Study On The Regeneratable Gel Systems Of Degrated Glactomannan And Its Rheological Properties

In this paper, the degraded hydroxypropyl guar gum (DHPG) and degraded hydroxypropyl tara gum (DHPG) were synthesized from the endosperm of guar gum and tara powder, the rheological characteristics of DHPT solution was studied. The formation, regeneratable performance of borax cross-linked DHPT gel systems and the rheological properties of the gels before and after regeneration were investigated. The acidic zirconium crosslinker was prepared from the zirconium oxychloride and ethylene glycol, and the delayed crosslinking property was investigated. Main conclusions were obtained as follows:1) The optimized process conditions of HPG and HPT modified through etherification with propylene oxide(PO) were obtained. The influences of reaction temperature, reaction time, concentration of ethanol-water solution, dosages of NaOH and PO on viscosity and water-insoluble contents of products were illustrated. The optimized process for HPG was achieved:35%-40%(wt%) ethanol-water was used as reaction medium, of which the dosage was four times the weight of guar gum, the mass ratios of NaOH and PO to guar gum were 0.075:1 and 0.75:1 respectively, the alkalization lasted for 45min at 25℃while the etherification lasted for 3.5h at 55℃～60℃. The optimized process for HPT was achieved: 50%-55%(wt%) ethanol-water was used as reaction medium, of which the dosage was four times the weight of the tara powder, the mass ratios of NaOH and PO to tara powder were 0.05:1 and 0.75:1 respectively, the alkalization lasted for 45min at 25℃while the etherification lasted for 2.5-3.5h at 50℃～55℃. A series of different molecular weight DHPG and DHPT were obtained by hydrogen peroxide degradation method, their molecular weight decreased when the doage of H2O2 increased.2) DHPT solutions exhibited shear-thinning property, the relationship between apparent viscosity and shear rate corresponded to the Power Law Model, the relationship between zero shear viscosity and temperature corresponded to Arrhenius equation. The viscosity of DHPT solution had no significant change at pH=7-14, NaCl concentration had little effect on the viscosity of DHPT solutions.3) Stable gel system could be formed under certain composition of DHPT and borax and it possessed typical shear-thinning property, good visco-elasticity and thixotropy. The regeneratable borax cross-linked DHPT gel systems could be obtained by adjusting pH values, the rheological properties of these gels before and after regeneration had no significant change. The flow curves of the gels could be described by non-linear co-rotational Jeffreys model correctly, the calculated values and experimental data were in good agreement.4) The acidic zirconium crosslinkers with delayed action were obtained, and the cross-linked HPT gels with temperature tolerance over 100℃was prepared at acid condition. The influences of ethylene glycol concentration, crosslinking temperature, crosslinker preparation temperature and time on delayed crosslinking time were illustrated.The study in this paper was expected to provide rheological basis for the application of regeneratable degraded glactomannan gel systems and acidic oil field fracturing operation.