Liwei Wang

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

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

Analysis of Fracturing Fluid Microstructure by Scanning Electron Microscope

The analysis experiment methods of fracturing fluid were many and varied, but microstructure analysis of fracturing fluid had not appropriate experimental method. Fracturing fluid sample was feasible after sample preparation including high-pressure freezing, vacuum freezing transport, freeze break etching, sublimation, ion sputtering spraying in turn, which could be observed under high vacuum. Using scanning electron microscopy (SEM) analysis with high vacuum conditions, different kinds of fracturing fluid microstructure in three basic conditions were studied. The experimental results showed that fracturing fluid had liquid, gel, and gel breaking liquid three base states with preparing, cross-linking, and breaking three processes, the corresponding microstructure changes from line to net to linear–net mixed structure. Fracturing fluid types, the concentration of thickener, and other factors directly affected the microstructure of fracturing fluid: Gel had different network structure and network density. Gel with low concentration thickener had low viscosity, bad gel hang, easy gel breaking, and gel corresponding microstructure was more sparse; experiment observed surfactant fracturing fluid’s micelles were linear structure and had layer-linear mixed existence state. Microstructure studied establish the connection between fracturing fluid microstructure and macro-performance to provide experimental methods and evidence for analysis and improving fracturing fluid formula.

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.