Oil recovery efficiency

The effect of temperature, pressure, and oil composition on oil recovery efficiency have all been the subjects of intensive study (241). Surfactant propagation is a critical factor in determining the EOR process economics (242). Surfactant retention owing to partitioning into residual cmde oil can be significant compared to adsorption and reduce surfactant propagation rate appreciably (243). 

Key mechanisms important for improved oil mobilization by microbial formulations have been identified, including wettability alteration, emulsification, oil solubilization, alteration in interfacial forces, lowering of mobility ratio, and permeability modification. Aggregation of the bacteria at the oil-water-rock interface may produce localized high concentrations of metabolic chemical products that result in oil mobilization. A decrease in relative permeability to water and an increase in relative permeability to oil was usually observed in microbial-flooded cores, causing an apparent curve shift toward a more water-wet condition. Cores preflushed with sodium bicarbonate showed increased oil-recovery efficiency [355]. 

The in situ combustion method of enhanced oil recovery through air injection (397,503,504) is an exceeding complex process chemically. However, because little work has been done on the effect of chemical additives to oil recovery efficiency, this process will not be discussed herein. 

Figure 7. Effect of Micellar Slug Size on the Oil Recovery Efficiency of Micellar Slug B4...

Slurry condition 1 density, 1.33 g/cm3 viscosity, 89 mPa- s Slurry condition 2 density, 1.20 g/cm3 viscosity, 3.2 mPa - s From the slurry introduction point, bitumen droplets must rise a distance of 0.80 m within the mean vessel residence time of 45 min in order to reach the froth layer and be recovered. What kind of oil recovery efficiencies would be predicted for each case ... 

Table I. IFT, Flattening Time and Oil Recovery Efficiency of 0.05% TRS 10-80 in 1% NaCl vs. n-Octane at 25°C...

In summary, several phenomena occurring at the optimal salinity in relation to enhanced oil recovery by macro- and microemulsion flooding are schematically shown in Figure 18. It is evident that the maximum in oil recovery efficiency correlates well with various transient and equilibrium properties of macro- and microemulsion systems. We have observed that the surfactant loss in porous media is minimum at the optimal salinity presumably due to the reduction in the entrapment process for the surfactant phase. Therefore, the maximum in oil recovery may be due to a combined effect of all these processes occurring at the optimal salinity. 

The key difference between the methods used for oil recovery from oil shales and that used for tar sands is in the methods used for separation of the organic constituent from the naturally occurring material. Oil shale processing requires the whole of the mined material to be heated to pyrolysis temperatures of 500°C or more, whereas the hot water process for tar sands extraction requires the mined tar sand (plus process water) to be heated to only around 70-80°C. Only the extracted bitumen from the tar sand, some 10-12% of the mined mass, has to be heated to ca. 500°C during the coking step to obtain synthetic crude. Because all the oil shale must be heated to pyrolysis temperatures to effect oil recovery, efficient heat transfer and... 

Mack, J.C., Smith, J.E., 1994. In-depth colloidal dispersion gels improve oil recovery efficiency. Paper SPE/DOE 27780 presented at the SPE/DOE Improved Oil Recovery Symposium, Tulsa, 17-20 April. 

Nelson, R.C., 1983. The effect of live crude on phase behavior and oil-recovery efficiency of surfactant flooding systems. SPEJ (June), 501—510. 

One of the main objectives of this study has been to determine the effect of interfacial properties on coalescence, emulsion stability and oil recovery efficiency for various surfactant and caustic systems. We have recently reported (6, 19) that for a petroleum sulfonate system there is no direct correlation between rates of coalescence and interfacial tension or interfacial charge. However, a qualitative correlation has been found between coalescence rates and interfacial viscosities. 

Further data on the effect of interfacial viscosity on emulsion stability and its subsequent effect on oil recovery efficiency by alkaline water flooding are needed. 

Previous work (1) in core floods with the system, Huntington Beach Crude vs. 0.5% Na SiO plus 0.75% NaCl, showed channeling of the crude oil during the injection of the caustic slug (Figure 6). The channeling phenomena along with the fact that emulsions were not observed until after 95% of the recovered oil was produced, could have lead to lower oil recovery efficiencies. To... 

Oil recoveries obtained from waterflooding (WF) and subsequent EOR phases of each coreflood are tabulated in Table IV. Also, the predicted ultimate waterflood oil recoveries which could be reached after infinite water throughput are included in Table IV. Moreover, Figure 4 displays the comparison of the oil recovery efficiencies of different processes applied in small radial cores. 

