Hydroxyethyl cellulose hydration

Controlling fluid loss loss is particularly important in the case of the expensive high density brine completion fluids. While copolymers and terpolymers of vinyl monomers such as sodium poly(2-acrylamido-2-methylpropanesulfonate-co-N,N-dimethylacrylamide-coacrylic acid) has been used (H)), hydroxyethyl cellulose is the most commonly used fluid loss additive (11). It is difficult to get most polymers to hydrate in these brines (which may contain less than 50% wt. water). The treatment of HEC particle surfaces with aldehydes such as glyoxal can delay hydration until the HEC particles are well dispersed (12). Slurries in low viscosity oils (13) and alcohols have been used to disperse HEC particles prior to their addition to high density brines. This and the use of hot brines has been found to aid HEC dissolution. Wetting agents such as sulfosuccinate diesters have been found to result in increased permeability in cores invaded by high density brines (14). 

The presence of anionic or cationic groups at a 0.4 M.S. level inhibited adsorption and interlayer entrapment of 2.0 M.S. hydroxyethyl cellulose(HEC) from fresh water solutions. The lack of adsorption of the cationic HEC is surprising it is related to hydration of the quaternary amine group. Increasing adsorption and interlayer entrapment is observed with both the cationic and anionic HECs with increasing sodium chloride concentration. 

The most widely used synthetic and natural enhanced oil recovery polymers, such as partially hydrolyzed polyacrylamide, carboxymethyl(ethyl) cellulose, polysaccharides, or xanthan gums, are not suitable for high-temperature reservoirs (> 90 °C) with high-density brine fluid due to excessive hydrolysis and precipitation [277]. The main advantages of polymeric betaines over the mentioned standard polymers are (1) thermostability (up to 120 °C) (2) brine compatibility and (3) viscosification in brine solution [278]. Carbobetaines grafted onto hydroxyethyl cellulose were tested as a drilling-mud additive for clay hydration inhibition and mud rheological control [279]. An increase in the content of carbobetaine moieties resulted in an enhanced inhibitive abiUty, especially for sahne mud. 

Ethylhydroxyethylcellulose is an ether of cellulose with both ethyl and hydroxyethyl substituents attached via ether linkages to the anhydroglucose rings. It swells in water to form a clear viscous colloidal solution. Preparation of solutions of cellulose derivatives requires hydration of the macromolecules, the rate of which is a function of both temperature and pH, as shown in the example in Fig. 8.f8. 

A systematic study has been reported concerning the influence of the specific water structure and diphylic nature of some cellulose ethers (methyl-, methyl-hydroxypropyl-, hydroxypropyl-, hydroxyethyl-, and hydroxyethylhydroxy-propyl-) on the properties of the aqueous solutions of these polysaccharide derivatives. The presence of non-polar groups in the cellulose ether macromolecule and of associated specific water structures account for the solution properties given by hydrophobic hydration and hydrophilic bonds. 

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