Research On The Rheological And Drag Reduction Properties Of Modified Xanthan Gum And Low Concentration Guar Solutions

Two kinds of modified xanthan gum (XG), hydroxypropyl xanthan gum (HXG) and cationic xanthan gum (CXG), were obtained under alkaline conditions in this paper. The factors of modified process were investigated to get appropriate reaction conditions. Spectroscopic methods (like FT-IR, NMR) were used to characterize the obtained samples. We also studied the rheological and micro-rheological properties, static sand carrier and drag reduction performance of HXG, CXG and CXG solutions. In addition, the changes of micro-rheological and rheological index were researched during crosslinking process of the low concentration guar gum. And the micro-rheokinetics model to describe the crosslinking process was established according to the micro-rheological experimental data. In order to have a good knowledge of the mechanism of static sand carrying, micro rheometer was applied to study the micro-rheological sand carrying performance both xanthan gum and guar gum systems. Finally, we attempted to learn the microstructure of aqueous HXG, CXG, XG, guar gum solutions and crosslinked guar gum gel with cryogenic field emission scanning electron microscopy (Cyro-FESEM). Main conclusions were achieved as follows:1) HXG and CXG were prepared from xanthan gum (XG) with propylene oxide and 3-chloro-2-hydroxypropyl trimethylammonium chloride under alkaline condition, respectively. The two modified products exhibited significantly higher viscosity under proper reaction conditions. The FT-IR, XRD, elemental analysis and 1H-NMR were employed to illustrate that HXG and CXG were desired product.2) Xanthan gum and its derivatives solutions were all shown shear-thinning properties, which could be fitted by nonlinear co-rotating Jeffreys model. The storage modulus G’and the loss modulus G" of HXG solutions were greater than those of XG solutions, and thixotropic and viscoelastic properties were more significant in HXG solutions. The HXG solutions possessed better performance of salt resistance, acid and alkaline stability, heat resistance and sand carrier. CXG solutions also had higher viscoelasticity and good thixotropy, but their tolerance to salt and acid were decreased.3) During the guar gum micro-rheological crosslinking process, the MVI (Macroscopic Viscosity Index) value changing with the amount of crosslinking agent and pH adjustment was studied to get the suitable dosage of crosslinking agent and pH adjustment. When the crosslinking temperature raised, the value of MVI decreased. This crosslinking process could be fitted by first order micro rheokinetics model at different temperatures.4) The viscosity changing with time was obtained during the crosslinking process of low concentration hydroxypropyl guar in shear flow field. The effcts of shear rate and temperamture on this crosslinking processs were achieved.5) The HXG and XG solutions reduced the pressure drop of both smooth and rough straight pipe, and the maximum drag reduction of 1 g·L-1 HXG and XG in smooth tube reached 72.8% and 68.1% respectively. Drag reduction rate was increased as the concentration increased. Compositing two kinds among xanthan gum, guar gum, and hydrophobic amphoteric cellulose derivatives (FAG-500) solutions with the total concentration of 1g/L, the drag reduction rate of complex system was higher than the single solution. Drag reduction rate of the xanthan gum and the long carbon chain alkyl amide amine oxide (LQ-FJ) compound was reduced.6) Xanthan gum and its derivative solutions had certain network structures. The network of HXG was further strengthened than that of XG There was obviously different in HXG solution and its sand carrying solution, indicating that the settlement of sand would break the HXG solution structure. Low concentration hydroxypropyl guar gum solution at low concentrations was linear structure. As the concentration increasing, molecules chain entangled each other in solution. When crosslinking agent was added to low concentration hydroxypropyl guar gum solution, the system formed weak gel and its structure was significantly enhanced.This paper is expected to provide rheology and drag the theoretical basis for the practical application of the system of xanthan gum and guar gel system in hydraulic fracturing.