Effect of Magnesium and Iron on the Hydration and Hydrolysis of Guar Gum

Rheological Performance of High-Temperature-Resistant, Salt-Resistant Fracturing Fluid Gel Based on Organic-Zirconium-Crosslinked HPAM

Development of low-cost, high-temperature-resistant and salt-resistant fracturing fluids is a hot and difficult issue in reservoir fluids modification. In this study, an organic zirconium crosslinker that was synthesized and crosslinked with partially hydrolyzed polyacrylamide (HPAM) was employed as a cost-effective polymer thickener to synthesize a high-temperature-resistant and salt-resistant fracturing fluid. The rheological properties of HPAM in tap water solutions and 2 × 10⁴ mg/L salt solutions were analyzed. The results demonstrated that addition of salt reduced viscosity and viscoelasticity of HPAM solutions. Molecular dynamics (MD) simulation results indicated that, due to electrostatic interaction, the carboxylate ions of HPAM formed an ionic bridge with metal cations, curling the conformation, decreasing the radius of rotation and thus decreasing viscosity. However, optimizing fracturing fluids formulation can mitigate the detrimental effects of salt on HPAM. The rheological characteristics of the HPAM fracturing fluid crosslinking process were analyzed and a crosslinking rheological kinetic equation was established under small-amplitude oscillatory shear (SAOS) test. The results of a large-amplitude oscillation shear (LAOS) test indicate that the heating effect on crosslinking is stronger than the shear effect on crosslinking. High-temperature-resistant and shear-resistant experiments demonstrated good performance of fracturing fluids of tap water and salt solution at 200 °C and 180 °C.

Complex Fluids and Hydraulic Fracturing

Nearly 70 years old, hydraulic fracturing is a core technique for stimulating hydrocarbon production in a majority of oil and gas reservoirs. Complex fluids are implemented in nearly every step of the fracturing process, most significantly to generate and sustain fractures and transport and distribute proppant particles during and following fluid injection. An extremely wide range of complex fluids are used: naturally occurring polysaccharide and synthetic polymer solutions, aqueous physical and chemical gels, organic gels, micellar surfactant solutions, emulsions, and foams. These fluids are loaded over a wide range of concentrations with particles of varying sizes and aspect ratios and are subjected to extreme mechanical and environmental conditions. We describe the settings of hydraulic fracturing (framed by geology), fracturing mechanics and physics, and the critical role that non-Newtonian fluid dynamics and complex fluids play in the hydraulic fracturing process.

Aqueous Glycosylation of Unprotected Sucrose Employing Glycosyl Fluorides in the Presence of Calcium Ion and Trimethylamine

We report a synthetic glycosylation reaction between sucrosyl acceptors and glycosyl fluoride donors to yield the derived trisaccharides. This reaction proceeds at room temperature in an aqueous solvent mixture. Calcium salts and a tertiary amine base promote the reaction with high site-selectivity for either the 3'-position or 1'-position of the fructofuranoside unit. Because nonenzymatic aqueous oligosaccharide syntheses are underdeveloped, mechanistic studies were carried out in order to identify the origin of the selectivity, which we hypothesized was related to the structure of the hydroxyl group array in sucrose. The solution conformation of various monodeoxysucrose analogs revealed the co-operative nature of the hydroxyl groups in mediating both this aqueous glycosyl bond-forming reaction and the site-selectivity at the same time.

Interaction of gums (guar, carboxymethylhydroxypropyl guar, diutan, and xanthan) with surfactants (DTAB, CTAB, and TX-100) in aqueous medium

The interaction of surfactants dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB), and p-tert-octylphenoxypolyoxyethylene (9.5) ether (TX-100) with guar (Gr), carboxymethylhydroxypropyl guar (CMHPG), diutan (Dn), and xanthan (Xn) gums has been studied employing conductometry, tensiometry, microcalorimetry, viscometry, and atomic force microscopy (AFM) techniques. Both weak and strong interactions were observed. CTAB interacted stronger than DTAB with the gums. The surfactant-gum interaction process was enhanced by the presence of borate ions in the solution; the borate ion itself also manifested interaction with the surfactants comparable with that of water-soluble polymers polyvinyl alcohol, polyoxyethylene, and so forth. Viscometric results supported configurational changes of the gum molecules by interaction with surfactants. The geometry of the pure gums and their CTAB interacted products in the dried states was ascertained from AFM measurements; spherical and prolate shapes were observed for pure gums, and distorted states were observed for their surfactant complexed species. Detailed topological features of these entities were ascertained.

Sorption of water vapor, hydration, and viscosity of carboxymethylhydroxypropyl guar, diutan, and xanthan gums, and their molecular association with and without salts (NaCl, CaCl2, HCOOK, CH3COONa, (NH4)2SO4 and MgSO4) in aqueous solution

Gums are routinely used in food industry, pharmacy and oil recovery process. In these uses, the hydrocolloids very often encounter interactions with salts at moderate to high temperature. Since they are normally employed in the form of solution and gel, their viscous or fluidity properties need detailed investigation. In the present work, properties such as water vapor adsorption of finely powdered carboxymethylhydroxypropyl derivatized guar (CMHPG) as well as xanthan (Xn) and diutan (Dn) gums, their hydration in solution, their viscosity behaviors, and salt effects on fluidity have been studied. The concentration domains for the existence of free and associated molecules in the studied solutions have been assessed from the viscosity results. The gums have been found to bind a fair amount of water from the vapor phase with them. In solution, they can interact and arrest a large amount of water in their folded configuration. Intrinsic viscosities of the gums in aqueous medium declined in the presence of salts. The activation energies for their viscous flow were moderate and comparable, and were dependent on their concentrations. From the power law relation and viscosity master curve behavior mostly two critical association states of the macromolecular dispersions were envisaged.