Flow of viscoelastic surfactants through porous media

We compare the flow behavior of viscoelastic surfactant (VES) solutions and Newtonian fluids through two different model porous media having similar permeability: (a) a 3D random packed bed and (b) a microchannel with a periodically spaced pillars. The former provides much larger flow resistance at the same apparent shear rate compared to the latter. The flow profile in the 3D packed bed cannot be observed since it is a closed system. However, visualization of the flow profile in the microchannel shows strong spatial and temporal flow instabilities in VES fluids appear above a critical shear rate. The onset of such elastic instabilities correlates to the flow rate where increased flow resistance is observed. The elastic instabilities are attributed to the formation of transient shear induced structures. The experiments provide a detailed insight into the complex interplay between the pore scale geometry and rheology of VES in the creeping flow regime. © 2017 American Institute of Chemical Engineers AIChE J, 64: 773–781, 2018     

Application of pH-Responsive Viscoelastic Surfactant as Recyclable Fluid at High Temperature

A pH-responsive amphiphilic surfactant stearic amide 3-(N,N-dimethylamino)propylamide (SAA) was synthesized and served as a thickener in aqueous solution to construct a switchable viscoelastic surfactant fluid (VES fluid). The structure of SAA was studied by ¹H NMR, and the viscoelastic behavior of VES fluid was studied in detail by rheological measurements. The viscosity of this VES fluid can be switched reversibly from low to high immediately by adjusting system pH value. Even at high shear rate (170 s⁻¹) and high temperature (90 °C), excellent viscoelastic behavior of this VES fluid can be observed, which is a key performance for fracturing applications. Meanwhile, the recycled VES fluid can still maintain good pH-responsive behavior even after more than three cycles. These unique performances of this VES fluid not only enhanced our understanding of the transformation of wormlike micelles at high temperature, but also enriched a large potential of VES fracturing fluid in the development of oil and gas reservoirs.     

Study on rheology and thermal stability of mixed (nonionic–anionic) surfactant based fracturing fluids

Mixed surfactant systems have gained significant importance in the development of fracturing fluid due to polymorphism of self‐assembly structures that have combined properties of the surfactants in the mixture. In this article, a comparative study on the phase behavior and viscoelastic properties of mixed surfactant based fluids, prepared from Tween 80+NaOA/2‐ethyl hexanol/clove oil/water and Tween 20+NaOA/2‐ethyl hexanol/clove oil/water quaternary system is investigated in details. The viscoelastic surfactant (VES) based fluids prepared from the former system offered superior rheological properties than the latter system. The addition of 0.1% NaOH and 500 ppm ZnO nano‐particles in the VES fluids presented enhanced viscoelastic properties as concluded by static and dynamic rheological tests. Miscibility test indicated the miscibility of the VES fluids with water, unlike in the presence of diesel oil and satisfactory proppant suspension capabilities were exhibited by the developed fluids. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2177–2187, 2016     

压裂酸化用粘弹性表面活性剂溶液研究进展

粘弹性表面活性剂溶液的高表面活性及独特的流变特性可以作为理想的压裂、酸化、砾石充填等增产改造以及三次采油措施流体。详细介绍了粘弹性表面活性剂流体的组成、制备与表征方法,阐述了典型粘弹性表面活性剂流体流变特性研究现状;概述了粘弹性表面活性剂流体在压裂、酸化等增产措施中的应用进展,并指出了粘弹性表面活性剂流体矿场推广应用尚需解决的问题。     

Temporal Nature of Polymeric Flows Near Circular Pipe-Exit

Polymeric (viscoelastic) fluids have nonlinear mechanical properties and therefore the flow of a sufficiently elastic polymer solution may become irregular even at very low Re. Experimental evidences of these flow irregularities occurred near pipe exit at Re << 1 are presented here for Poiseuille flow of a highly elastic polymer solution. Although the Re is extremely low, the measured instantaneous pressures show turbulent-like fluctuations induced by elasticity of the fluid. Temporal nature of these fluctuations is analyzed in terms of Deborah number (De) that provides an appropriate measure for degree of nonlinearity in a polymeric flow.     

