Polymer rock surface effect

The efficiency and economics of oil recovery can be adversely affected by interactions between surfactant aggregates and polymer. Such interactions occur because of mixing at the boundary between surfactant and buffer solutions, and because residual surfactant adsorbed on the rock surface may later desorb into polymer solution. Mixing of polymer and surfactant may also occur throughout the surfactant bank because of the "polymer inaccessible pore volume" effect (1 ). Large polymer molecules are excluded from the smaller pores in the reservoir rock, and travel faster than the surfactant. Thus, polymer molecules enter into the surfactant slug. 

On the basis of Figures 15-17, it may be stated that in an oil-wet system the flow of the polymer solution advancing connate water and distilled water takes place with its initial viscosity and mobility further, that in the porous media no apparent permeability reduction occurs. With knowledge of the close relationship between the polymer adsorbed on the rock surface and the flow characteristics, this phenomenon may be traced to the absence of an irreversible gel layer over the pore surface. On an oil-wet surface the quantity of polymer bound by chemisorption, regardless of the type, is zero, and thus the "sweep effect of the carrier phase is also perfect. 

A macromolecular picture of the effectiveness of polymeric surfactants in oil displacement from porous rock can be understood from the fact that polymers normally assume the coiled Gaussian chain configuration (Rodriguez et al., 2003). Under the shear field of a flow situation within the pores, the polymeric macromolecules assume an elongated configuration and would tend to lodge themselves onto the oil adjacent to the rock surfaces. 

Physically retarding acid reaction is accomphshed by thickening (viscosifying) the acid used. Viscous acids include polymer-gelled, surfactant-gelled, emulsified, and foamed acids. Combinations can also be used in addition, surfactant-retarded acid can be gelled or foamed. The intent of viscosifying acid is to slow the rate of acid diffusion outward, to the rock surfaces, and to reduce the rate of fluid loss from wormhole to unreacted matrix. Both of these effects work to increase live acid penetration distance. 

Physiochemical conditions at the solid surface-liquid interface are not identical to those in the bulk phase, i.e. the environment at the interface therefore will be different in terms of the concentrations of ions, small molecules or polymers. The chemical species concerned may be beneficial to the cells or toxic [Mozes and Rouxhet 1992]. Unlike natural surfaces such as rocks and stones the surfaces found in heat exchangers are usually metallic and may give rise to ions that are generally not present in natural aqueous systems. Vieira et al [1993] report that metallic ions such as and seem to interfere with the initial adhesion and development of biofilms formed from Pseudomonas fluorescens, whereas no such effect was observed with aluminium ions. 

In order to be able to Judge the injectability of a polymer solution in a pay zone, filterability tests with surface pre-fiIters alone are not sufficient. As well as the influence of shear rate within the pores of the formation the interaction between the rock matrix and polymer solution should also be considered due to the effect on processes such as adsorption and retention. 

Behavior of Gel Systems in Porous Media. The erosslinked polymer systems mixed at the surface are injected into a formation, where reaction occurs to form a gel. Ideally, once formed, the gel has sufficient strength or viscosity to be immobile. The effective permeability of the rock matrix or fractures in which the gel resides is reduced or, in some cases, essentially eliminated. For processes based on injection of slugs in which the different reactants reside, mixing followed by reaction occurs within the rock. The objective here also is to form a gel that is not mobile. 

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