Change of Yield Stress of Daqing Crude Oil With Thermal and Shear History

Abstract

Daqing crude oil is a typical waxy crude oil with a wax content of 26.6 wt.% and a gel point of 32°C. The yield stress of waxy crude oils is an important property in the process calculation and flow safety analysis for heated oil pipeline. The Daqing crude oil was studied and the yield stress change with shear history was explored through simulation experiment of pipelining. It was found that the change of throughput variation or shear rate showed little effect on yield stress. There existed a peak yield stress on the relation curve of yield stress with final dynamic cooling temperature. The prediction model of yield stress for waxy crude oil under the condition of shutdown was developed and can be used to predict the yield stress of Daqing crude oil at certain heating temperature, final dynamic cooling temperature, and measurement temperature. For the 139 groups of yield stress data of Daqing crude oil from the simulation experiment of pipelining, the result of prediction with this model showed that the average relative deviation between the yield stress measured and predicted is 30.27%, and the coefficient of correlation is 0.9623.     

降凝剂对大庆原油降凝效果评价

筛选出VA含量28％,相对分子质量23000左右的EVA28／03降凝剂,考察了此降凝剂对大庆原油的降凝效果。结果表明,在降凝剂用量100mg／kg,活化温度65℃,热处理时间0．5h,冷却速度0．5℃／min时对大庆原油降凝效果较好,降凝幅度达14．5℃。同时根据降凝剂协同作用的原理,对其与高分子表面活性剂进行了复配实验。结果表明,带有脂肪族碳链及胺类和醚类极性基团的1210、HY1017、1202、Yeyouan1、Yeyouan2对大庆原油都有一定的辅助降凝效果,与EVA28／03（1：1）复配,可使凝点降低15．5℃。     

Prediction of Viscosity Variation for Waxy Crude Oils Beneficiated by Pour Point Depressants During Pipelining

Pour-point-depressant (PPD) beneficiation is an emerging technology for facilitating pipelining of waxy crude oils. However, it was found both in lab studies and field tests that the viscosities of PPD-beneficiated waxy crude oils may increase as a result of pump shear or pipe flow shear during pipelining, called the shear effect. Current method for understanding this viscosity variation is to measure the viscosities by experimental simulation, which is quite time- and effort-consuming for long-distance pipelines. A new method for predicting the viscosity variation during pipelining is presented in this article based on a mathematical model for predicting viscosity of PPD-beneficiated waxy crude oils at certain temperature after shear and a model for predicting non-Newtonian viscosity of waxy crude oils as a function of temperature and precipitated wax. As verification, viscosity variations of five PPD-beneficiated waxy crude oils during pipelining are predicted by using the presented method and compared with the measured data from experimental simulations. The predicted viscosities are in good agreement with the measured data, with an average absolute deviation of 14.1% for all 52 data points. Comparisons between the measured or predicted viscosities during pipelining and viscosities obtained from the fast cooling experiment of PPD effectiveness evaluation demonstrate that the evaluation of PPD effectiveness for practical application should take the shear effect into consideration. The presented method provides a new way to evaluate the PPD's effectiveness in pipelining application quickly and effectively.     

OCS表面活性剂驱油体系与大庆原油间的动态界面张力研究

测定了OCS表面活性剂驱油体系与大庆原油间的动态界面张力.在大庆油田评价浓度范围内,考察了碱的类型与浓度、OCS浓度以及部分水解聚丙烯酰胺(HPAM)对动态界面张力的影响.结果表明,强碱(NaOH)体系比弱碱(Na2CO3)体系更容易形成超低界面张力(10-3mN/m),即体系达到超低界面张力的时问较短;高浓度碱体系比低浓度碱体系更容易形成超低界面张力;弱碱条件下,OCS表面活性剂浓度变化对动态界面张力有一定的影响;而强碱条件下则没有明显的影响;聚合物HPAM的引入使得不同体系达到超低界面张力的时间延长.     

