Viscoelastic acid systems

Surfactant-gelled acid systems (also known as viscoelastic acid systems) represent a more recent development. Such systems have found success in carbonate matrix acidizing applications in particular. Certain special surfactant formulations can be added to acid that is above a certain concentration (e.g., >15% HCl) at which the surfactant does not impart appreciable viscosity. However, as the acid is injected and reacts in the formation, the surfactant generates viscosity (as a function of dissolved chloride ion and pH), thereby retarding reaction and providing, potentially, in situ diversion. As acid spends further, viscosity breaks back to reduced level (in the ideal case). 

Similar to Wu and Liao (75), Wu et al. (74) used a DMA (Model -242C, NETZSCH Co.) and a rheometer (HAAKE RS600, Thermo Electron Co.) to evaluate the viscoelastic behavior of the carboxylic-acid-functionalized MWCNTs reinforced PCL/PLA blend. Using DMA, it was observed that, with the increase of MWCNT loading, the Tg of the blend system shifted to higher temperatures. This agrees with the results obtained from the other studies discussed above and indicates the MWCNTs are compatible with the blend. The viscoelastic properties observed via rheometer were similar to those by Wu et al. (73), discussed above. 

Most biological systems are predominantly water, with other components conferring important structural and mechanical properties. The complexity of the fluid can have a substantial impact on rates of diffusional transport. For example. Chapter 5 discusses the consequences of having self-organized phospholipid phases (i.e., membrane bilayers) in systems that are primarily composed of water. Membranes separate the medium into smaller aqueous compartments, which remain distinct because the membrane permits the diffusion of only certain types of molecules between the compartments. Complex fluid phases have diverse roles in biological systems hyaluronic acid forms a viscoelastic gel within the eye (vitreous humor) that provides both mechanical structure and transparency actin monomers and polymers within the cytoplasm control cell shape and internal architecture. Drug molecules often must diffuse through these complex fluids in order to reach their site of action. 

Surface Viscosity of Protein Monolayers. Figure 2 shows the surface viscosity ( H g) of a number of proteins and one polyamino acid as a function of H ( ), The extremely high surface viscoelasticity of protein monolayers appears to be more characteristic of an interacting random chain system than an array of rigid helices. The theory of surface viscosity of Moore and Eyring ), based on the Theory of Absolute Reaction Rates, postulates that the flow of a monolayer consists of movements of flow units, normally molecules, from one equilibrium position to another, over an intermediate activation energy barrier. The equation derived for the coefficient of surface viscosity ( g)... 

When a desolubilizer is added to the acid formulation, an increase of the viscosity is observed, where the rod-like micelles increase in length. When the maximum viscosity is reached, a phenomenon occurs which is often observed with cationic surfactants, namely viscoelasticity. The latter occurs when the system of very long rod-like micelles with numerous entanglements becomes a stable, three-dimensional network, which at... 

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