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.     

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.     

Rate of hydrate formation in crude oil/gas/water emulsions with different water cuts

The formation of gas hydrates in gas and oil subsea pipelines can result in blockages and shutdowns. Understanding of the formation process and its kinetics will be helpful for predictions of the amount of hydrates expected to form under defined conditions. In the present work, mixed gas hydrates of methane, ethane and propane are formed in crude oil emulsions with different water cuts in a stirred constant volume high pressure cell. The rate of hydrate formation for each crude oil is evaluated at different stirring rates. The stability of the emulsion made by each crude oil is also tested at different water cuts and stirring rates. At 80% water cut, hydrate growth occurs in two steps. The first step displays slow growth. The transition between the steps corresponds with inversion of the emulsion. Regarding the stability of emulsion, more stable emulsions are correlated to higher rates of hydrate formation. The rate of hydrate formation at 50% water cut was higher than at 80% water cut independent of oil composition and stirring rate.     

稠油乳状液的流变性试验研究

用四种不同的粘性原油乳状液进行了乳状液流变性的研究。结果表明，剪切应力与剪切速率的关系和液滴尺寸大小密切相关，视粘度和非牛顿性随液滴尺寸减小而增大。大部分乳状液在低剪切速率下（＜５０Ｓ－１）剪切变稀，当剪切速率超过５００ｓ－１时呈现牛顿流体性质。因此．液滴尺寸是乳状液流变性研究中的重要因素。     

非牛顿原油渗流流变特性及其在油田开发中的应用

根据实验结果，归纳出了我国非牛顿原油非线性渗流的类型主要有3种。讨论了非牛顿原油单相渗流特征及其渗流渗透率与启动压力梯度的关系，研究了非牛顿拟塑性原油油水两相渗流特征及水驱开采特征。并介铝了非牛顿原油渗流流变特性在油田开发中的应用实例。     

Thermophysical interface properties of crude oil and aqueous solution containing sulfate anions: experimental and modeling approaches

Abstract

Sulfate anion is well-known for being one of the most active agents to be injected into the oil reservoirs and being capable of not only altering the interfacial properties of crude oil but also enhancing the water solution properties in oil recovery. In the current study, the effects of temperature and pressure were studied on interfacial tension (IFT) as well as the adsorption behavior of two different solutions containing sulfate anion using experimental measurements and modeling approaches. Although it was expected that IFT values of the studied systems might decrease as temperature increased due to the improvement in the molecule mobility and solubility of crude oil in water, which consequently might lead to the reduction in its free energy, the reverse trend was observed. The measured dynamic IFT values and adsorption behavior revealed that surface excess concentration of natural surfactants (Г_NS) can be considered as the most effective parameter on interpreting IFT behavior as a function of temperature.     

On the rheology of oil (Review)

Current ideas concerning oil rheology, in particular, that of heavy oils and water–oil emulsions have been considered. It has been shown that petroleum in general is a viscoplastic medium, whose rheological properties in many cases are satisfactorily described in terms of the simple Bingham model. Typical characterization of rheological properties reduces to measurement of the yield point and the pour point and to conditional values obtained by measuring viscosity in viscometers of various types. However, both the yield stress and plastic viscosity are structurally sensitive, resulting in dependence of the rheological properties of oil on the temperature and deformation history, including the kinetics of cooling, which is characterized by a hysteresis curve in the measurement of viscosity. The kinetics of change in the rheological properties of oil depends on the concentration of crystallizable paraffins and other components. Rheology is modified largely by introducing pour point depressants into the oil. Another method for controlling the rheological properties of oil is to convert it into the state of water–oil emulsion using various surfactants. The general formulation of the problem of pipeline oil transport has been discussed, involving calculation based on the knowledge of both the rheological properties of oil and the kinetics of transient structuring processes. The latter is especially important for start-up modes of pipeline operation.     

