Viscous acid systems

Acid fracturing is a treatment in which the fracturing and etching fluids are acid. The fracture is created with a viscous acid system, for example, which also etches the walls of the fracture dining the injection process. These days, either term, fracture acidizing or acid fracturing, may be used to describe the process of creating an acid-etched fracture in a carbonate formation. 

Viscous acid fracturing uses viscous acid systems such as gelled, emulsified, and foamed acid, or chemically retarded adds, to both create the fracture and differentially etch the fracture face. Treatments with viscous acid are applicable in heterogeneous carbonates such as dolomites or impure limestones. 

Extended shut-in is usually not a major concern in carbonate acidizing— at least not from the standpoint of unwanted reprecipitation reactions. However, it is best to prepare a well to be returned to production as soon as possible, if there is no reason to shut the well in or to allow for a soak period. Viscous acid systems, especially gels, should be produced back as soon as possible, especially at higher temperatures (>200°F). 

EPDM-ZnO-stearic acid systems could not be extruded even at 190°C. This is not unexpected since the material, in the absence of zinc stearate, shows no transition from the rubbery state to the viscous flow state (Fig. 1). In the presence of 10 phr of zinc stearate, the m-EPDM-ZnO-stearic acid system could be extruded but melt fracture occurred at a lower temperature (150°C) at all shear rates. At 160°C and 170°C, however, the extrudates showed melt fracture only at high shear conditions. At 20 phr loading of zinc stearate, melt fracture of the extrudate occurred at high shear conditions at 150°C, but at higher temperatures no melt fracture occurred and the extrusion was smooth under all shear conditions. At 30 and 40 phr loadings of zinc stearate, the extrudates were smooth under all shear conditions at all temperatures. 

Another early attempt to formulate a nanoparticulate system for the delivery of pilocarpine was made by Gurny [99], This formulation was based on pilocarpine dispersed in a hydrogen CAP pseudolatex formulation. Gurny and co-workers [101] compared the formed nanoparticles to a 0.125% solution of hyaluronic acid some years after their first investigation and found that the viscous hyaluronic acid system showed a significantly longer retention time in front of the eye than the pseudolatex formulation. 

The change in the viscous properties of solutions and consequently the torque (power consumed) on the mixer shaft is directly correlated with the phase transitions in the PPTA-sulfuric acid system (Fig. 10.3) [24]. In passing through a critical concentration, i.e, from iso- to anisotrqiic solutions, an extreme dependence of the viscosity on the concentration with a maximum for phase inversion where the LC phase becomes a continuous matrix is obs ed. There is a sharp decrease in the viscosity, whose basic cause is the anisotropy of the viscosity (cf. ChaptCT 9), with a further increase in the concentration of the polymer. 

Currently, the commercial systems available that will result in the deepest penetration of acid are emulsified acid and, perhaps, surfactant-gelled acid. Viscous acids may contain a fluid-loss additive, such as an oil-soluble resin or polymer, to reduce leak-off. Particulate diverters are not effective in fracture acidizing, but in matrix treatments, they can make a difference. 

The sodium salt of CS [9005-22-5] is prepared by reaction of cellulose with sulfuric acid in alcohol followed by sodium hydroxide neutrali2ation (20). This water-soluble product yields relatively stable, clear, and highly viscous solutions. Introduced as a thickener for aqueous systems and an emulsion stabilizer, it is now of no economic significance. 

Polybutenes. Copolymerization of mixed isobutylene and 1-butene containing streams with a Lewis acid catalyst system yields low mol wt (several hundred to a few thousand) copolymers that are clear, colorless, viscous Hquids. The chain-ends are unsaturated, and they are often chemically modified through this functionaUty (7,73). 

In a gas and liquid system, when gas is introduced into a culture medium, bubbles are formed. The bubbles rise rapidly through the medium and dispersion of the bubbles occurs at surface, forming froth. The froth collapses by coalescence, but in most cases the fermentation broth is viscous so this coalescence may be reduced to form stable froth. Any compounds in the broth, such as proteins, that reduce the surface tension may influence foam formation. The stability of preventing bubbles coalescing depends on the film elasticity, which is increased by the presence of peptides, proteins and soaps. On the other hand, the presence of alcohols and fatty acids will make the foam unstable. 

The above difference in reactivity of benzene and toluene is close to that observed in a less viscous system so that the results for compounds of the reactivity of benzene (and perhaps toluene) or less in these media are meaningful, but not for compounds which are normally more reactive. This conclusion was confirmed for nitration in nitric acid-perchloric acid of a range of compounds which normally are fairly reactive. The derived second-order rate coefficients (10k2) for nitration... 

Polycondensation At room temperature, 0.4% mass of Sn(II) chloride dihydrate (SnCl2-2H20) and 0.4% mass of p-toluenesulfonic acid monohydrate (p-TSA) are introduced into the mixture. The mixture is heated to 180°C under mechanical stirring. The pressure is reduced stepwise to reach 13 mbar, and file reaction is continued for 20 h. The reaction system becomes gradually viscous, and a small amount of L-lactide is formed and refluxed through the reflux condenser. At file end of the reaction, the flask is cooled down, file product is dissolved in chloroform and subsequently precipitated into diethyl ether. The resulting white fibrous solids are filtered and dried under vacuum (average yield 67%). 

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]. 

Abstract. Auto-accelerated polymerization is known to occur in viscous reaction media ("gel-effect") and also when the polymer precipitates as it forms. It is generally assumed that the cause of auto-acceleration is the arising of non-steady-state kinetics created by a diffusion controlled termination step. Recent work has shown that the polymerization of acrylic acid in bulk and in solution proceeds under steady or auto-accelered conditions irrespective of the precipitation of the polymer. On the other hand, a close correlation is established between auto-acceleration and the type of H-bonded molecular association involving acrylic acid in the system. On the basis of numerous data it is concluded that auto-acceleration is determined by the formation of an oriented monomer-polymer association complex which favors an ultra-fast propagation process. Similar conclusions are derived for the polymerization of methacrylic acid and acrylonitrile based on studies of polymerization kinetics in bulk and in solution and on evidence of molecular associations. In the case of acrylonitrile a dipole-dipole complex involving the nitrile groups is assumed to be responsible for the observed auto-acceleration. 

---