Slow‐gelling Cr⁺³/polyacrylamide solutions for reservoir profile modification: Dependence of the gelation time on pH

Abstract

SYNOPSISSystematic studies of the gelation of both buffered and unbuffered aqueous Crf3/polyacrylamide solutions show that the gelation time is a strong function of pH, increasing by about one order of magnitude per unit decrease in pH for polyacrylamides less than about 7.5% hydrolyzed. The gelation rate also depends strongly on the Cr+3 concentration, the degree of polymer hydrolysis, and temperature. At 25"C, gelation delays of more than 10 months have been obtained; the maximum delay observed at 60°C is about 1 month and at 90°C 1 d. The resistance of buffered gel solutions to change in p H results in significantly longer gelation times at 90°C and low pH than for identical unbuffered solutions; at lower temperatures, however, the differences are insignificant. Most importantly, the use of low pH to control the gelation time of Cr+3/polymer solutions provides an attractive, inexpensive substitute for the environmentally unacceptable Cr+6/ reductant method currently employed for profile modification treatments.

A novel thermoviscosifying water‐soluble polymer: Synthesis and aqueous solution properties

“…Polyacrylamide (PAM), as obtained by free radical homopolymerization of acrylamide, is one of the most widely used and technically important watersoluble polymeric materials. 1 Applications of PAM can be found in various areas, ranging from gel electrophoresis 2 and chromatography column, 3 soil amendment and conditioning, 4,5 coal and mineral processing, 6,7 papermaking, 8 water purification, 9 drag reduction, 10 to oil production processes including oilwell drilling, 11 reservoir stimulation, 12 water shutoff, 13 profile modification, 14 and particularly tertiary oil recovery. 15,16 When used in petroleum industry, nevertheless, one of the main problems PAM encountered is its poor thermal stability at elevated temperature that is normally found in oil reservoir conditions.…”

Fabrication and Characterization of Polysaccharide Metallohydrogel Obtained from Succinoglycan and Trivalent Chromium

“…This is related to the nature of interactions based on the structure of the chromium species formed in water and formation of carboxyl groups. In extremely acidic conditions (such as a pH less than 3), Cr 3+ predominantly exists in the monomeric form, and (Cr(H 2 O) 6 ) 3+ is co-ordinated with six water molecules [ 61 , 62 ]. Given that the Cr 3+ monomer is small, it cannot be effectively co-ordinated with the carboxyl group (pK a ~3.8) of succinoglycan, where protonation of the carboxylic group can also impede their interactions with Cr 3+ [ 63 ].…”

pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions

“…An explanation was related to the fact that, at different pH, various chromium species are formed, which cross-link xanthan more or less efficiently. In particular, authors assumed that, in the studied pH range of 2.5-5, Cr(OH)(H 2 O) 5 2+ and Cr(OH) 2 (H 2 O) 4 2+ hydroxides are formed with increasing pH, and they react faster with polymer carboxylic groups than Cr(H 2 O) 6 3+ ion, which is initially formed after dissolution of Cr(III) salts in water [30]. In the work [22] it was discovered that the elastic modulus of xanthan gels reaches a maximum at a certain pH values, which are different for Fe 3+ , Al 3+ and Cr 3+ .…”