Xiaohui Qiu

Intrinsic Rheo-Kinetics on Gelation Process of Hydrophobic Amphoteric Cellulose

Micro-rheological properties including elasticity index (EI) and solid liquid balance (SLB) of gelation process of hydrophobic amphoteric cellulose solution at different temperatures and crosslinker concentrations were investigated by optical micro-rheometer in this work. During the crosslinking gelation process, EI appears a two-stage rise, and SLB first increases to maximum and then decreases to constant. According to EI curves, the gelation process can be divided into two stages. Intrinsic rheo-kinetics equations were first established to characterize the two-stage crosslinking process. The simulated values by the novel intrinsic rheo-kinetic models were in good agreement with experimental data and the model parameters were well-defined and of reasonable significance. GRAPHICAL ABSTRACT

Rheological properties of water-soluble cross-linked xanthan gum

ABSTRACT Water-soluble crossslinked xanthan gum (CXG) was prepared from xanthan gum (XG) and epichlorohydrin under alkaline condition by ethanol solvent method. Rheological properties and heat resistance performance of different concentrations of aqueous XG and CXG solutions were investigated. The results showed that the apparent viscosity of 4 g · L−1 CXG solution was 2.57 times that of 4 g · L−1 XG solution. The storage modulus G′ and the loss modulus G″ of CXG solutions were greater than those of XG solutions, and viscoelastic and thixotropic properties were more significant in CXG solutions. At 80°C, these two solutions were sheared at 170 s−1 for 90 minutes, the reserved viscosity was 32.30 and 62.15 mPa · s for XG and CXG solutions, respectively. The heat resistance performance of CXG solution was better than that of XG solution. Nonlinear co-rotational Jeffreys model could be applied to describe the flow curves of XG and CXG solutions correctly, and the calculated values were in good agreement with the experimental data. GRAPHICAL ABSTRACT

Intrinsic Crosslinking and Gel-Breaking Rheokinetics of CMHEC/CTAB Systems

The intrinsic rheokinetics of carboxymethyl hydroxyethyl cellulose and cetyltrimethyl ammonium bromide (CMHEC/CTAB) synergistic fracturing fluid in static crosslinking and gel-breaking processes were studied in this work. Microrheological properties including solid–liquid balance (SLB) and elasticity index (EI) during the static crosslinking and gel-breaking processes were obtained. The effects of temperature on the crosslinking process, concentration of gel-breaker (ammonium persulfate), and temperature on the gel-breaking process were investigated. The novel intrinsic crosslinking and gel-breaking rheokinetics equations were established, respectively. The results show that the crosslinking process can be divided into two stages, and the intrinsic crosslinking rheokinetics equation can well describe EI curves during the static crosslinking process at different temperatures. The EI curves during the gel-breaking process can be well described by the intrinsic gel-breaking rheokinetics equation. The parameters for these two rheokinetics equations are well-defined and reasonable. GRAPHICAL ABSTRACT

Rheokinetic study of gel-breaking process of xanthan gum solution

ABSTRACT The dynamic rheological behavior of xanthan gum (XG) during the gel-breaking process was studied in this work. Both experimental and numerical simulations were adopted to investigate the effects of temperature and added salt on the gel-breaking process. The results showed that the gel-breaking reaction is slowed down by the added salt, while temperature has a positive influence on the chemical degradation of XG. The novel rheokinetics equations were established to describe the gel-breaking process of XG and the simulated values are in good agreement with experimental data. The changes of the model parameters with respect to temperature and added salt are consistent with the experimental results obtained with rheometer, which verifies the feasibility of the established rheokinetics equations for characterizing the gel-breaking reaction of XG. GRAPHICAL ABSTRACT

Rheokinetics of the gelling process of water-soluble STMP-modified carboxymethyl hydroxyethyl cellulose

ABSTRACT To improve the viscosity of carboxymethyl hydroxyethyl cellulose (CMHEC) solution and broaden its application, sodium trimetaphosphate (STMP) was used to modify CMHEC to obtain water-soluble STMP-CMHEC for the first time. The STMP-CMHEC solution shows better viscous performance than CMHEC solution. For the concentration of 0.5% (wt%), the viscosity of STMP-CMHEC solution is 2.6 times higher than that of CMHEC solution. To be applied in fracturing fluids, STMP-CMHEC solution was further cross-linked with organic zirconium. The changes of viscosity and viscoelasticity modulus with time in the cross-linking process were studied. The effects of shear rate and temperature on the gelling process were investigated. The four-parameter cross-linking rheokinetics equation could describe the viscosity–time curves under different shear rates. GRAPHICAL ABSTRACT

Rheological Properties and Crosslinking Rheo-Kinetics of CMHEC/CTAB Synergistic Systems

