Foam propagation

Sydansk, R.D., Polymer-Enhanced Foam Propagation Through High-Permeability Sandpacks Proceedings, Intemat. Symp. Oilfield Chem., Society of Petroleum Engineers Richardson, TX, 1993, SPE paper 25175. 

Retention in Porous Media. Anionic surfactants can be lost in porous media in a number of ways adsorption at the solid—liquid interface, adsorption at the gas—liquid interface, precipitation or phase-separation due to incompatibility of the surfactant and the reservoir brine (especially divalent ions), partitioning or solubilization of the surfactant into the oil phase, and emulsification of the aqueous phase (containing surfactant) into the oil. The adsorption of surfactant on reservoir rock has a major effect on foam propagation and is described in detail in Chapter 7 by Mannhardt and Novosad. Fortunately, adsorption in porous media tends to be, in general, less important at elevated temperatures 10, 11). The presence of ionic materials, however, lowers the solubility of the surfactant in the aqueous phase and tends to increase adsorption. The ability of cosurfactants to reduce the adsorption on reservoir materials by lowering the critical micelle concentration (CMC), and thus the monomer concentration, has been demonstrated (72,13). 

Figure 10. The effect of prefoam slug injected prior to foam formation on the rate of foam propagation.

This chapter reports adsorption data for a number of surfactants suitable for mobility control foams in gas-flooding enhanced oil recovery. Surfactants suitable for foam-flooding in reservoirs containing high salinity and hardness brines are identified. The results of adsorption measurements performed with these surfactants are presented surfactant adsorption mechanisms are reviewed and the dependence of surfactant adsorption on temperature, brine salinity and hardness, surfactant type, rock type, wettability and the presence of an oil phase is discussed. The importance of surfactant adsorption to foam propagation in porous media is pointed out, and methods of minimizing surfactant adsorption are discussed. 

Surfactant Adsorption. Surfactant propagation is crucial to foam propagation. The data compiled in later sections of this chapter show that surfactants that are similarly effective as gas mobility reducing agents may have significant differences in adsorption levels. The level of surfactant adsorption and its dependence on parameters such as brine salinity and hardness may then be the deciding factors in surfactant selection for a specific application. 

One of the factors that determines foam propagation and foam-flood economics is surfactant loss in the reservoir, most importantly adsorption at the solid—liquid interface. Adsorption levels of foaming surfactants, mostly those suitable for high salinity conditions, cover a wide range and lead to vastly different distances of foam propagation. Therefore, selection of a surfactant with minimal adsorption levels for the reservoir conditions of interest is crucial. 

In addition to the mobihty control characteristics of surfactants, critical issues in gas mobihty control processes are surfactant salinity tolerance, hydrolytic stabihty under reservoir conditions, surfactant propagation through the reservoir, and foam stabihty in the presence of cmde oil saturations. 

High temperature steam cools and eventually condenses as it propagates through the oil reservoir. To maintain foam strength as the steam cools, a noncondensible gas, usually nitrogen or methane, is often added to the injectant composition (196). Methods of calculating the optimum amount of noncondensible gas to use are available (197). 

Addition of up to 200 ppm sulfur dioxide to grape musts is customary. Strains of S. cerevisiae and S. bayanus grown in the presence of sulfite, become tolerant of fairly high concentrations of SO2. Cultures propagated in the winery are added in Hquid suspension, usually at 1—2% of the must volume. Many strains are available in pure culture. Factors such as flocculence, lack of foaming, fast fermentation, lack of H2S and SO2 formation, resistance to sulfur dioxide and other inhibitors, and flavor production will affect strain choice. No strain possesses all the desired properties. 

There are several ways to measure a material s resistance to tearing. In these tests, the applied force is not distributed over the entire specimen but is concentrated on a slit or notch and the tear strengtii is reported as the force required to propagate a tear from this point. For urethane elastomers and foams, the most... 

Earlier Kern River pilot results [59,82,83] showed that a steam foam formulation based on AOS containing 16-18 carbon atoms in the hydrophobe improves sweep efficiency and oil recovery of the steam drive but propagates relatively slowly and leaves the same residual oil saturation (ROS) as steam. 

Polymerization of the oxiranes is typically propagated from a starter molecule that is chosen to define the functionality if) of the final polyol. The functionality and the molecular weight of polyols are the main design features that define the polyurethane properties in the end-use applications. Additionally, the balance of EO and PO in the polyether polyols, mainly for flexible foam polyols, is tailored to enhance the compatibility of formulations and the processability of the foam products. The exact composition of the polyols defines the crucial performance features of the final polyurethane product. Even seemingly small differences in polyol composition can result in changes to polyol processabihty and polyurethane performance. This becomes a crucial issue when replacing conventional petrochemical polyols with polyols from different feedstocks. To demonstrate the sensitivity of commercial formulations to changes in feedstocks, a simple example is offered below. 

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