Application of erucyl dimethyl betaine sulfonate viscoelastic surfactant for optimization of acidizing operations in heterogeneous carbonate reservoirs

Reservoir heterogeneity is an important factor which should be considered for each operation in oilfields. Acidizing operation is performed to eliminate or reduce the damages of reservoirs. The dissolution of the minerals and rock texture in damaged areas is the main goal of acidizing. However, the existence of high permeable zones through flowing paths results in extra damages and fluid loss. Some additives could be added to the injected acid to avoid these undesirable phenomena. In this research, we added a Zwitterionic sulfonate surfactant to hydrochloric acid (HCl) solution and evaluated the rheological behavior of several compositions of acid-based viscoelastic surfactant (VES) solutions under various temperature and shear rates. The capability of optimum solution to plug the high permeable zone and divert the acid flow to low permeable zone is examined. The optimum solution was injected into a parallel sandpacked system with different permeabilities at various flow rates (1, 3 and 5 cc/min). It was observed that the injection rate of 3 cc/min has the most efficiency to reduce the heterogeneity. Besides the tendency of VES based solutions for altering wettability of rock to more water-wet condition is observed. The findings of this study can help the better understanding of practical application of VES in acidizing through heterogeneous reservoirs. Besides, effective parameters for such application are determined.     

清洁压裂液的研究与应用现状及未来发展趋势

黏弹性表面活性剂(VES)压裂液改变了传统聚合物压裂液生产操作方式,可以减少传统压裂液对地层的损害和污染,因此也被称为清洁压裂液。归纳了目前国内外现有的表面活性剂压裂液的体系组成、作用机理、研究现状及应用情况;基于矿场应用中存在的问题,对目前国内表面活性剂压裂液的发展趋势提出了一些建议。     

Viscoelastic properties of polyamic acid solutions—precursors of polyimides

The rheology of polyamic acid (PAA) solutions, precursors of polyimides used in microelectronic device applications, has been investigated by dynamic (oscillatory) shear flow measurements. Frequency dependent storage and loss moduli and dynamic viscosity were measured in the frequency range 10^?1 to 10³ rad/s at 23°C. The storage modulus G′ (ω) and loss modulus G″ (ω) exhibited quadratic and linear dependence in frequency at low frequencies respectively, the viscoelastic fluid behavior commonly predicted for polymer solutions from many molecular theories. At high frequencies both dynamic moduli become proportional to ω^2/3. The results show that PAA solutions are very high loss viscoelastic fluids, judging from the loss tangent values which far exceed unity. It is suggested that dynamic viscoelastic properties could be used to monitor the degree of imidization since there is a gradual change from viscoelastic fluids to soft viscoelastic solids to hard viscoelastic solids as PAA is converted to polyimides. Onset of non-Newtonian flow as shown on the frequency dependent dynamic viscosity was in the range 30 to 200 rad/s. The viscoelastic constants, zero-shear rate viscosity η_o and steady-state compliance J_e⁰, where also determined from the dynamic data and compared to previous steady shear flow results.     

A review of fracturing fluid systems used for hydraulic fracturing of oil and gas wells

Hydraulic fracturing has been used by the oil and gas industry as a way to boost hydrocarbon production since 1947. Recent advances in fracturing technologies, such as multistage fracturing in horizontal wells, are responsible for the latest hydrocarbon production boom in the US. Linear or crosslinked guars are the most commonly used fluids in traditional fracturing operations. The main functions of these fluids are to open/propagate the fractures and transport proppants into the fractures. Proppants are usually applied to form a thin layer between fracture faces to prop the fractures open at the end of the fracturing process. Chemical breakers are used to break the polymers at the end of the fracturing process so as to provide highly conductive fractures. Concerns over fracture conductivity damage by viscous fluids in ultra‐tight formations found in unconventional reservoirs prompted the industry to develop an alternative fracturing fluid called “slickwater”. It consists mainly of water with a very low concentration of linear polymer. The low concentration polymer serves primarily to reduce the friction loss along the flow lines. Proppant‐carrying capability of this type of fluids is still a subject of debate among industry experts. Constraints on local water availability and the potential for damage to formations have led the industry to develop other types of fracturing fluids such as viscoelastic surfactants and energized fluids. This article reviews both the traditional viscous fluids used in conventional hydraulic fracturing operations as well as the new family of fluids being developed for both traditional and unconventional reservoirs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40735.     

Effect of the contraction ratio upon viscoelastic fluid flow in three-dimensional square–square contractions

In this work we investigate the laminar flow through square–square sudden contractions with various contraction ratios (CR=2.4, 4, 8 and 12), using a Newtonian fluid and a shear-thinning viscoelastic fluid. Visualizations of the flow patterns were carried out using streak line photography and detailed velocity field measurements were performed using particle image velocimetry. The experimental results are compared with numerical predictions obtained using a finite-volume method. For the Newtonian fluid, a corner vortex is found upstream of the contraction and increasing flow inertia leads to a reduction of the vortex size. Good agreement is observed between experiments and numerical simulations. For the shear-thinning fluid flow a corner vortex is also observed upstream of the contraction independently of the contraction ratio. Increasing the elasticity of the flow, while still maintaining low inertia flow conditions, leads to a strong increase of the vortex size, until an elastic instability sets in and the flow becomes time-dependent at De≈200, 300, 70 and 450 for CR=2.4, 4, 8 and 12, respectively. At low contraction ratios, viscoelasticity brings out an anomalous divergent flow upstream of the contraction. For both fluids studied the flow presents a complex three-dimensional helical vortex structure which is well predicted by numerical simulations. However, for the viscoelastic fluid flow the maximum Deborah number achieved in the numerical simulations is about one order of magnitude lower than the critical Deborah number for the onset of the elastic instability found in the experiments.     