Improvement of rheological properties of Algeria crude oil by addition of extra-light crude oil and a surfactant agent

Abstract

Effect of surfactant and extra-light crude oil addition on the rheological behaviors of an Algeria crude oil in order to improving its flowability were studied at low temperature. These rheological properties include steady flow behavior, yield stress and viscoelastic behavior. An AR-2000 rheometer was employed in all of the rheological examination tests. Results show that Toluene and extra-light crude oil addition causes a strong reduction in viscosity, the yield stress and can effectively increase of crude oil transport capacity. The toluene addition gets its best flow capacity and lowest viscosity at 6%. The extra-light crude oil addition obtains its best flow capacity and lowest viscosity at 50%. The viscoelasticity character of the crude oil has indicate a significantly influence by the addition of Toluene and extra-light crude oil.     

Influence of polymers on the stability of Gudao crude oil emulsions

The influence of different types and concentrations of polymers on the stability of Gudao crude oil emulsion was investigated by measuring the volume of water separated from the emulsions and the interfacial shear viscosity of the oil/water interfacial film. Experimental results indicate that the simulated water-in-oil emulsion with 40 mg/L of partially hydrolyzed polyacrylamide （HPAM） 3530S could be easily broken by adding demulsifier C and was readily separated into two layers. However, HPAM AX-74H and hydrophobically associating water-soluble polymer （HAP） could stabilize the crude oil emulsion. With increasing concentration of AX-74H and HAP, crude oil emulsions became more stable. Water droplets were loosely packed in the water-in model oil emulsion containing HPAM 3530S, but water droplets were smaller and more closely packed in the emulsion containing AX-74H or HAP. The polymers could be adsorbed on the oil/water interface, thereby increasing the strength of the interracial film and enhancing the emulsion stability.     

Demulsification of Asphaltene-Stabilized Emulsions—Correlations of Demulsifier Performance with Crude Oil Composition

Model asphaltene-stabilized emulsions are used to study the impact of oil composition on the efficiency of demulsification. Varying ratios of toluene and heptane, mixed with asphaltene extracted from a Gulf of Mexico crude oil, were mixed with water to produce emulsions that exhibited characteristic coalescence (water drop) rates. Commercial demulsifiers of varying types and chemistries were added to these emulsions, and resultant rates of water drop measured and compared. Emulsion stability and demulsifier effectiveness are shown to be highly dependent on overall aromaticity of the crude as measured by hydrogen-to-carbon molar ratio. Correlations of observed behavior with actual crude emulsions and demulsifier performance were observed and are reported.     

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.     

Experimental investigation of the effects of various parameters on viscosity reduction of heavy crude by oil–water emulsion

The effects of water content, shear rate, temperature, and solid particle concentration on viscosity reduction(VR) caused by forming stable emulsions were investigated using Omani heavy crude oil. The viscosity of the crude oil was initially measured with respect to shear rates at different temperatures from 20 to 70 C. The crude oil exhibited a shear thinning behavior at all the temperatures. The strongest shear thinning was observed at 20 C. A non-ionic water soluble surfactant(Triton X-100) was used to form and stabilize crude oil emulsions. The emulsification process has significantly reduced the crude oil viscosity. The degree of VR was found to increase with an increase in water content and reach its maximum value at 50 % water content.The phase inversion from oil-in-water emulsion to water-inoil emulsion occurred at 30 % water content. The results indicated that the VR was inversely proportional to temperature and concentration of silica nanoparticles. For water-in-oil emulsions, VR increased with shear rate and eventually reached a plateau at a shear rate of around350 s-1. This was attributed to the thinning behavior of the continuous phase. The VR of oil-in-water emulsions remained almost constant as the shear rate increased due to the Newtonian behavior of water, the continuous phase.     

Optimization of chemical demulsifications of water in crude oil emulsions

The instability of the water in crude oil emulsion and separation of the dispersed water as free water are influenced by the emulsion properties and the operating parameters during the demulsification process. This study aims to relate these properties/operating parameters to the amount of separated water. Steps were taken to determine and validate the optimal separations that can be achieved. Six operating parameters were identified through sensitivity analyses to have an energetic effect on percentage water separation. The bottle test method was used on two different samples of water in oil synthetic emulsions (sample A and B from different Nigerian oil fields). Response surface methodology central composite design (RSMCCD) was used to design the experiment, and generate the desired regression equations/models. Results show that optimum percentage water separations of 93 and 95% (V/V) were achieved with the emulsions A and B respectively using the combination of the optimal variables derived from the model equations. These were improvements from percentage water separations of 80 and 83% (V/V) achieved using the two crude oil samples in their naturally occurring state when the properties of the emulsions were not enhanced to their determined optimal operating conditions.     