旅大原油降凝剂的研究

针对旅大原油高含蜡特性,比较了本实验优选合成的EVA改性型降凝剂ZLX-01与市售7种降凝剂对旅大原油的降凝效果,并探讨了影响加剂效果的因素。实验结果表明,旅大原油最佳热处理温度为50～55℃,降凝剂ZLX-01最优加剂量为300 mg/L,原油凝点由加剂前的22℃降至9℃,反常点由加剂前的35℃降至30℃。在原油温度25℃、剪速12 1/s下,加入300 mg/L的降凝剂ZLX-01后,原油表观黏度由加剂前的420 mPa.s降至116 mPa.s,降黏率为72.4%。重复加热温度低于40℃时会恶化加剂原油的低温流变性,此外加有ZLX-01的原油还具有较好的静态稳定性。图2表4参2     

大庆原油含氮组分的界面扩张黏弹性质

 采用络合法和吸附色层法对大庆原油含氮组分进行了分离和富集,得到氮含量不同的2种含氮组分（以下简称 N1、N2）。采用悬挂滴方法,研究了 N1、N2在煤油-水界面上的扩张流变性质,考察了扩张频率和组分浓度对扩张模量和相角的影响。结果表明,N1、N2具有相近的相对分子质量,表现出大体类似的界面扩张变化规律;但由于氮含量不同,所以具有不同的界面扩张行为。组分浓度较低时,由于 N1的氮含量较高,其分子结构中含有更多的氮杂环,活性较强,体积较大,表现为油-水界面张力较低,扩张模量较大;组分浓度较高时,由于 N2分子体积较小,在油-水界面上排列更为紧密,易于在界面与体相间发生扩散交换,表现为油-水界面张力较低,扩张模量较小。2种含氮活性组分不同的界面扩张黏弹性质可从其不同特征的微观弛豫过程得到解释。     

降凝剂对高蜡原油流变性的影响

研究了降凝剂对高蜡原油流变性的影响,进行了降凝剂的筛选、不加剂和加剂高蜡原油粘温曲线的测定,考察了重复加热和高速剪切对降凝剂改性效果的影响及降凝剂的静态稳定性。实验结果表明,在70℃温度下,原油中加入100μg/g(EVA AA)降凝剂,原油凝点从35℃降至23℃,并使原油反常点降低,原油的牛顿流体温度范围变宽,非牛顿流体温度下的粘度减小;当重复加热温度低于70℃时,降凝剂的改性效果显著恶化,重复加热温度越低,影响越大;在原油析蜡高峰区,高速剪切将使降凝剂改性效果变差;静态稳定性实验结果表明,该降凝剂静态稳定性较好。     

BEM系列原油流动性改进剂的研制

通过对EVA的醋酸乙烯含量、熔融指数对含蜡原油的降凝影响的研究 ,探讨EVA对含蜡原油的最佳加入量以及不同的结构表面活性剂对原油降凝剂抗重复加热和抗剪切能力的作用 ,BEM降凝平均相对分子质量与含蜡原油蜡碳数分布之间的关系等。研制的BEM降凝剂广泛用于鲁宁线、中洛线等多条管输管道     

稠油磺酸盐及其对稠油的乳化降粘性能研究

乳化降粘开采稠油是一项提高稠油采收率的新技术,开发廉价高效的乳化降粘剂是该技术的关键。以大庆黑帝庙稠油为原料,发烟硫酸为磺化剂,合成了稠油磺酸盐。考察了酸烃比、反应温度、反应时间对磺化反应的影响。确定了磺化反应的最佳工艺条件为：酸烃比1．6：1,反应温度为50℃-55℃,反应时间为2h。测试了其对稠油的乳化降粘性能,结果表明,35℃时,稠油磺酸盐对稠油具有较好的乳化降粘效果,降粘率达90％以上。复配后效果更佳,且具有较好的适用性。     

Effects of Thermal and Shear History on the Viscoelasticity of Daqing Crude Oil

Abstract

The relationship between the viscoelasticity and thermal and shear history of waxy crude is important for the safety analysis of waxy crude pipeline operation. A series of oscillatory shear experiments were performed to test the viscoelastic parameters of Daqing crude oil with a controlled-stress rheometer RSH150. The results indicate that the storage modulus and loss modulus increase in an exponential fashion with decreasing testing temperature. There exists a worst heating temperature for the rheological behavior. The strength of waxy structure and gelation temperature increase as the cooling rate is reduced. The shear action is characterized by energy dissipation due to viscous flow. At the same shear temperature, the strength of waxy structure decreases rapidly and finally attains a stable state as the energy dissipation due to viscous flow is increased. Keeping the same energy dissipation due to viscous flow, the closer the shear temperature is to the test temperature, the lower storage modulus, loss modulus, and gelation temperature would emerge. When being close to or higher than the abnormal point, the shear temperature has few influences on the viscoelasticity. The recovery of waxy structure after shear action exhibits an irreversible property.     