Aiming at synergistic interaction between carboxymethyl hydroxyethyl cellulose (CMHEC) and cetyltrimethyl ammonium bromide (CTAB), mixtures of CMHEC and CTAB solutions were investigated, employing relative viscosity and rheological measurements. The effects of mass ratio of CMHEC and CTAB solutions, temperature, and polysaccharide concentration on relative viscosities of CMHEC/CTAB systems were studied. Rheological method was used to study rheo-kinetics of the isothermal crosslinking process for CMHEC/CTAB synergistic fracturing fluid, and the novel crosslinking rheo-kinetics equation was established. The results showed the strong synergism between CMHEC and CTAB, resulting in a higher relative viscosity, storage modulus G′, and loss modulus G″ than that of separate ones. CMHEC/CTAB systems behave as pseudoplastic fluids with considerable thixotropy and viscoelasticity, and the flow behavior can be well described by Carreau−Williamson model. The crosslinking rheo-kinetics equation can well describe the isothermal crosslinking process at different shear rates. The model parameters are well-defined and reasonable. GRAPHICAL ABSTRACT

Rheological properties of hexadecyl dimethyl amine modified carboxymethyl hydroxyethyl cellulose solutions and its gelling process

ABSTRACT To obtain a new fracturing fluid viscosifier, hexadecyl dimethyl amine was used to modify carboxymethyl hydroxyethyl cellulose (CMHEC) to obtain a product called HD-CMHEC with high viscosity. The rheological properties of HD-CMHEC solutions and CMHEC solutions were studied. For the concentration of 0.3%, the viscosity of CMHEC and HD-CMHEC solutions is, respectively, 19.0 mPa · s and 73.6 mPa · s, respectively. The viscosity of HD-CMHEC solution increases 2.8 times than before. The thixotropy and viscoelasticity of HD-CMHEC solutions become stronger. As a typical viscoelastic fluid, HD-CMHEC solutions show better rheological performance than that of CMHEC solutions. The gelling process of HD-CMHEC solutions under steady shear was studied in detail. The concentrations of HD-CMHEC solutions, shear rates, and crosslinking agent were investigated. Viscosity versus time curves during the crosslinking process were obtained. The four-parameter crosslinking rheokinetics equation can describe the gelling process of HD-CMHEC solutions under different conditions well. Study on the gelling process of HD-CMHEC solutions under steady shear contributes to the understanding of gel formation, and provides theoretical guidance for exploration and exploitation of the system. GRAPHICAL ABSTRACT

Rheology and high-temperature stability of novel viscoelastic gemini micelle solutions

ABSTRACT To broaden the application of clean fracturing fluid based on surfactant, a gemini cationic C25-tailed surfactant, called FL-25, was synthesized. FL-25 can form a wormlike viscoelastic fluid in aqueous solution without adding any organic or inorganic salts. The rheological properties and thermal stability of the novel gemini micelle solutions were further investigated. The results show that the gemini micelle solution possesses viscoelasticity, thixotropy, and shear-thinning properties. The apparent viscosity of the viscoelastic gemini micelle solution at a shear rate of 170 s−1 remains approximately 69 mPa · s at 110°C for 90 minutes, showing good high-temperature-resistance property. FL-25 may be a novel gemini surfactant applied in clean viscoelastic surfactant fracturing fluids in the oil and gas field. GRAPHICAL ABSTRACT

Rheological and microrheological characterization of a novel amphoteric xanthan gum

ABSTRACT A novel amphoteric xanthan gum (AXG) containing anionic carboxyl groups and cationic quaternary ammonium substituents was prepared from xanthan gum (XG) and 3-chloro-2-hydroxypropyltriethanolammonium acetate. The rheological and microrheological properties of AXG and XG solutions were studied in this work. The rheological results showed that the apparent viscosity of the 0.4% AXG solution was 5.26 times that of the 0.4% XG solution, and the AXG solution exhibited more obvious thixotropy and much stronger viscoelasticity than the XG solution. Both experiment and numerical simulations were adopted to investigate the gel-breaking process of the AXG solution, and the rheokinetics equations can well describe the evolution of complex viscosity. Moreover, the optical microrheology method was also adopted to investigate the microrheological behavior of AXG and XG solutions. The microrheological results showed that the AXG solution exhibited higher viscosity index at zero shear and a more obvious solid-like behavior than the XG solution. Good agreement is found when comparing the results obtained from microrheology to classical rheology, which verifies the feasibility of the microrheology method for measuring the solution properties, especially some properties not well described by the current rheological approach. GRAPHICAL ABSTRACT

A comparison of rheokinetics on static and shear crosslinking processes of xanthan gum

ABSTRACT The crosslinking process of xanthan gum was studied under static and shear conditions. Conventional rotational rheometer was adopted to study the shear crosslinking process, and the static crosslinking process was monitored using an optical microrheometer without physical contact between the instrument and the sample. Both experiment and numerical simulation were adopted to compare the two gelation processes at different temperatures. The results showed that the effects of temperature on static and shear crosslinking processes of xanthan gum have the same trend and the rheological curves of the two gelation processes are similar in shape. The same rheokinetics equations were established to describe the two gelation processes and the simulated values are in good agreement with the experimental data. The changes of the model parameters with respect to temperature are quite similar for both the gelation processes, which verifies the feasibility of the microrheology method for measuring the static crosslinking reaction. GRAPHICAL ABSTRACT Static and shear crosslinking processes of xanthan gum were studied by optical microrheology and classical rheology, respectively. Both experiment and numerical simulation were adopted to compare the two gelation processes. Good agreement was found when comparing the results obtained from microrheology to classical rheological measurements, which verifies the feasibility of the microrheology method for measuring the static crosslinking reaction.