Rheological behavior of Algerian crude oil: effect of temperature and refined product

Abstract

The rheological behavior and its variation with temperature and refined product concentration of a crude oil sample coming from a quagmire of the separation station of Tin Fouye Tabankort oilfield/southern Algeria were investigated experimentally. The experiments were carried out at various temperatures (20, 30 and 50?°C) over the shear rate range of 0 to 700?s^?1 by using a controlled stress rheometer (AR 2000, TA Instrument). The results showed that the crude oil exhibit non-Newtonian of shear thinning behavior at low shear rate and Newtonian behavior at high shear rate and was adequately described by Casson and Herschel–Bulkley models. The rheological measurements through the steady flow test and viscoelastic behavior, including the storage modulus (G′), loss modulus (G″), and complex modulus (G*), has indicated that the rheological properties of the crude oil were greatly influenced by the temperature and the additive concentration.     

Comparative studies of the rheological behavior and microstructural properties of emulsions (oil/distilled water phase) and (oil/Lias water phase)

Abstract

The rheological behavior of crude oil and their emulsions were investigated as a function of two water types (distilled water and the LIAS water). The focus of this work is to obtain more knowledge about the effect of LIAS water concentration, which used to maintain pressure and produced from production of crude oil in the oil fields Tin Fouye Tabankort-south Algeria, on the rheological properties of crude oil. The rheological parameters were measured by using AR-2000 rheometer at 15?°C under dynamic and shear testing conditions. The measured data were first classified into two groups for Newtonian and non-Newtonian fluids. Depends on the type and concentration of water, the non-Newtonian behavior was described in better way by the Casson, Power law and the Herschel–Bulkley models. The results indicated that the viscosity, the yield stress, the elastic modulus, (G′), the loss modulus, (G″), and the microstructure of the prepared emulsions not only varied with water concentration but also by water types.     

Investigating the rheological behavior of Algerian crude oil stemming from station of separation (quagmire)

An experimental study was conducted to investigate the rheological behavior of Algerian crude oil stemming from station of separation (quagmire) of the Tin Fouye Tabankort sector (southern Algeria). The rheological measurements at different temperatures (20°C, 30°C and 50°C) were performed employing AR 2000 rheometer of TA-Instruments. Several parameters such as shear rate, the temperature and the presence of crude oil from another quagmire on the rheological properties have been studied. The experimental results show that the studied crude oil displays non-Newtonian shear thinning behavior at low values of shear rate and a Newtonian behavior at high values of shear rate, which can be best presented by the Casson model. The rheological examination tests (flow and dynamic mode (oscillation)) have shown that the rheological properties of the crude oil were significantly influenced by the temperature and the crude oil addition.     

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.     

Experimental investigation of the yield stress measurements for xanthan solutions and crude oil-xanthan emulsions

Yield stress measurements of xanthan aqueous solutions and crude oil-xanthan emulsions were investigated experimentally. The yield stress study was carried out for wide range of crude oil (0–75% by volume) and xanthan gum (0–10⁴ ppm) concentrations. Two types of xanthan polymers of Sigma and Kelzan were used for the current study. Aqueous solutions with higher xanthan concentration displayed higher cycles of shear rate-shear stress rheograms. Both aqueous solutions of Sigma and Kelzan showed similar behavior for concentration of ≤1000 ppm, however, Sigma solutions of higher concentrations reported slightly higher flow behavior than Kelzan. Similar rheogram behaviors are found for both Sigma and Kelzan emulsions up to concentration of 5,000 ppm. However, for 10,000 ppm, a slight higher profile for Sigma emulsions was reported.     

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.     

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.     

Rheology of Doped Nigerian Niger-Delta Waxy Crude Oil

Abstract

Precipitation and deposition of wax, which usually results from temperature lowering, has detrimental effects on petroleum industry operations. To appreciate and understand the physicochemical mechanics of wax precipitation, rheological experiments were carried out on three doped and undoped Nigerian waxy crude oils. The characteristic shear stress straining rate shows an initial constant shear stress below 50 sec^?1 shear rate, followed by a gradual increase above 50 sec^?1 which is indicative of energy consumption in the partial break-up of wax matrix bonds. Doping greatly ameliorates the rheological properties and pour points of the crude oils. The Bingham plastic model excellently fit the experimental data, with a correlation coefficient ≥ 0.97721.     

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.     

