Gelation behavior as a function of concentration of sodium thiosulfate for PAM gels cross-linked with chromium

Abstract

Existing reducing agents for cross-linking polymers are expensive and toxic and mostly limited for water shut off applications. A gelation study was performed on a safer, cheaper, more soluble, and short-lived gel by cross-linking polyacrylamide and chromium as a cross-linking agent using a rheometer and bead-pack porous media. The effect of concentration of sodium thiosulfate as the reducing agent was investigated to determine conditions for optimum yield strength and the gelation time and behavior which has never been published before. For a fixed minimum concentration (for the gel to form) of polyacrylamide and sodium dichromate, the gel yield strength vs. sodium thiosulfate concentration showed a somewhat bell-shaped curve initially increasing, reaching a peak at 2000 ppm, and then starting to decrease. The gelation formed by sodium thiosulfate was comparatively weak and short lived as compared to the ones formed by other reducing agents. Gel started to form instantaneously, reached a peak in 2 h, began to decrease, and then stabilized at 40 cp. The mobility reduction trends were similar to the yield strength curve. The short-lived gel could be useful to improve the waterflood mobility ratio far away from the wellbore without compromising on ease of injectivity.

Chemical and Physical Architecture of Macromolecular Gels for Fracturing Fluid Applications in the Oil and Gas Industry; Current Status, Challenges, and Prospects

“…Fracturing fluids to form gels typically requires a polymer concentration of 20-40 pptg [159]. A polyacrylamide polymer with carboxyl groups is crosslinked, resulting in a gel, as shown below in Figure 13 [160]. PAM and HPAM samples exhibit non-Newtonian behavior, with shear-thinning below the critical shear rate and shear-thickening above it.…”

Perspective Review of Polymers as Additives in Water-Based Fracturing Fluids

“…13 Figure 4 illustrates a cross-linking method of a polyacrylamide polymer containing carboxyl groups, by which polymer chains are connected, forming a cross-linked gelled polymer. 19 2.2. Application of Polymers in Fracturing Fluids.…”

“…The typical polymer concentration used in fracturing fluids to cross-link and create gels is 20–40 pptg Figure illustrates a cross-linking method of a polyacrylamide polymer containing carboxyl groups, by which polymer chains are connected, forming a cross-linked gelled polymer …”

An experimental study comparing the stability of colloidal dispersion gels with normal polymeric solutions for enhanced‐oil‐recovery purposes

“…[ 10 ] Anionic polyacrylamide (HPAM and SPAM) and chromium (III) acetate are used to prepare polymer gels. [ 23,24 ] In bulk gels, gels formed in high concentrations of polymer and crosslinker, polymer molecules form inter‐molecular crosslinks, meaning that a polymer molecule is linked to other polymer molecules via multivalent cations. Forming a continuous series of links, a 3D structure is formed, which is neither liquid nor solid, known as bulk gel, with a final viscosity much higher than the pure polymer solution before adding the crosslinker (this property is used as the simplest means of ascertaining bulk gel formation).…”