Effects of Thermal and Shear History on the Viscoelasticity of Daqing Crude Oil

The relationship between the viscoelasticity and thermal and shear history of waxy crude is important for the safety analysis of waxy crude pipeline operation. A series of oscillatory shear experiments were performed to test the viscoelastic parameters of Daqing crude oil with a controlled-stress rheometer RSH150. The results indicate that the storage modulus and loss modulus increase in an exponential fashion with decreasing testing temperature. There exists a worst heating temperature for the rheological behavior. The strength of waxy structure and gelation temperature increase as the cooling rate is reduced. The shear action is characterized by energy dissipation due to viscous flow. At the same shear temperature, the strength of waxy structure decreases rapidly and finally attains a stable state as the energy dissipation due to viscous flow is increased. Keeping the same energy dissipation due to viscous flow, the closer the shear temperature is to the test temperature, the lower storage modulus, loss modulus, and gelation temperature would emerge. When being close to or higher than the abnormal point, the shear temperature has few influences on the viscoelasticity. The recovery of waxy structure after shear action exhibits an irreversible property.     

前南高蜡原油降凝剂的研究

文章选择了几种不同的单体进行聚合反应,得到了两种三元聚合物,并分别和EVA进行复配。依次考察了两种复配型降凝剂在不同加剂量和不同温度下对前南原油的降凝效果。实验结果表明:在加剂温度为70℃时,AMS-EVA复配降凝剂的最佳加剂量为0.03%,可使前南原油凝点降低9℃;AVS-EVA复配降凝剂的最佳加剂量为0.1%,可使前南原油凝点降低10℃。这两种复配型降凝剂均可以降低前南原油的黏度,改善其低温流变性。     

高凝原油降凝剂使用效果及性能

对一种新型液体原油降凝剂KYJN-1进行了室内模拟试验,考察了该降凝剂在实际运行环境下的使用性能及存放条件.试验结果表明,在加剂量为50 mg/L,热处理温度为75℃的最佳条件下,该降凝剂能降低原油凝固点8～13℃,现场生产运行环境对降凝效果没有影响,降凝剂现场存放温度为40～45℃.     

A Study on the Interaction of Crude Oil Waxes With Polyacrylate Pour Point Depressants by Monte Carlo Simulation

The interaction of crude oil waxes with polyacrylate pour point depressants (PPDs) bearing different structures was investigated in detail by Monte Carlo simulation, using n-hexadecane as representative component of wax crystal. It was demonstrated that during wax precipitation the mixed energy was low when the side chain length of polyacrylate was close to that of n-hexadecane. Meanwhile, the mixed energy between polyacrylate PPDs and n-hexadecane was shown to be closely related with the polarity of building blocks of polyacrylate. Our results indicated that it is easier for polyacrylate polymers with polar building blocks to interact with n-alkanes, which would effectively inhibit wax-crystal precipitation and improve crude oil low-temperature fluidity. The simulation results provide with some knowledge for guiding the molecular design and synthesis of polyacrylate PPDs.     

水性降凝剂BEM-6N-W的研制

使用固体颗粒状原油降凝剂需要有复杂的溶解、注入装置.将固体颗粒降凝剂BEM-6N在90℃溶于混合溶剂中,配成30%～50%溶液(油相),在60～90℃下其黏度均在103mPa·s数量级.使用用量3%～8%的复配乳化剂及适量杀菌剂,将上述油相乳化在水中,制成15%的水性降凝剂BEM-6N-W.取加量为50 mg/L,对不同剂型的BEM-6N进行了评价.油性降凝剂(1%柴油溶液)、15%水性降凝剂及稀释至1%的水性降凝剂在加剂热处理温度为70℃时,均可使青海原油凝点由28℃降至10℃;在加剂热处理温度为55℃时,只有油性降凝剂对大庆原油有降凝效果,使凝点由35℃降至24℃,当加剂热处理温度提高至60℃时,水性降凝剂对大庆原油也有同样降凝效果.从水性降凝剂在原油中的破乳、分散、溶解出发,解释了以上实验结果.15%水性降凝剂BEM-6N-W于2007年10月在输送青海原油的花格线、2008年10月在输送大庆原油的秦京线试验获得成功.     

