Oil bank

Since Thin Film Spreading Agents do not produce ultralow interfacial tensions, capillary forces can trap oil in pore bodies even though the oil has been displaced from the surface of the porous medium. Therefore, recovery of incremental oil is dependent on the formation of an oil bank. Muggee, F. D. U.S. Patent 3 396 792, 1968. 

Bank the concentration of oil (oil bank) in a reservoir that moves cohesively through the reservoir. 

Figure 11.6 Illustration offlowing oil ganglia, in water-wet porous media, coalescing to form a continuous oil bank.

Similarly, supplementing soy oil (90% Cis) increased the total Qg of milk fat from 25% to 60% of milk fatty acids. Yields of Q, to C14 were reduced by both supplements, whereas the yield of Ci6 o was increased by palm oil and reduced by soya oil (Banks et al., 1976) these effects are typical (Noble et al., 1969). Similarly, supplementing increasing amounts of coconut oil (high in Ci2 o and Ci4 o) increased the proportions of these in milk fat and reduced the proportions and yields of short-chain fatty acids and Ci6 o (Storry et al., 1971). 

One interesting consequence of the results described above is that the oil phase should be discontinuous in the portion of an oil bank where Ca is high during an enhanced recovery process such as... 

IMMISCIBLE CO2/OIL. SET NO. 2. EXPERIMENT NO. 3. This experiment should be compared with experiment No. 1. The CT scans showed a sharp, nearly vertical, CO2 front without viscous fingering. Figures 14a-d. The CO2 entered the core in the upper half of the inflow face and then swept down, forming a small layover angle. A C02-free oil bank developed during the flood but was overtaken by the faster moving CO2. CO2 and oil production were simultaneous at the outflow end of the core. 

IMMISCIBLE CO2/QIL WITH LOWERED CO /BRINE IFT. SET NO. 2. EXPT. NO. 4. The core used in experiment No. 3 was restored to water flood residual oil saturation and flooded with 0.05 wt% AEGS 25-12 surfactant in brine, and then CO2. Initially, the CO2 began to sweep the entire core cross section and build an oil bank similar to the one observed in experiment No. 3. Then the CO2 buoyed up and overrode the water and oil banks. Figures 15a-d. The result is both poor sweep and poor displacement of oil. 

The beneficial surfactant effects observed during miscible CO2 flooding did not extend to the case when the oil and CO2 are immiscible. A viscous foam did not form or propagate, and the reduced capillary pressure due to surfactant IFT lowering allowed the CO2 to override the brine and oil banks. 

No sign of an oil bank was detected at the observation well. Before the test began, the average oil saturation in this well had been 19% in the lower 20 ft of the formation and just 4% in the upper 10 ft. 

Low interfacial viscosity is desirable in enhanced oil recovery operations, so that displaced oil globules may readily coalesce into an oil bank. Emulsion stability decreases as interfacial viscosity decreases, and this condition increases the ease with which an oil bank can be formed. Wasan et al. (J5) found a qualitative correlation between coalescence rates and interfacial viscosities for crude oil. 

Oil Bank Formation. If a surfactant or surfactant-forming material is injected into a reservoir and mobilizes residual oil, then oil recovery is more efficient if the mobilized oil droplets can coalesce to form an oil bank. 

The oil bank that forms will exist at an oil saturation that is greater than the residual oil saturation. At the front of the bank, residual oil is taken up, while at the back, the capillary number must remain high to minimize oil entrapment. In this way, the oil bank grows larger and forms slightly ahead of the injected chemicals. 

The formation and displacement of the oil bank depends upon the nature of the phases formed in the porous medium and their relative permeabilities, which may also change as a result of changes in wettability. Detailed discussion of these factors is beyond the scope of this chapter Chapter 6 and references 37 and 38 address this topic. 

It was observed that the formulations consisting of ethoxylated sulfonates and petroleum sulfonates are relatively insensitive to divalent cations. The results show that a minimum in coalescence rate, interfacial tension, surfactant loss, apparent viscosity and a maximum in oil recovery are observed at the optimal salinity of the system. The flattening rate of an oil drop in a surfactant formulation increases strikingly in the presence of alcohol. It appears that the addition of alcohol promotes the mass transfer of surfactant from the aqueous phase to the interface. The addition of alcohol also promotes the coalescence of oil drops, presumably due to a decrease in the interfacial viscosity. Some novel concepts such as surfactant-polymer incompatibility, injection of an oil bank and demulsification to promote oil recovery have been discussed for surfactant flooding processes. 

DISPLACED OIL GANGLIA MUST COALESCE TO FORM A CONTINUOUS OIL BANK -. FOR THIS A VERY LOW INTERFACIAL VISCOSITY IS DESIRABLE... 

Figure 2. Schematic presentation of the role of coalescence of oil ganglia in the formation of the oil bank.

Transient Processes. There are several transient processes such as formation and coalescence of oil drops as well as their flow through porous media, that are likely to occur during the flooding process. Figure 12 shows the coalescence or phase separation time for hand-shaken and sonicated macroemulsions as a function of salinity. It is evident ithat a minimum in phase separation time or the fastest coalescence rate occurs at the optimal salinity (53). The rapid coalescence could contribute significantly to the formation of an oil bank from the mobilized oil ganglia. This also suggests that at the optimal salinity of the system, the interfacial viscosity must be very low to promote the rapid coalescence. 

In oil recovery processes, the formation of an oil bank is very important for an efficient oil displacement process in porous media. This was established from studies on the injection of an artificial oil bank followed by the surfactant formulation which can produce ultralow interfacial tension with the injected oil. We observed that the oil recovery increased considerably and the residual oil saturation decreased with the injection of an oil bank as compared to the same studies carried out in the absence of an injected oil bank (54). Figure 17 schematically represents the oil bank formation and its propagation in porous media, which is analogous to the snowball effect. If an early oil bank is formed then it moves through the porous medium accumulating additional oil ganglia resulting in an excellent oil recovery, whereas a late oil bank formation will result in a poor oil recovery. 

Figure 17. Schematic illustration of the injection of an oil bank and the subsequent "snowball effect" in enhanced oil recovery.

When Swi is less than Swf, the oil bank fonns inunediately and overtakes Swf. Then the nniform water satnration, 8 1, is formed (Green and WiUhite, 1998). Figure 2.20 shows the satnration profile in this situation. Water breaks through at... 

The boundary between the denuded water and the initial water moves at Vwb defined in Eq. 2.120. The front of the oil bank moves at Vobi... 

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