CO2泡沫压裂液粘弹性与触变性的表征研究

文章针对低效油气藏存在低压、水敏等问题,开发了CO₂泡沫压裂液技术。该压裂液以气液两相组成,外相为液态交联瓜尔胶,内相为气态二氧化碳。实验仪器为控制应力流变仪,分析了CO₂泡沫压裂液的流变学特性,包括泡沫流体的粘弹性和触变性,并采用粘弹-触变性本构方程描述典型的泡沫压裂液流体的触变环,采用广义Maxwell粘弹性本构方程描述泡沫压裂液流体的粘弹性。泡沫压裂液同时具有剪切变稀、粘弹性和触变性,采用5个参数粘弹触变性本构方程可描述典型的泡沫压裂液流体的触变环,用广义Maxwell粘弹性本构方程可描述泡沫压裂液流体的粘弹性,模型计算值与实验值吻合良好,本构方程具有良好的适应性。     

聚丙烯酰胺-Cr3+凝胶的结构与性能关系

延迟交联对油田深部调剖至关重要。利用聚丙烯酰胺与乙酸铬交联剂反应制备延迟交联体系,成胶之后采用HAAKE RS600型流变仪、填充砂管驱替实验测定聚丙烯酰胺凝胶的黏弹性、屈服性、触变性及封堵性能,采用环境扫描电镜(ESEM)观察凝胶的微观网络结构,并考察聚丙烯酰胺质量分数的影响。结果表明,聚丙烯酰胺-Cr3+凝胶是一种以弹性为主的剪切变稀型黏弹性体,随着聚丙烯酰胺质量分数的增大,凝胶的黏弹性增强,屈服值、正触变环面积和应力过冲值也增大,且凝胶对多孔介质的封堵性能增强。聚丙烯酰胺质量分数增大,凝胶的微观交联密度增大,网络结构增强,且由孔径较大的稀疏的网络交织增强为孔径较小的密集层状叠加的空间网络结构,表明聚丙烯酰胺凝胶的宏观性能与其微观结构密切相关。     

水泥浆触变性评价新方法的试验研究

分析了利用水泥浆触变性能解决现场问题的本质,在此基础上提出了采用静胶凝强度发展速率以及剪切前后胶凝强度差值来评价水泥浆触变性的新方法,并对其进行了试验研究.研究表明,采用静胶凝强度发展速率与剪切前后胶凝强度差值,能够比较直观地反映水泥浆触变性能的优劣,水泥浆的静胶凝强度发展速率越快,剪切前后胶凝强度变化越大,说明水泥浆触变性能越好;反之,水泥浆触变性能越差.利用新方法对水泥浆触变性能进行评价,得到的试验结果与现行的滞后环总能量法的结果是一致的.     

粘弹性颗粒驱油剂的流变特性

粘弹性颗粒驱油剂B-PPG是一种全新的驱油剂,具有部分交联、部分支化的分子结构,分散于水中形成非均相的B-PPG悬浮液。采用稳态剪切和动态振荡实验,研究了不同质量分数、不同交联度的B-PPG在不同矿化度盐水中的流变特性,并分析其产生机理。结果表明,B-PPG悬浮液具有优异的粘弹性、耐盐性和增粘性。随着B-PPG交联度的增加,B-PPG悬浮液粘度呈下降趋势,B-PPG悬浮液粘性与弹性模量交点处频率(Fc)逐渐趋向低频;高矿化度使部分水解聚丙烯酰胺(HPAM)溶液的弹性减弱,而对B-PPG悬浮液模量影响较小,表明B-PPG较HPAM具有更优异的耐盐性;随着B-PPG质量分数的增大,B-PPG悬浮液线性粘弹区范围增大,且粘度明显增大,B-PPG悬浮液更加偏离牛顿流体,Fc值逐渐趋向低频;通过对其动态振荡曲线的线性拟合数据发现,B-PPG悬浮液表现出弱凝胶特性。     

