Oil entrapment

Micellar-polymer flooding and alkali-surfactant-polymer (ASP) flooding are discussed in terms of emulsion behavior and interfacial properties. Oil entrapment mechanisms are reviewed, followed by the role of capillary number in oil mobilization. Principles of micellar-polymer flooding such as phase behavior, solubilization parameter, salinity requirement diagrams, and process design are used to introduce the ASP process. The improvements in ""classicaV alkaline flooding that have resulted in the ASP process are discussed. The ASP process is then further examined by discussion of surfactant mixing rules, phase behavior, and dynamic interfacial tension. 

Oil Entrapment Mechanisms. Enhanced oil recovery processes depend in large part on the elimination or reduction of capillary forces. Capillary forces are the strongest that occur under typical reservoir conditions, and are most responsible for oil entrapment. Viscous forces, which act to displace oil, are composed of the applied pressure gradient, gravity, density differences between phases, and viscosity ratio. In a permeable medium, capillary forces result when the pores constrain the oil-water interface to a high degree of curvature. From the Laplace equation, the capillary pressure in a capillary tube can be derived ... 

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. 

Capillary Forces The interfacial forces acting among oil, water, and solid in a porous medium. These determine the pressure difference (capillary pressure) across an oil-water interface in a pore. Capillary forces are largely responsible for oil entrapment under typical reservoir conditions. 

The extensive research on microemulsions was prompted by two oil crises in 1973 and 1979, respectively. To optimise oil recovery, the oil reservoirs were flooded with a water-surfactant mixture. Oil entrapped in the rock pores can thus be removed easily as a microemulsion with an ultra-low interfacial tension is formed in the pores (see Section 10.2 in Chapter 10). Obviously, this method of tertiary oil recovery requires some understanding of the phase behaviour and interfacial tensions of mixtures of water/salt, crude oil and surfactant [4]. These in-depth studies were carried out in the 1970s and 1980s, yielding very precise insights into the phase behaviour of microemulsions stabilised by non-ionic [5, 6] and ionic surfactants [7-9] and mixtures thereof [10]. The influence of additives, like hydro- and lyotropic salts [11], short- and medium-chain alcohols (co-surfactant) [12] on both non-ionic [13] and ionic microemulsions [14] was also studied in detail. The most striking and relevant property of micro emulsions in technical applications is the low or even ultra-low interfacial tension between the water excess phase and the oil excess phase in the presence of a microemulsion phase. The dependence of the interfacial tension on salt [15], the alcohol concentration [16] and temperature [17] as well as its interrelation with the phase behaviour [18, 19] can be regarded as well understood. 

Mishra, S.K. Pathak, K. Formulation and evaluation of oil entrapped astroretentive floating gel beads of loratadine. Acta Pharm. 2008, 58 (2), 187-197. 

Detoni, C. B., Oliveira, D. M., Santos, I. E., Sao Pedro, A., El-Bacha, R., Velozo, E. S., Ferreira, D., Sarmento, B., and Cabral-Albuquerque, E. C. M. (2012). Evaluation of thermal oxidative stability and antiglioma activity of Zanthoxylum tingoassuiba essential oil entrapped into multi- and unilamellar liposomes. Journal of Liposome Research, 22, 1-7. 

Fabrication Various multiple-unit floating systems have been developed in different forms and are based on various principles, such as air compartment multiple-unit system, microparticles based on porous carriers, hollow microspheres (microballoons), and oil-entrapped gel beads prepared by gelation method... 

Comparative gas-chromatographic studies, following the heat treatment proved, that the thermal stability of the volatiles /e.g eucalyptus oil/ entrapped into P-cyclodext-rin greatly surpassed that of the traditionally applied ones /See Fig l./... 

Solvent Evaporation. This encapsulation technology involves removing a volatile solvent from either an oil-in-water, oil-in-oil, or water-in-oH-in-water emulsion (19,20). In most cases, the shell material is dissolved in a volatile solvent such as methylene chloride or ethyl acetate. The active agent to be encapsulated is either dissolved, dispersed, or emulsified into this solution. Water-soluble core materials like hormonal polypeptides are dissolved in water that contains a thickening agent before dispersion in the volatile solvent phase that contains the shell material. This dispersed aqueous phase is gelled thermally to entrap the polypeptide in the dispersed aqueous phase before solvent evaporation occurs (21). 

Thermal shock failures using water result from the water vapor entering the enamel layer through small, submicroscopic cracks formed at the instant of shock. The water condenses in the cracks and in the bubbles of the enamel traversed by the cracks. On subsequent heating, the vapor from the entrapped water expands to cause spalling of the enamel layer. Other quenchant Hquids, such as toluene, oils, and other organic Hquids, also cause fine, almost invisible cracks, but thermal shock failures do not result with these quenchants on subsequent heating (39). 

Natural Gas Natural gas is a combustible gas that occurs in porous rock of the earth s crust and is found with or near accumulations of crude oil. It may occur alone in separate reservoirs, but more commonly it forms a gas cap entrapped between petroleum and an impervious, capping rock layer in a petroleum reservoir. Under high-pressure conditions, it is mixed with or dissolved in crude oil. Natural gas termed dry has less than 0.013 dmVm (0.1 gaLlOOO fF) of gasoline. Above this amount, it is termed wet. 

Tar sands (oil sands) are large deposits of sand saturated with bitumen and water. Tar sand deposits are commonly found at or near the earth s surface entrapped in large sedimentary basins. Large accumulations of tar sand deposits are few. About 98% of all world tar sand is found in... 

Vinyls Vinyl chloride co-polymer resins were developed in the USA in the late 1930s. They have better weather and slightly more chemical resistance than chlorinated rubber paints. They are generally resistant to crude oil but application is more critical. For example, they are particularly sensitive to moisture present on a surface during painting and this can lead to adhesion failure. They are also more prone to solvent entrapment than chlorinated rubber paints. 

Phase separation microencapsulation procedures are suitable for entrapping water-soluble agents in lactide/glycolide excipients. Generally, the phase separation process involves coacervation of the polymer from an organic solvent by addition of a nonsolvent such as silicone oil. This process has proven useful for microencapsulation of water-soluble peptides and macromolecules (48). 

Lipase from C. rugosa entrapped on polyethylene glycol Iso-octane-water (4/1) Olive oil hydrolysis 35 41.5 /xmol/(min g of support) 0.043% w/v 121... 

---