Emulsion Flooding

Optimizing the formulation of micellar surfactant solutions used for enhanced oil recovery consists of obtaining interfacial tensions as low as possible in multiphase systems, which can be achieved by mixing the injected solution with formation fluids. The solubilization of hydrocarbons by the micellar phases of such systems is linked directly to the interfacial efficiency of surfactants. Numerous research projects have shown that the amount of hydrocarbons solubilized by the surfactant is generally as great as the interfacial tension between the micellar phase and the hydrocarbons. The solubilization of crude oils depends strongly on their chemical composition [155]. 

Micellar flooding is a promising tertiary oil-recovery method, perhaps the only method that has been shown to be successful in the field for depleted light oil reservoirs. As a tertiary recovery method, the micellar flooding process has desirable features of several chemical methods (e.g., miscible-type displacement) and is less susceptible to some of the drawbacks of chemical methods, such as adsorption. It has been shown that a suitable preflush can considerably curtail the surfactant loss to the rock matrix. In addition, the use of multiple micellar solutions, selected on the basis of phase behavior, can increase oil recovery with respect to the amount of surfactant, in comparison with a single solution. Laboratory tests showed that oil recovery-to-slug volume ratios as high as 15 can be achieved [439]. 

A solids-stabilized water-in-oil emulsion may be used either as a drive fluid for displacing hydrocarbons from the formation or to produce a barrier for diverting the flow of fluids in the formation. The solid particles may be formation solid particles or nonformation solid particles, obtained from outside the formation (e.g., clays, quartz, feldspar, gypsum, coal dust, asphaltenes, polymers) [228,229]. 

The problems of enhanced oil-recovery methods have been summarized by Bragg [230]  

Oil recovery is usually inefficient in subterranean formations (hereafter 

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Microemulsion, or micellar/emulsion, flooding an augmented waterflooding technique in which a surfactant system is injected in order to enhance oil displacement toward producing wells. 

It is concluded that carbon dioxide foam or emulsion flooding has great promise. The oil recovery is significantly higher than with the use of WAG at the same water - carbon dioxide ratio. 

Fiori and Farouq Ali (73) proposed the emulsion flooding of heavy-oil reservoirs as a secondary recovery technique. This process is of interest for Saskatchewan heavy-oil reservoirs, where primary recovery is typically 2-8%. Water-flooding in these fields produces only an additional 2-5% of the original oil in place because of the highly viscous nature of the oil. In laboratory experiments, a water-in-oil emulsion of the produced oil is created by using a sodium hydroxide solution. The viscous emulsion formed is injected into the reservoir. Its high viscosity provides a more favorable mobility ratio and results in improved sweep of the reservoir. Important parameters include emulsion stability and control of emulsion viscosity. 

Reed, R.L., Carpenter Jr., C.W., 1982. Shear-stabilized emulsion flooding process. US patent No. 4,337,159, 29 June. 

The emulsion behaviour in porous media is discussed in [235]. O/w emulsions with volume fractions of up to 50% show Newtonian behaviour, whereas those with more than 50% are non-Newtonian liquids, the apparent viscosity of which depends on the shear rate. The viscosities of such emulsions are more than 20 times that of water and sometimes can be even comparable with that of oil. When the emulsion is moving, a temporary permeability reduction of the reservoir may occur due to the capture of small droplets by the surface of the porous medium. In this case, stable o/w emulsions may flow not as a continuous liquid, i.e. the emulsion flow largely depends on the nature of the porous medium. Therefore, it is necessary to know about the structure and physicochemical characteristics of the oil reservoir (porous medium) porosity, the mean pore diameter, the mean pore size and pore size distribution, chemical composition of the minerals ( acidic , basic , neutral ), the nature of the pore surface, first of all wettability, for a successful application of the emulsion flooding method. 

McAuliffe, C. D., "Oil-in-Water Emulsions and Their Flow Properties in Porous Media", JPT. June 1973, pp. 727-733. D"Elia-So, R. Ferrer-G, J., "Emulsion Flooding of Viscous Oil Reservoirs", SPE 4674. 48th Annual Fall Meeting. Las Vegas, Nevada, September 30 - October 3, 1973. 

Results described in the literature have resulted in several patents, such as one for the improvement of the transport of viscous crude oil by microemulsions based on ether carboxylates [195], or combination with ether sulfate and nonionics [196], or several anionics, amphoterics, and nonionics [197] increased oil recovery with ether carboxylates and ethersulfonates [198] increased inversion temperature of the emulsion above the reservoir temperature by ether carboxylates [199], or systems based on ether carboxylate and sulfonate [200] or polyglucosylsorbitol fatty acid ester [201] and eventually cosolvents which are not susceptible for temperature changes. Ether carboxylates also show an improvement when used in a C02 drive process [202] or at recovery by steam flooding [203]. 