纳米SiO2复合润滑脂流体的触变效应

以10~50 nm SiO₂制备了分别以二甲基硅油、NBR硅油以及PAO-40为基础油的复合润滑脂,考察了其流变与触变性。采用Casson模型,拟合所得到的复合润滑脂流变曲线表明,纳米SiO₂的比表面积越小,所制备的复合润滑脂的屈服应力和表观黏度越大。比表面积大的纳米SiO₂制备的复合润滑脂易形成均相非触变流体,升高温度将会显著诱导负触变环的产生,从而降低润滑脂稳定性。在高剪切速率时,在3种制备的复合润滑脂中,纳米SiO₂-二甲基硅油复合润滑脂的黏温性能最佳。这种复合润滑脂独特的触变效应是由其内部SiO₂纳米粒子絮状微结构和黏滞运动所造成。     

VES自转向酸破胶问题研究

VES自转向酸具有变黏、缓速、降滤、无伤害的特征,其分流转向技术是近年来发展的实现大井段、多层系储层改造新方法,在国内外分流转向施工中得到了广泛应用。针对使用VES自转向酸施工后需要很长返排期才能达到最大产能、体系存在破胶困难的问题,本文模拟了不同剪切速率以及处于不同区域的VES流体的破胶性能。测试结果发现,具有黏弹性的VES流体的破胶速率及破胶程度与剪切速率有关,且存在临界剪切应力——流体的屈服应力;在中、高剪切速率下VES流体能快速完全破胶,而在低剪切或不剪切的环境下,VES流体破胶很困难;处于多孔介质内的黏弹性流体破胶同样非常困难,但可以通过增加后置互溶剂用量,提高VES流体的破胶效果,减小对储层的伤害。     

微观液滴分布对含蜡原油乳状液流变性的影响

通过显微镜观察并拍摄原油乳状液的微观结构图像,研究了乳状液体系分散相液滴大小及分布规律,以及微观液滴分布对乳状液体系流变性的影响机理。W/O型原油乳状液中含水率增加,引起内相液滴个数增多,小液滴所占的比例减小,相对大的液滴所占的比例增大;搅拌转速的增大,使体系内相液滴个数增多,平均液滴直径减小。通过测试在固定搅拌条件下制备的不同含水率的3种含蜡原油乳状液在原油凝点附近温度屈服特性和触变性等流变特性,可以发现随含水率的增大,乳状液体系屈服应力增大、触变性增强,且含水率越高,变化的趋势越明显。通过测试不同搅拌转速下制备的含水率为30% 的原油乳状液在原油凝点附近温度的触变性,可以看出随搅拌转速的增大,体系经受同等剪切速率剪切时对应的剪切应力增大、触变性增强。进一步建立了屈服应力与测试温度、含水率之间的关系式,其平均相对误差为9.83%。     

芥酸酰胺丙基二甲基叔胺改性纤维素溶液的 流变性能与交联性能

为了改善纤维素溶液的增稠能力和交联性能,合成了一种新型疏水醚化改性剂(3-氯-2-羟丙基芥酸酰胺醋酸铵),并采用该改性剂对羧甲基羟乙基纤维素(CMHEC)进行疏水改性,首次制得了芥酸酰胺丙基二甲基叔胺疏水改性纤维素(ED-CMHEC),研究了CMHEC和ED-CMHEC溶液的流变性能(表观黏度、流动曲线、触变性和黏弹性)和交联性能。研究结果表明,改性后ED-CMHEC溶液的表观黏度得到显著提升并表现出更显著的触变性与黏弹性。质量分数0.3%的CMHEC和ED-CMHEC溶液在30℃、170 s~(-1)的表观黏度分别为18 mPa·s和71mPa·s,后者较前者提高了2.94倍。不同质量分数(0.3%数0.5%)的CMHEC和ED-CMHEC溶液均表现出剪切变稀性质,其流动曲线可用Cross模型进行描述。有机锆交联剂FAC-201加量为0.2%时,质量分数0.3%ED-CMHEC溶液交联形成凝胶的黏度是改性前的2.4倍,表现出更强的交联性能。图9表4参22     

