

Use one pass, tray spacing (0.6096 m), minimum downcomer area (0.10), foaming factor (1), and over design factor (1). Set the fractional approach to flooding at 0.7. Use the Fair design method for flooding.]... 

The flood history is summarized in Table 3. First baseline pressure drops were determined across the 1.8 m core during simultaneous injection of brine (without surfactant) and gas at a fixed frontal advance rate and varying gas fractional flows. A frontal advance rate of 4.0 m/day was selected to ensure a flow rate higher than the critical rate for effective foam formation and propagation. A non-adsorbing tracer, tritiated water, was added to the brine so that the breakthrough of the tracer could be compared with the breakthrough of the gas. 

Calculated mobility reduction factors are also shown in Figure 6. For the 60% foam quality case an experimental baseline pressure drop was not available, so we used the results of the modelling work described in a later section to estimate the pressure drop expected for gas/brine flow at the appropriate fractional flow. Since the 95% quality foam flood did not reach steady state foam flow conditions, and since the pressure drops in individual sections of the long core were influenced by the pressure drops due to foam flowing in downstream sections of the core, we cannot make exact comparison between the MRFs generated in the long core with... 

Foam Flooding. In enhanced oil recovery, the process in which a foam is made to flow through an underground reservoir. The foam, which may be either generated on the surface and injected or generated in situ, is used to increase the drive fluid viscosity and improve its sweep efficiency. In refinery distillation and fractionation towers, the occurrence of foams which can carry fiquid into regions of the towers intended for vapour. 

A common example of foam formation in the bottom of a fractionator inducing flooding occurs in a crude preflash tower. In this case, stable foam accumulates in the bottom of the column as a consequence of the "flow improver" chemicals added to crude oil. These chemicals reduce pressure drop in the crude pipelines. Once the foam level rises to the feed inlet nozzle, the trays flood and black distillate is produced. Please see Chapter 18 (Preflash Towers). 

Equation 1 above stales that a tray will become less efficient due to incipient jet flood when the pressure drop per tray, expressed in inches of liquid, equals 22% to 25% of the tray spacing. The inches of liquid term assumes the liquid is deaerated. Of course, the liquid in the downcomers and on the tray decks is closer to a froth than to a flat liquid. The more highly aerated the liquid is (i.e. the more foamlike it becomes), the greater will be the depth of liquid corresponding to a measured external pressure drop. Hence, liquids which foam in distillation columns (such as dirty amine and ethane-rich fractionators) reach their incipient jet flood point at pressure drops below the 20% indicated in Equation 1. 

Field observations reveal a common cause of premature flooding in hydrocarbon fractionation to be high foam levels generated in the bottom of towers served by circulating reboilers. These high levels cannot be observed in the ordinary manner and hence tend to elude detection. 

I explained that as we add more heat to the big can (more reboiler duty) and more capacity to the No. 1 coil (more condenser duty) that fractionation would get better. Better in the sense that the proof of the vodka would go up without reducing the production of vodka. Suppose, though, that the velocity of vapor leaving the big can becomes too great. We ve all seen what happens when we boil soup too quickly in a small pot. The pot foams or floods over onto the stove. We should have used a bigger pot or we should have kept the heat low on the stove. 

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