Healy and Reed (10) found (and others (11) have confirmed) that when the salinity of the brine is such that a Type III phase environment is formed in which the microemulsion (middle) phase contains equal volumes of brine and oil, the microemulsion/excess oil and microemulsion/excess brine interfacial tensions are nearly equal, the sum of those interfacial tensions is at or close to minimum and oil recovery efficiency is at or close to maximum. 

Oil recovery efficiency for each chemical flood, expressed as percent pore volume of oil produced by the flood, is indicated by the number of the left of each arrow. That is, the percent pore volumes of oil produced by the chemical floods were 29, 28, 24, and 12 for the floods with drives containing 5, 16, 32 and 45 percent SDSW respectively. The average waterflood residual oil saturation, before the chemical flood, in these experiments was 31.9 percent pore volume. 

Although sodium orthosilicate and sodium hydroxide exhibit similar behavior in reducing the hardness ion levels in the brine eluted from cores which do not contain oil, there is a significant increase in oil recovery efficiency when sodium orthosilicate solution is used as the preflush for a micellar-polymer recovery system. These results have been documented by Holm and Robertson (19) and some of the comparative data are shown in Table 6. 

Figure 1 is the cumulative oil recovery profile of the systems studied. It shows that with the addition of 0.06% IBA into the TRS 10-410/n-dodecane system, the oil recovery by direct surfactant solution flooding (i.e., without waterflooding) is improved from 84.37% to 98.32% after 3.5 PV surfactant solution injection. The TRS 10-80/n-octane system showed an increase in oil recovery from 60% to 91% by the addition of isobutanol (Figure 1). It should be noted that the increase in oil recovery occurs only after the major oil bank comes out (i.e., after 1 PV of produced fluid). We propose that the presence of isobutanol promotes the coalescence of oil droplets in porous media leading to a better oil recovery efficiency. A much more drastic difference is seen in the TRS 10-80/n-octane system, where the tertiary oil recovery increased from 0% without IBA to 76.84% with IBA (Table 1) after 2.7 PV surfactant solution injection. Thus, for both secondary and tertiary oil recovery processes (i.e., with or without brine flooding stage) carried out in these laboratory scale experiments, the addition of isobutanol enhances the oil recovery efficiency presumably by promoting the coalescence in porous media.

When the partition coefficient is near unity, a maximum surface concentration of the surfactant is achieved. In flow through porous media, it is expected that achieving the equilibrium condition may take much longer time. Therefore, we investigated the equilibrated and nonequilibrated systems in porous media to elucidate their effect on the oil recovery efficiency. 

For equilibrated systems, there is an excellent correlation between the capillary number and oil recovery efficiency. However, in calculating capillary number for nonequilibrated systems, care should be exercised because the IFT measured in vitro may not be achieved in situ and, in certain cases, the interfacial viscosity and not interfacial tension, may be a predominant factor influencing the oil displacement efficiency. 

These results suggest that, for the present system, polymer solution salinity is far more critical than connate water salinity in tertiary oil recovery. In other words, the processes occurring at surfactant slug-polymer solution interface determines the final oil saturation and oil recovery efficiency in the systems reported here. Gupta and Trushenski (6) also suggested that oil recovery is controlled by the composition developing in the micellar-polymer... 

In summary, as shown in Figure 9, the salinity shock design of mobility pol)niier solution can provide ultra low interfacial tension at microemulsion/polymer solution interface, reduce surfactant loss, and achieve high oil recovery efficiency. The poly-... 

When the salinity of pol)nner solution was at the optimal salinity of the preceding surfactant formulation, oil recovery in sand packs was favorable over a wide range of connate water salinities for both aqueous and oleic surfactant formulations. Oil recovery drastically decreased when the salinity of polymer solution was shifted from the optimal salinity even when the connate water was at the optimal salinity. These results indicate that the processes occurring at the surfactant slug-polymer solution mixing zone dominate the oil recovery efficiency. 

Lewis, A. Singsaas, I. Johannessen, B.O. Jensen, H. Lorenzo, T. Nordvik, A.B. Large Scale Testing of the Effect of Demulsifier Addition to Improve Oil Recovery Efficiency, MSRC Technical Report Series Report 95-033, Marine Spill Response Corporation, Washington, DC, 1995. 

Knowledge of the mechanisms of the entrapment of non-wetting fluids within porous media is important in a number of fields of study. The mercury extrusion curve in porosimetry potentially contains useful information on the nature of a porous structure. However, in order to extract that information it is necessary to have an understanding of how the entrapment of mercury arises. Mercury porosimetry is also often used in the oil industry to evaluate reservoir rook cores. This is because the mercury recovery efficiency is expected to provide an indication of the oil recovery efficiency in a strongly water-wet system. 

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