Experimental investigation of the rheological behavior of algerian crude oils from the quagmires

In this work, the rheological behavior for three types of crude oil coming from different quagmires namely Amassak, Tamendjelt and Tin Fouye of the TFT sector (Tin Fouye Tabankort/South Algeria) has been experimentally investigated. A controlled stress rheometer (AR 2000, TA Instrument) was used throughout this investigation. The experimental measurements in terms of flow and dynamic tests were carried out at different temperatures during the shear rate over the range of 0–700?s^?1 and frequency range of 0.1–10?rad/s. The obtained results show that the viscosity and shear stress of the crude oils decreases about 53.30%, 58.80%, and 59% respectively, when the temperature increased from 10 to 20?°C. The yield stress required to flow of crude oils also decreased to 37.06%, 89.78%, and 77.53% respectively. The dynamic analysis of the crude oils by identifying of the storage modulus (G′) and the loss modulus (G″) has indicated that the rheological properties of crude oils were significantly temperature-dependent.     

Flow characteristics of xanthan solutions and their crude oil emulsions in terms of thixotropic behavior

The thixotropic characteristics of xanthan solutions and their emulsions with crude oil were investigated experimentally. Understanding these characteristics are required for the crude oil displacement mechanism by polymer solution during the enhanced oil recovery phase. RS100 rheometer with a cone and plate device was employed for this examination using controlled-rate mode. Two crude oil concentrations of 25% and 75% by volume were examined. A wide range of xanthan gum concentration of 500–10⁴ ppm was covered. This study results that the aqueous solutions of xanthan gums showed thixotropic behavior. The high concentrations of xanthan solutions provide higher hysteresis loop than the solutions of lower concentrations. The existence of crude oil within the xanthan emulsions considerably elevates the thixotropic rheograms profile.     

Determination of water content in crude oil emulsion by LF-NMR CPMG sequence

Transverse relaxation times (T2) and T2 spectrum for crude oil emulsions with different water content are obtained by low field nuclear magnetic resonance Carr-Purcell-Meiboom-Gill sequence and various methods to determine the water content are investigated. The results show that there are three methods to accurately determine the water content. When water content is greater than 20.0wt%, determination through T2 value of emulsions is fastest with the relative error below 2.5%. T2 spectrum show the characteristics of multiple peaks, and T2 value of the peaks originated from water are suitable for determination of water content for O/W emulsions. A method is developed and optimized to determine the water content by using the peak-area ratio in T2 spectrum, which is not limited by the water content and the form of emulsion.     

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.     

Experimental investigation of interfacial tension and oil swelling for asphaltenic crude oil/carbonated water system

The phenomenon of oil swelling at the oil-carbonated water (CW) system could be an important mechanism during the water alternating gas (WAG) injection process. Nevertheless, the study of the main mechanisms during water flooding (WF) is a complex topic that has not been well revealed so far, especially for asphaltenic crude oil (ACO) systems. Hence, the main goal of this experimental work is to determine the influence of carbon dioxide (CO₂) within the water phase in the interfacial tension (IFT) between water and crude oil for an extensive range of pressures between 400 psi and 2000 psi (i.e. 2.76–13.79 MPa), under two temperatures of 313.15 and 323.15 K (i.e. 40 and 50 °C) by axisymmetric drop shape analysis (ADSA) method. The experimental results demonstrate that the water/ CW and crude oil IFTs decline with time. The value of dynamic IFT (DIFT) between CW and crude oil decreased about 6 mN/m in comparison with the oil–water DIFT. As a result of the CO₂ solubility, the crude oil droplet swells with increasing pressure. When the temperature rises, the effects of increasing entropy phenomena and decline of liquids density is dominant compared to the solubility of CO₂. Thus, the volume of oil droplet increases with temperature, unexpectedly. In addition, as thetemperature increases the water/CW-Oil IFT is slightly reduced over a wide range of pressure evaluated. Nevertheless, there is a slight increase as the pressure increases for the water–oil system. According to the predicted results, interfacial tension of the CW-oil system declines with increasing pressure until the solubility of CO₂ is reached to a maximum value and then approximately remains changeless.     

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.     

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%。