TX 75063-3636, U. S.A.,fax 01-972-952-9435. AbstractThis experimental investigation studied the use of additives to enhance foam properties and improve the in-situ generation of foams for improving gas flooding sweep efficiency. Some of the parameters affecting foam performance were polymer concentration, different surfactants and their concentration, aqueous phase salinity and pH, and effect of ffow rate (or shear rate).Performance of polymer enhanced foams (PEF) was much better when compared to conventional foams. Polyacrylamide polymers were used as an additive. Higher foam resistance and longer foam persistence were achieved by using relatively low concentrations of polymers. The studies also showed that the foam performance was significantly improved over a broad range of polymer concentrations.A number of other investigators have shown that foams are severely affected in the presence of oil. This is especially true of lighter or less viscous oils, and the destabilizing effect is magnified with a higher salinity aqueous phase. PEF with a low salinity aqueous phase showed improvement in foam stability. The effective viscosities of PEF were higher than those of conventional foams with a high salinity aqueous phase and the presence of lighter oils. Further, PEF reduced the negative impact of oils on foam mobility. Of the surfactants studied, alpha olefin sulfonates were tolerant to high salinity brines as well as being compatible with polymer additives. Other surfactants, including amine oxide surfactants, were also studied and showed unusually high foam resistance and stability. Introduction..__ ---_.. Because of recent advances in technology, C02 flooding has become a readily available improved oil recovery method. Significant amounts of residual oil can be recovered by carbon dioxide (COJ flooding. Studies' have shown increasing trends for C02 flood projects in the United States, as well as in other countries. However, many, if not all, gas flooding field projects are often hampered by early C02 breakthrough, poor sweep efficiency, and inefficient oil recovery due to viscous fingering resulted from a low gas phase visco-sity and an unfavorable mobility ratio.Poor sweep efficiency may also be caused by stratification or fracturing. Reservoir heterogeneity, particularly layering, is one of the most important factors that affects C02 flood performance. C02 mobility is usually high relative to that of other reservoir fluids, and the resulting unfavorable mobility ratio enhances fingering that initially results from reservoir heterogeneity or gravity override. In more heterogeneous reservoirs, the C02 floods some layers more easily because of differences in porosity and permeability. In this case, the C02 breaks through faster to the producing wells. More C02 is then required over the lifetime of the ffood, which leads to higher C02 costs per barrel of oil recovered and greater handling and recycle expenses.A need to control gas phase mobility has resulted in many studies of processes which may alleviate the adve...

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Experimental cloud point and bubble point data of ternary mixtures for poly­(vinylacetate) (PVAc) and cosolvents in carbon dioxide (CO2) are studied using the supercritical CO2 phase behavior device. The cloud point and bubble point pressures are determined by measuring the resistance variation of photoresistance. Acetate acid and ethyl acetate have been selected as the cosolvents. These systems show phase behavior over a temperature range of 308.2–338.2 K and pressure of up to 50 MPa. The transition point pressure increases as the temperature increases. The transition point isopleths for the PVAc + CO2 + cosolvent ternary systems show upper critical solution pressure types. The cloud point and bubble point curves for the PVAc + CO2 + cosolvent systems decrease rapidly as the cosolvent concentration increases. When the mass ratio of PVAc and cosolvents is fixed at 1:7, the transition point pressures increase as CO2 increases. Compared with acetic acid and ethyl acetate, the transition point pressures of the PVAc + CO2 mixtures, containing the two cosolvents, show that the pressure for acetate acid is less than that of ethyl acetate under the same conditions. The phase behaviors of these ternary systems are calculated using the perturbed-chain statistical associating fluid theory equation of state by adjusting the binary interaction parameter k ij. Our models are in very good agreement with the experimental data.

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