Shear strengthening viscosity and shear-rate-dependent modulus model for a Shengli crude oil

The steady shear viscosity of a Shengli waxy crude oil at the temperature of 3°C to 4°C, higher than its gel point, was measured by using a parallel-plate rheometer, which shows a shear thickening behavior in the shear rate range of 10^?2–10^?1 s^?1. A spectrum model proposed in our previous work was modified here by considering the modulus change in the spectra, which could be caused by a shear-induced varying internal structure in the crude oil. The shear strengthening viscosity of the Shengli crude oil can be described well by the changing-spectrum viscosity model.     

疏水缔合聚合物溶液粘弹性及流变性研究

实验测定了缔合聚合物溶液的动态粘弹性、流变性以及在多孔介质中的流变特性.动态粘弹性实验结果表明,在聚合物溶液浓度大于临界缔合浓度时,溶液的弹性模数G'和耗能模数G″明显大于聚合物溶液浓度低于临界缔合浓度时的G'和G″,且存在着一个临界聚合物浓度.低于该浓度时,溶液的G″大于G',而高于该浓度时, G'大于G″,不同浓度下的G″和G'基本不受剪切应力的影响.在实验剪切速率内,缔合聚合物溶液的宏观流变特征表现为剪切稀释性和剪切增稠性.而在多孔介质中,在低剪切速率下,溶液表现出牛顿流体的特征;随着剪切速率的增加,溶液表现出剪切稀释性和剪切增稠性的流变规律.在进行缔合聚合物驱油时,应尽可能使用弹性比较大的聚合物,而且注入速度须高于临界粘弹流速,这样才能充分利用其粘弹性提高采收率.     

CFD investigation on characteristics of heavy crude oil flow through a horizontal pipe

Transportation of heavy crude oil via pipelines possesses many technological issues that are inherently flow related. Accurate prediction of flow characteristics is an essential step for a reliable piping design of transporting the crude oil. A rheology-based Computational Fluid Dynamics (CFD) model of the Iraqi heavy crude oil flow through a horizontal pipe (1 m length of 3/4 in. inside diameter) was developed using the commercial software Ansys 15 Fluent. By using power law rheological model, the Iraqi heavy crude oil exhibits a non-Newtonian dilatant behavior over the examined shear rate range of 1–40 s⁻¹. The proposed axi-symmetric CFD model identifies velocity profile and generates values of friction factor, which are validated with experimental measurements. Additionally, wall shear stress and entrance length were numerically predicted and compared with well-established correlations from the literature for Non-Newtonian flow. Detailed results of the CFD model exhibited a reliable prediction of the characteristics of heavy crude oil flow.     

An empirical correlation for estimating the viscosity of non-Newtonian waxy crude oils

Non-Newtonian fluids are the most complex ones when it comes to predicting their flow behavior. In the pre-existing models, rheological behavior in waxy crude oils is mainly affected by shear rate and thermal history of crude oils. In the present work, rheological characteristics of four different crude oils were studied by coaxial cylindrical rheometer at three different temperatures (40°C, 50°C, and 60°C) and a model was proposed keeping into consideration wax content for the first time. This model is prepared to predict the viscosity of four different crude oils with different wax content and at different temperature. The proposed model can efficiently estimate the viscosity as compared to other established models.     

多分量地震全波形弹性反演预测砂岩油藏剩余油分布

中国东部油田经过几十年的开采,主力油层先后进入高含水后期,但仍有相当一部分原油留存在地下。笔者依据中国东部油田原油及地层水的物性特征,分析并研究了流体黏滞性对饱和岩石剪切模量的影响以及黏滞流体剪切模量的变化规律,提出了基于Krief模型和广义Gassmann方程的剪切模量分解及油、水识别方法,并在此基础上进行油水分布预测。根据地震波场的矢量特性和东部油区陆相沉积地层特征,将全波形弹性波动方程反演方法应用于叠前多分量数据处理,获取深度域地层密度、拉梅常数和剪切模量。在大庆油田某油区2D3C地震数据的应用结果表明,利用多分量地震数据全波形弹性反演和流体剪切模量可以比较好地识别油和水,预测剩余油分布。     

Rheological behaviour of crude oil: Effect of temperature and seawater

The effect of temperature and seawater on rheological behavior was investigated in this work for four samples of crude oil from Algerian Sahara. The Newtonian model was used to fit the shear stress dependence on the shear rate for temperature range between 20 and 100°C. The temperature increase leads to a decrease in the dynamic viscosity of crude oil. The temperature dependence of dynamic viscosity was fitted by the Walther equation. For crude oil emulsion, the Herschel-Bulkley model was used to fit the shear stress dependence on the shear rate for volume fraction of seawater between 30 and 70%. The increase in the volume fraction of seawater induces not only an increase in the yield stress and the consistency index of crude oil emulsions but also a decrease in the flow index of crude oil emulsions.     