Cake filtration of suspensions in viscoelastic fluids

The fundamental framework for cake filtration of suspensions in viscoelastic media is extended to include the effects of polymer retention, including adsorption in the filter cake, polymer retention and elongational flow in the filter medium, which also undergoes compaction, and evaluation of polymer degradation in the filter cake and medium. Experimental data obtained in constant pressure filtration of starch suspensions in dilute aqueous polyacrylamide solutions confirmed the prediction of an enhanced apparent medium resistance R_ma and a reduced cake resistance α_R. Evaluations are presented of the contributions to the pressure drop due to enhanced normal stresses in elongational flow and to polymer retention (adsorption), and of the ratio of the particle size with and without adsorbed polymer in the cake. The analysis of the data points to high levels of polymer degradation during the flow of the polymer solution through the filter cake and medium.     

黏弹性表面活性剂压裂液的研究与应用进展

黏弹性表面活性剂压裂液是以黏弹性表面活性剂为主剂的清洁压裂液。黏弹性表面活性剂压裂液体系具有破胶后无残渣、携砂性好、滤失控制性能好等特点,但随着对环保问题的日益重视及钻井深度的不断增加,丰富黏弹性表面活性剂压裂液体系迫在眉睫。本文介绍了黏弹性表面活性剂压裂液的发展和应用。根据压裂液配方不同,将其分为常规黏弹性表面活性剂压裂液和非常规新型黏弹性表面活性剂压裂液,总结了不同种类的黏弹性表面活性剂压裂液的组成、耐温耐剪切等性能及应用情况。分析表明,降低成本、研制简单的配制工艺是常规黏弹性表面活性剂压裂液的主要发展方向;在油田进行大规模实际应用及得到更完善的体系是非常规新型黏弹性表面活性剂压裂液的主要发展方向。     

阴离子型VES压裂液在裂缝性油藏中的研究应用

裂缝性油藏中出现的天然裂缝会在水力压裂过程中发生剪切或者破坏等一系列现象,这导致了压裂液的滤失情况十分严重,进一步造成砂堵或者加砂困难等问题。针对裂缝性油藏中压裂液滤失严重的问题,通过研究阴离子型VES压裂液的性能来降低压裂液的滤失量。测试了VES压裂液的流变性能、耐温性能、粘弹性能、悬砂性能及破胶性能。研究表明,VES压裂液的耐剪切性很好,可以维持长时间的工作要求,在低剪切力下可以维持粘度的不变,在提高剪切速率时粘度会开始下降,在剪切速率得到回降后粘度又可以快速恢复;VES压裂液在60℃的地层中利用率最高,此温度下的粘度最大,弹性也最大,不可用于高于80℃的地层;VES压裂液支撑剂沉降速度很低悬砂性能很好,破胶很快且很彻底;这些优越的性能可以大量减少裂缝性油藏在水力压裂过程中压裂液的滤失量。     

Comparative studies of rheological properties of polyacrylamide and partially hydrolyzed polyacrylamide solutions

The present work is concerned with experimental results of rheological characteristics of polyacrylamide (PAM) and of partially hydrolyzed polyacrylamide (HPAM) (degree of hydrolysis up to 80%) in aqueous and aqueous/sodium chloride solutions with changing experimental conditions such as polymer concentration, temperature, solvent quality, and shear rate applied. It has been observed that the all‐aqueous and aqueous/NaCl solution of PAM and of HPAM exhibited the non‐Newtonian behavior with shear‐thinning and shear‐thickening areas. The onset of shear‐thickening at depends mainly on the degree of HPAM hydrolysis, as well as on solution concentration, temperature, solvent quality, and polymer molecular weight. Rheological parameters from power law (Ostwald de Waele model) and activation energy of viscous flow (E_a) are determined and discussed. The changes in apparent shear viscosity during aging of solutions of PAM and HPAM are also described. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2235–2241, 2007     

Laminar dispersion of polymer solutions in helical coils

In the present study the step response experiments were carried out with power law fluids in two helical coils to examine the suitability of axial dispersed plug flow model in describing the laminar dispersion of non-Newtonian fluids in helical coils. The ranges of variables covered are 10 ≤ λ ≤ 100,0.01 ≤ N_Regen ≤ 2.5,0.001 ≤ N_De ≤ 0.77 and 0.035 ≤ τ ≤ 1.33. It is found that coiling results in reduced dispersion to that in a straight tube.     