Polyalkylene polyamine salts are prepared by contacting polyamines with organic or inorganic acids. The polyamines have a molecular weight of at least 1000 Dalton and ranging up to the limits of water solubility [1185]. In a process of demulsification of the aqueous phase of the broken bitumen emulsions, the pH is adjusted to deactivate the demulsifier so that the water may be used in subsequent in situ hot water or steam floods of the tar sand formation. 

In the water-flooding process, mixed emulsifiers are used. Soluble oils are used in various oil-well-treating processes, such as the treatment of water injection wells to improve water injectivity and to remove water blockage in producing wells. The same method is useful in different cleaning processes with oil wells. This is known to be effective since water-in-oil microemulsions are found in these mixtures, and with high viscosity. The micellar solution is composed essentially of hydrocarbon, aqueous phase, and surfactant sufficient to impart micellar solution characteristics to the emulsion. The hydrocarbon is crude oil or gasoline. Surfactants are alkyl aryl... 

In the emulsion regime, there is little entrainment of liquid by the vapour. Instead, the high liquid load causes the downcomer to overfill and the tray to flood. 

In the froth regime, which is between the spray and emulsion ones, flooding may be by either mechanism, depending on the tray spacing and the particular combination of vapour and liquid loads. 

The tray may flood. Water and hydrocarbon mixing on the tray deck, stirred up by the flowing gas, creates an emulsion. The emulsion does not separate as readily as clear liquid from the gas. Premature downcomer backup, followed by tray deck flooding, result. 

Effect of column diameter (at constant UV and percent of flood). As column diameter increases, both the liquid and vapor flow rates increase as the square of the diameter. The area for vapor flow also increases as the square of the diameter, so the vapor load remains unaffected. On the other hand, the area available for liquid flow only increases in proportion to the diameter. Therefore, the liquid rate per unit of weir length increases, the increase being proportional to the column diameter. The operating point on Fig. 6.29 will therefore shift horizontally to the right, toward the emulsion regime. Increasing the number of liquid passes on the tray reverses the above action, and shifts the operating point back to the left. 

Section 6.2.11 recommends the use of Fair s entrainment correlation in the froth (and emulsion) regime. This section also states that entrainment in the emulsion regime is unlikely to be a problem. Fair s correlation (Fig. 6.16) predicts fractional entrainment (pound of entrained liquid per pound of liquid) of 0.0 ll and 0.0075 at 80 percent of flood for the top and bottom trays, respectively. Even at 90 percent of... 

Summary. The third trial checks well against the various hydraulic criteria. Column capacity is limited by downcomer backup flood in the bottom section center-to-side trays (i.e., side downcomers). All trays will operate in the emulsion regime. 

Many uses of dextran in petroleum production have been proposed. It has been tested successfully for use in drilling muds,354,355 and in viscous water-flooding.356,357 The patent literature332 suggests that the native, high-molecular-weight dextran is now used in various proprietary, X-ray and photographic emulsions. 

In most applications of CO2 as an oil recovery agent, the CO2 exists as a supercritical fluid above its critical pressure (7.4 MPa) and temperature (32°C), while its solutions in oil are liquids (5). Hence, the dispersion types of most direct interest are supercritical-fluid-in-a-liquid (for which no specific name yet exists) and emulsions of oleic-in-aqueous liquids (which may be encountered at low CO2 saturations). However, for historical reasons (described below), all dispersions used in research on gas-flood mobility control are sometimes called "foams," even when they are known to be of another type. 

For mechanistic studies, ambient pressure experiments on emulsions and foams often offer significant experimental advantages over high-pressure experiments. However, high-pressure measurements are also needed since the phase behavior, physical properties of the fluids, and dispersion flow may all depend on pressure. Experiments under laboratory conditions that closely match reservoir conditions are particularly important in the design of projects for specific fields. Chapter 19, by Lee and Heller, describes steady-state flow experiments on CO2 systems at pressures typical of those used in miscible flooding. The following chapter, by Patton and Holbrook,... 

The cell tests consisted of three steps (1) In the first step, the cell was charged with approximately equal volumes of CO2 and an aqueous solution of the test surfactant in reservoir brine. The desired behavior was formation of an emulsion-like dispersion of the C02-rich phase in the aqueous phase. (2) In the second step, a small amount of reservoir oil was added. Desirable surfactants formed three-phase dispersions in which both the C02 rich and oil-rich phases were dispersed in the aqueous phase. (The crude oil was not miscible with CO2.) (3) In the third step of the test, the amount of oil in the cell was increased until it was somewhat larger than the volumes of CO2 and of aqueous phase. Although relatively few surfactants passed this third step, the desired dispersion structure was believed to be droplets of the C02-rich phase dispersed in the continuous oleic phase, with films of aqueous surfactant solution encasing the dispersed droplets (42,43, S. L. Wellington, Shell Development Company, personal communication, November 13, 1987). "Foaminess" tests performed under these conditions correlated with the results of flooding experiments. Both nonionic alkoxylated surfactants and their anionic sulfonated derivatives were tested by these methods (42,43). 

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