An Experimental Study of Rheological Properties of Nigerian Waxy Crude Oil

Abstract

Nigerian crude oils are known for their good quality (low sulfur, high American Petroleum Institute gravity). However, similar to any other paraffinic-based crudes, most Nigerian crudes contain moderate to high contents of paraffinic waxes. These waxy crudes exhibit non-Newtonian flow behavior at temperatures below the cloud point because of wax crystallization. In order to accurately predict flowing and static temperature profiles, design waxy crude oil pipelines, evaluate flow interruption scenarios, and start up requirements in the handling of waxy crude oils, the effect of temperature and shear rate on the rheology of crude oils must be determined. This work presented some experimental results on the rheology of two waxy crude oils produced from different Nigerian oil fields. A Brookfield DV-III ultraprogrammable rheometer (Brookfield Engineering Laboratories, Middleboro, MA) was utilized. The temperature dependence of rheological properties and thixotropy of these crudes were investigated. The influence of some petroleum-based diluents to depress the wax appearance temperature (WAT), their effect on the thixotropic/yield pseudoplastic behavior of two Nigerian crudes were studied and it was observed that lower wax content crude has higher tendency to regain its cohesive lattice bonding (yield strength) when left undisturbed for some days at its gel point after agitation. The experimental results showed that the addition of petroleum-based diluents to the lower wax content crude oil leads to its lost some of its yield strength regaining capacity.     

A new experimental investigation on upgrading of waxy crude oils by methacrylate polymers

Several methods have been used to reduce problems caused by wax precipitation during the production and/or transportation of waxy crude oil. Polymers are used to improve pour point and rheological behavior of waxy crude oils. In this work, the influence of the polymer inhibitors such as methacrylate polymers, as wax inhibitor, with different range of molecular weight and alkyl side chain carbons on the rheological behavior and pour point of two Iranian waxy crude oils were evaluated. Two Iranian waxy crude oils were selected on the basis of wax and asphaltene contents. The rheological behavior of these crude oils in absence and in presence of methacrylate polymer was studied. The rheological data cover the temperature range of–1 to 12°C. The results indicated that the performance of methacrylate polymer was dependent on the molecular weight, alkyl side chain carbons and the asphaltene content of crude oil. Methacrylate polymers with longer alkyl side chains than 18 carbons would perform best as wax inhibitors in two cases. Also, for crude oil with low asphaltene, higher molecular weight methacrylate polymer is the best flow improver and lower molecular weight methacrylate polymer showed good efficiency for crude oil with high asphaltene content.     

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.     

利用能量耗散率计算管流的平均剪切率

含蜡原油的流变性与其所经历的剪切历史有关.以往用截面平均剪切率或湍流时的管壁剪切率衡量流体管流的剪切历史,有不当之处.根据能量耗散率与剪切率的关系,提出了按流体的体积平均能量耗散率计算流体平均剪切率的方法,即可根据流体的密度、平均流速、管道直径、流动的摩擦因子或摩阻压降以及流变参数计算牛顿流体和幂律流体管流的平均剪切率.对于湍流,按本方法计算的平均剪切率能合理地度量流体的平均剪切历史.在原油管道正常运行的雷诺数范围内,按截面平均方法计算的湍流剪切率比按体积平均能量耗散率计算的结果约偏低20%～40%.     

Comparative Studies on Synthetic and Naturally Extracted Surfactant for Improving Rheology of Heavy Crude Oil

Effect of surfactants on rheological properties of heavy crude oil obtained from Mehsana Asset, Gujarat, India, were studied. Studies on effectiveness towards flow behavior were made using a surfactant extracted from a tropical Indian plant Madhuca longifolia (Mahua) and nonionic surfactant Brij-30 considering various contributing parameters such as temperature, concentration, and shear rate. Tests were performed at controlled shear rate. At 25°C, 2000 ppm Mahua and Brij-30 addition reduced viscosity of crude oil by 48% and 52%, respectively. Complex and viscous modulus of crude oil decreased significantly due to addition of both the surfactants. FTIR studies of crude-surfactant mixture showed remarkable decrease in concentration of viscosity enhancing groups such as alkanes, alcoholic, and acidic groups indicating the effectiveness of both the surfactants. Naturally extracted surfactant may be used as flow improver for transporting heavy crude oil.