Viscoelastic sol–gel state of the chitosan and alginate solution mixture

The rheological behavior of chitosan/alginate solutions was investigated in relation to gelation and polyelectrolyte complex (PEC) formation. Before mixing, the chitosan and the alginate solutions were both homogeneous fluids. However, heterogeneity developed after mixing, accompanied by a serious increase of viscosity. To determine the sol–gel state of the solutions, the viscoelastic variables, such as the dynamic storage modulus (G′) and loss modulus (G″), the loss tangent, and the viscoelastic exponents for G′ and G″, were obtained. Depending on the concentration, the chitosan/alginate solutions revealed unexpected rheological behavior. At a polymer concentration of 1.0 wt %, the chitosan/alginate solution was in a viscoelastic gel state, whereas, at higher concentrations, viscoelastic sol properties were dominant. A viscoelastic gel state for the chitosan/alginate solution was induced based on the weak formation of fiber‐shaped precipitates of a PEC at a low polymer concentration. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1408–1414, 2007     

Performance optimization for the viscoelastic surfactant using nanoparticles for fracturing fluids

Abstract

In order to optimize the viscoelastic properties and temperature-resistance for the sodium 2,2'-(propane-1,3-diylbis(stearoylazanediyl))diethanesulfonate Gemini viscoelastic surfactant, the effects caused by the addition of nanoparticles were investigated. The viscous and rheological behaviors and microstructures of surfactant solutions with/without magnesium oxide (MgO) or lipophilic silicon dioxide (SiO₂) nanoparticles were studied using rheometer and field emission scanning microscopy electron microscopy (FESEM). The experimental results showed that the addition of optimal nanoparticle mass fractions significantly increases the viscoelastic properties for the viscoelastic micelle solutions at 90?°C. The enhancements in viscoelastic properties are ascribed to the formation of network structures due to the addition of nanoparticles. The use of nanoparticles showed promising improvements to be applied for fracturing fluids at high temperatures.     

Synthesis and application of nonionic polyacrylamide with controlled molecular weight for fracturing in low permeability oil reservoirs

Nonionic polyacrylamide (NPAM) with controlled molecular weight was successfully synthesized as a gel fracturing fluid by aqueous solution polymerization. The effects of the monomer concentration, initiator concentration, reaction time, feeding temperature and reaction temperature on the molecular weight were systematically investigated through single‐factor and orthogonal experiments. The NPAM molecular weight can be controlled by adjusting these factors. The decisive factor is the acrylamide concentration, whereas the initiator concentration and feeding temperature are secondary factors. These synthetic NPAMs can be crosslinked with zirconium acetate to produce a gel fracturing fluid for use in low permeability oil reservoirs. Gel fracturing fluids based on synthetic NPAMs have high shear resistance, low filtration performance, easy gel breaking performance, good proppant carrying capability and low core damage capability. By adjusting the NPAM or crosslinker concentrations, the gel fracturing fluid can be adapted for use in low permeability oil reservoirs for a wide temperature range (60–120°C). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41637.     

一种经济型清洁压裂液配方研究与性能评价

粘弹性表面活性剂(Viscoelastic surfactant,下文简称VES)压裂液与传统聚合物压裂液不同,可消除残余聚合物对支撑剂充填层的堵塞,并能有效提高导流能力,减少对地层的损害及污染,压后油气产量比使用传统压裂液有显著提高。介绍了VES压裂液的原理及配方设计原则。通过室内试验确定了一种经济型VES压裂液的配方,并对其性能进行了相关评价。     

Analysis on the apparent slip and depleted layer of polymer flow in narrow-bore capillaries

Polymer solutions flowing through small-diameter capillaries of which length scale is much larger than that of polymers were experimentally demonstrated to have the enhanced flow rate as compared to in bulk flow. Thisapparent slip phenomenon was analyzed by obtaining theslip velocity and concentrationdepleted layer thickness. Hydrolyzed polyacrylamide (HPAM) of highly flexible polymer and Xanthan of rigid rodlike polymer were made to flow through stainless steel capillaries having the diameter range of about 100 to 250 μm. The results showed that both slip velocity and depleted layer thickness decreased markedly with increasing polymer concentration. This behavior can be interpreted as being due to the reduction of diffusion coefficient and flexibility of polymer chains as the concentration is increased. The depleted layer thickness of HPAM was much larger than the polymeric length scale and was shown to increase with increasing wall shear stress. This is considered as an evidence of thestress-induced diffusion of polymer chains being a dominant factor for the apparent slip of flexible polymer solution. On the other hand, the depleted layer thickness of Xanthan solution was almost constant with the wall shear stress, which can not be explained by the stress-induced diffusion mechanism alone.