P（MAA/AMPS/DMAM/NVCL）稠化剂的制备及其交 联过程流变性能分析*

为获得性能优良的压裂液体系,以α-甲基丙烯酸(MAA)、2-丙烯酰胺基-2-甲基丙磺酸(AMPS)、N,N-二甲基丙烯酰胺(DMAM)、N-乙烯基己内酰胺(NVCL)为主要原料,通过溶液聚合法制备了新型四元聚合物稠化剂,并研究了该聚合物溶液的流变性能;以有机锆为交联剂制备交联凝胶,考察不同因素(交联比、剪切速率、温度)对交联过程流变动力学的影响。研究结果表明:在温度25℃、剪切速率170 s~(-1)下,质量分数0.6%的聚合物溶液的表观黏度为100 m Pa·s,增黏效果好,具有明显的剪切变稀性,其流动曲线可用Cross模型进行表征;质量分数0.6%的聚合物溶液与交联剂在交联比100∶0.6下的交联效果良好,凝胶黏弹性较高;聚合物溶液交联过程可用四参数交联流变动力学方程进行表征,为该四元聚合物压裂液的应用提供了流变学研究基础。图14表4参19     

基于滞回环的含蜡原油触变模型评价

触变性是含蜡原油的一个重要流变特性,对输油管道停输再启动过程的水力特性及安全性至关重要。通过实验,研究了4种含蜡原油在剪切速率先呈线性增大后呈线性减小这一循环加载条件下的滞回环特性。利用最小二乘原理,分别对剪切速率循环一次得到的单一滞回环和剪切速率变化率不同的多个循环得到的多个滞回环进行了拟合。用平均偏差作为统计指标,对8个触变模型进行了评价。结果表明,基于Cheng的含蜡油品中存在完全可逆和完全不可逆两类结构,在Houska模型的基础上建立的模型最适合于描述含蜡原油的滞回环特性。     

有机凝胶调剖剂强度的剪切恢复性能研究

采用动态剪切实验研究了两种有机凝胶类调剖剂强度的剪切恢复性能,通过测定不同条件下凝胶体系的储能模量\耗能模量和相位角的变化,分析了在聚交比一定的条件下,聚合物浓度、温度以及交联剂类型对凝胶剪切后强度恢复性能的影响。结果表明:在一定的应力下,随着聚合物浓度的增加,凝胶的成交点频率向低频移动;相同聚合物浓度和放置时间下,有机金属交联型调剖剂的强度大于有机酚醛交联型调剖剂;同种凝胶体系,在聚交比一定的条件下,浓度高时体系强度的剪切恢复性能好;对于两种凝胶体系来说,温度升高使得体系的剪切恢复性能下降;有机金属交联的凝胶体系剪切恢复能力高于有机树脂交联的凝胶体系。     

A Study on the Thixotropy of Egyptian Bentonite Suspensions

The rheology behavior of water bentonite suspensions has been studied through recording the viscosity measurements to study the thixotropy of the suspensions using local Egyptian bentonite at 5.0%, 6.40%, and 7.5.0% concentrations in the a presence of different salt concentration as 0.0 M, 0.01 M, and 0.1 M NaCl according to API stander, rheological data was calculated by viscometer, deriving first the D0 curve, from 600 to 3 rpm, followed by a typical thixotropic loop, getting the U curve from 3 to 600 rpm, and then the D curve from 600 to 3 rpm. Three rheograms have been derived for each suspension after intensive preshearing, from high to low, from low to high, and from high to low shear rates. Positive thixotropy is observed for all suspensions at 0.0 M and 0.01 M but not at 0.1 M salt concentrations. Thixotropic indexes computed from the normal thixotropic loop, low to high to low shear rates, have been computed and vary from positive to negative. The higher the bentonite concentration, the higher the index for the suspensions with no salt, while in the presence of salt, variations of the thixotropy index are obtained with the degree of variation dependent on bentonite concentration and salt concentration The suspension with no salt and 0.01 M salt exhibited thixotropy, estimated from the D0-U curves, while the 0.1-M suspensions showed no thixotropy. Thixotropy indices vary and depend on bentonite type and concentration and on the presence and amount of salt.     