A Study on Creep Behavior of Gelled Daqing Crude Oil

Abstract

Gelled waxy crude oils have complex rheological properties. Experimental research and mechanical analogy were performed for the creep behavior of Daqing crude oil. The experienced stages in creep process were partitioned based on the changes of strain and strain rate with the increasing loading time. When the loading stress was lower than the yield stress, there existed three stages; namely, instant elastic deformation, decelerated creep, and constant rate creep. When the applied stress was higher than the yield stress, accelerated creep occurred after the above three stages. By applying mechanical analogy, the elastic element, viscous element, plastic element, and accelerated creep element were employed to reflect the interior strain mechanism of crude oil under creep condition. A creep equation was proposed by incorporation with the analysis on the creep experiment. Based on the creep equation, nonlinear regression was conducted by using the creep experiment data of Daqing crude oil at different temperatures of 28°C, 29°C, 30°C, and 31°C, respectively. The average correlation coefficient was 0.9907. Substituting the calculated equation parameters into the creep equation, the creep behavior under other shear stresses can be predicted at the same temperatures. The average relative deviation is 8.29%. The change of strain of crude oil before yielding can be accurately described by the creep equation.     

大庆原油中界面活性组分研究

用体积比3：7的20g/LNaOH溶液/乙醇液多次萃取酸值0.06mgKOH/g的大庆原油，分离出酸性活性组分，将该组分在色谱柱上用不同溶剂洗脱，得到极性不同的5个级分，其中正已烷级分（6.4%)为烷烃，苯级分（4.7%)为芳烃和稠环烃，丙酮级分（3.5%)和乙酸/乙醇（体积比1：19）级分（8.5%)只含少量脂肪酸，在乙酸乙酯级分（64.0%)中，用气相色谱-质谱方法鉴定出17种正构脂肪酸（C9-C32）和13种异构脂肪酸（C9-C19）并测定了在级分中的含量，测定了原油，萃余油，用正庚烷配制的乙酸乙酯级分模拟油（模拟油1）和C10-C30混合正构烷烃标样模拟油（模拟油2）与不同浓度的的NaOH溶液之间的动态界面张力，模拟油1的界面张力低于模拟油2的界面张力，据此认为异构脂肪酸比正构脂肪酸具有较好的界面活性。     

锦州原油降凝剂的研究

锦州原油为高蜡质原油,本研究针对该原油的特性,优选合成了多种羧酸酯共聚物型降凝剂LF一04,并对试验结果和影响加剂效果的因素进行了分析。锦州原油最佳热处理温度在50℃以上,最优加剂浓度为400mg／L,其原油凝点值由原来的21℃降至9℃,反常点降至40℃,比空白原油反常点降低了5℃。在原油温度25℃,剪速为16s-1下加入400mg／L的降凝剂LF－04,原油表观粘度由原来1150mPa·s降至339mPa·s,降粘率为70．5％。     

含蜡原油加热处理后粘度和析蜡点研究

介绍了一种自动测量粘度与温度曲线的方法。并对含蜡原油加热处理后粘度和析蜡点的变化规律进行了研究。实验结果表明;加热处理后含蜡原油的粘度和析蜡点降低。     

降凝剂对高蜡稠油的改性效果及机理研究

实验研究了工业品原油降凝剂WHP改善含蜡56.9%、其中96.6%为正构烷烃的胜利郑王庄稠油流动性的效果。WHP含乙烯/醋酸乙烯/乙烯醇嵌段聚醚三元共聚物30%-35%。在60℃将WHP加入稠油中,测定其凝点和32℃、0-42.6 s^-1范围5个剪切速率下的黏度,均随WHP加量的增加（50-300 mg/L）而降低,200 mg/L为最佳加量,在该加量下0.32 s^-1黏度由34.16 Pa·s降至79.2 mPa·s,凝点（℃）、屈服值（Pa）、稠度系数（Pa·s^n）分别由49.0、32.42、31.57降至39.5、0.1297、0.02142,流型指数由0.1176升至0.9790。由黏温曲线求出,加入200mg/L WHP使该稠油析蜡点由65℃降至58℃,反常点由70℃降至50℃。根据空白和加剂原油扫描电镜照片显示的蜡晶形态,利用共晶机理分析讨论了WHP这种高分子表面活性剂的降凝、降黏、改善流动性的作用。图3表3参5。