六参数含蜡原油触变模型

含蜡原油在较低温度下具有典型的触变特征,触变模型是含蜡原油输送管道再启动数值模拟的基础。在分析现有触变模型的基础上,结合含蜡原油的特性以及悬浮体系流变学的相关理论,提出了一个适用于含蜡原油的包含6个参数的黏塑性触变模型,并利用基于剪切率阶跃方法测试的触变数据对该模型进行了检验。结果表明,该模型对触变数据的拟合效果优于目前常用的包含8个参数的Houska模型,与12个参数的双结构参数模型相当。与Houska模型和双结构参数模型相比,所提出的六参数模型因拟合参数少且状态方程形式较为简单,通过优化算法拟合确定的触变参数定性上更为合理,更适用于含蜡原油管道停输再启动数值模拟。     

Formulation and Comparative Study of Rheological Properties of Loaded and Unloaded Ethanol-Based Gel Propellants

The current trend in the area of highly energetic storable liquid rocket propellant research is to develop environmentally friendly gelled/metallized systems and to explore the feasibility of their application in rocket engines. The idea stems from the fact that the conversion of a conventional liquid propellant to a gelled state and its subsequent metallization has the potential to significantly enhance the performance and density-specific impulse. The gelation of liquid fuels could be induced at a critical gellant concentration of as low as 8 wt% for the pure ethanol case and as low as 4 and 6 wt% for metallized ethanol depending on the metal type. Furthermore, the gel formed should be thixotropic. Metallized gels using 20 wt% Al and B metal powders could also be formulated. These metallized (Al and B) ethanol gel systems showed a reduction in the critical gellant concentration depending on the degree of metallization. The rheological properties of metallized and nonmetallized ethanol gels using methyl cellulose (MC) as a gelling agent at different ambient temperatures (283.15, 293.15, 303.15, 313.15, and 323.15 K) were experimentally investigated in this study. The gel fuels were rheologically characterized using a rheometer at shear rates ranging from 1 to 12 s^?1 and 1 to 1,000 s^?1. Metallized and nonmetallized ethanol gels were found to be thixotropic in nature. The apparent viscosity and yield stress (for shear rate range 1 to 12 s^?1) of gels were observed to significantly decrease at higher ambient temperatures and as the gellant and metal particle concentrations decreased. The thixotropic behavior was found to be a strong function of the Al and B metal particle concentration for all test temperatures at shear rate ranges from 1 to 12 s^?1 and 1 to 1,000 s^?1. It was also a function of the MC concentration at a shear rate range of 1 to 1,000 s^?1.     

工业氯化钙加重胍胶压裂液体系研究与现场试验

为了解决现有加重压裂液体系成本高及加重密度低等问题,采用工业氯化钙作为加重剂,研发了一种低成本加重压裂液技术。在分析硼交联剂在氯化钙胍胶基液中交联受阻机理的基础上,制备了耐高浓度氯化钙溶液的交联剂,可在低pH值环境下使高浓度氯化钙溶液和胍胶基液形成交联冻胶。工业氯化钙加重胍胶压裂液具有加重密度高、基液黏度低和耐温耐剪切性能良好等特点,在温度140 ℃、剪切速率100 s–1条件下剪切2 h后,冻胶黏度大于100 mPa·s。现场试验表明,超深井采用氯化钙加重胍胶压裂液进行压裂施工,施工压力可降低10～15 MPa。研究表明,氯化钙加重胍胶压裂液性能可靠,能够降低超深高应力储层改造施工压力,提高压裂效果,具有现场推广应用价值。      

Modeling the viscoelasto-plastic behavior of waxy crude

Waxy crude oil exhibits complex rheological behavior below the pour point temperature, such as viscoelasticity, yield stress, and thixotropy, owing to the formation of a three-dimensional spongelike interlock network structure. This viscoelasto-thixotropic behavior is an important rheological behavior of waxy crude oils, determining the flow recovery and safe restart of crude oil pipelines. Up to now, the thixotropic models for waxy crude have been all viscoplastic models, without considering the viscoelastic part before the yield point. In this work, based on analyzing the variation of the elastic stress and viscous stress in the Mujumbar model, a new viscoelasto-plastic model is proposed, whose shear stress is separated into an elastic component and a viscous component. The elastic stress is the product of the shear modulus and elastic strain; the shear modulus is proportional to the structural parameter. For the elastic strain, we followed the line of Zhu and his coauthors and assumed that it may be expressed by an algebraic equation. The model is validated by stepwise shear rate tests and hysteresis loop tests on Daqing and Zhongyuan waxy crude. The results show that the model’s fitting and predictive capability is satisfactory.     

瓜胶压裂液携砂微观机理研究

通过对瓜胶压裂液进行静态支撑剂沉降实验、动态黏弹性测试、屈服应力测试、分子结构表征,研究了瓜胶压裂液的宏观性能、分子结构与压裂液携砂性能间的关系。支撑剂沉降实验表明,压裂液黏度的变化与支撑剂沉降速率呈非线性关系,用黏度指标很难准确表征压裂液的携砂性能。动态黏弹性测试表明,压裂液损耗模量的增加有利于降低支撑剂沉降速率,而储能模量的大幅度提高赋予流体弹性特征,这才是支撑剂能够长时间保持均匀悬浮状态的根本原因。压裂液微观结构分析表明,压裂液基液具有杂乱、松散、多孔洞的网络堆砌结构,而交联压裂液具有均匀、紧密的整体堆砌结构,该结构赋予交联压裂液弹性,使其携砂能力发生本质变化。     

W/O型含蜡原油乳状液胶凝体系的屈服特性

在恒定剪切应力和剪切应力线性增加2种加载模式下,研究了油包水（W/O）型含蜡原油乳状液胶凝体系在凝点温度附近的屈服行为。以原油乳状液胶凝体系的屈服应变、屈服剪切速率为特征量,分析了剪切应力加载条件、加载量和胶凝体系含水率对含蜡原油乳状液胶凝体系屈服特性的影响规律。引用屈服应变比例系数的概念,分析了不同恒温静置时间后含蜡原油乳状液胶凝体系结构恢复程度及其影响因素。研究发现：屈服应变可作为W/O型含蜡原油乳状液胶凝体系屈服的判据;增大原油乳状液胶凝体系含水体积分数,屈服应变增大,屈服剪切速率减小,体系恢复度增加。增大剪切应力加载量或剪切应力增加速率,原油乳状液胶凝体系屈服剪切速率增大,该体系的结构恢复程度变差。     

双交联型泡沫凝胶的制备及其暂堵压井防漏机理

针对低压储层修井防漏技术难题,研发了一种双交联型泡沫凝胶压井液,基本配方为:3%聚丙烯酰胺+2%起泡剂+1.5%交联剂A+0.1%交联剂B。显微镜观察表明,单一交联型及双交联型泡沫凝胶均具有明显双膜结构,但双交联型泡沫凝胶膜更厚实,气核最外层凝胶膜厚度最大为77.35 μm,气核外层液膜总厚度最大为188.48 μm,表现为较好抗压强度和稳定性,其稳定时间大于10 d,远高于单一交联型体系。流变性与黏弹性测试表明,双交联型泡沫凝胶具有高弹低黏特征,利于泵送和后期返排解堵。暂堵压井模拟实验表明,对于渗透率在90～208 mD的中高渗岩心,在2 MPa正压差下60 min内作用于岩心的压降值≤ 0.05 MPa,滤失量几乎为零,该双交联型泡沫凝胶压井液具有一定抗压能力与低滤失特性,能有效暂堵储层,在低压油气井修井防漏领域具有较好应用前景。      

Rheological and physicochemical characterization of UAE crude oil

This study focuses on the rheological and physiochemical characterization of three samples of light crude oil and fuel oil from the United Arab Emirates. The dependence of density on temperature ranging from 20 to 200°C was determined. Also, the impact of temperature was investigated on viscosity, shear stress τ, shear rate, yield stress, and thixotropic behavior, and characterized by the Haake RheoStress. The exponential decrease of viscosity over temperature range was modeled using Arrhenius equation. The shear stress–viscosity data revealed that crude oil A solely exhibited Newtonian behavior while crude oils B and C and fuel oil followed the Herschel-Bulkley model.