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.     

Interfacial Interactions Between Crude Oil and CO2 Under Reservoir Conditions

Abstract

In this paper, an experimental technique was developed to study the interfacial interactions between crude oil and CO₂ under reservoir conditions. By using the axisymmetric drop shape analysis (ADSA) for the pendant drop case, this new technique makes it possible to measure the interfacial tensions (IFTs) between crude oil and solvents, such as CO₂, at high pressures and elevated temperatures. The major component of this experimental setup is a see-through windowed high-pressure cell. In this study, the IFT of the crude-oil–CO₂ system was measured as a function of pressure at two fixed temperatures. It was found that, due to mutual interfacial interactions between crude oil and CO₂, their dynamic IFT gradually reduces to a constant value, i.e., the equilibrium IFT. The major interfacial interactions observed in this study include light-ends extraction and initial turbulent mixing. At T = 58°C, the equilibrium IFT reaches 1–2 dyne/cm when P ≥ 13.362 MPa, and only partial miscibility is achieved even up to P = 28.310 MPa. Thus, this experimental study shows that only partial miscibility can be obtained in most CO₂ flooding reservoirs. In addition, it is expected that the observed light-ends extraction and initial turbulent mixing phenomena may have significant effects on ultimate oil recovery and long-term CO₂ sequestration.     

Evaluation of interfacial tension between ASP solution and crude oil from B oil field

The interfacial tension (IFT) between alkali-surfactant-polymer (ASP) solution and crude oil is an important parameter for evaluating the feasibility of the ASP flooding for an oil field. The IFT between six series of ASP solution and crude oil from B oil field were measured at 65°C. Each series of ASP solution was composed of NaOH or Na₂CO₃, one of the three kinds of surfactants (S1, S2, and S3), and polymer FT60. The concentration of FT60 and surfactant were 1500 and 2000 mg/L, respectively. The research results show that the IFT between ASP solution and crude oil is ultra-low in the NaOH-FT60-S2 series and NaOH-FT60-S3 series and the best concentration of NaOH is 4000 mg/L and 8000 mg/L, respectively. NaOH-FT60-S2 series is more suitable for B oil field. The IFT between ASP solution and crude oil is ultra-low in the Na₂CO₃-FT60-S2 series and the best concentration of Na₂CO₃ is 4000 mg/L.     

Effect of salinity on the IFT between aqueous surfactant solution and crude oil

The effect of salts and different surfactants on the equilibrium as well as dynamic interfacial tension (DIFT) between crude oil and water was investigated. Three different types of surfactants with identical hydrophobic chain length C₁₂: Sodium Lauryl Ether Sulphate (SLES), Dodecyl Trimethyl Ammonium Bromide (DTAB), Polyoxyethylene (23) lauryl ether (C₁₂E₂₃) were used in this study. SLES shows better synergism of salt and surfactant mixture amongst the surfactants studied. The order of synergism of salts with the surfactant observed was MgCl₂>CaCl₂> NaCl. The results obtained from partition coefficient study show that the addition of salts favours the partition of surfactants into the oil phase hence reduce IFT more effectively. DIFT results reveal that, salt accelerates the surfactant migration towards the interface, hence, reducing the t^* value.     

滨海环境颗粒物对分散溢油表面性质的影响

用室内实验模拟海洋环境的方法,研究了在不同颗粒物浓度和粒径、海水盐度以及pH值条件下,加入不同种类的颗粒物对胜利原油表面性质的影响;同时制备石油 悬浮颗粒物凝聚体(OSAs),并测定凝聚体中油滴平均粒径的大小。结果表明:随着悬浮颗粒物浓度的增加和颗粒物粒径的减小,油 水界面张力和Zeta电位逐渐减小;在加入不同颗粒物条件下油 水界面张力、Zeta电位和油滴粒径均随着海水盐度的增加而减小,加入高岭土时达到最小,分别为02 mN/m、-347 mV和86 μm;油 水界面张力随pH值的增加先减小后增大,Zeta电位随pH值的增加先增大后减小,油 水界面张力最低值和Zeta电位最高值均在pH值为7~8时达到;消油剂和颗粒物共同作用条件下,油 水界面张力、Zeta电位和油滴粒径可分别降低至01 mN/m、-191 mV和19 μm。     

高温高压条件下CO_2-原油-水体系相间作用及其对界面张力的影响

采用轴对称悬滴形状分析技术研究了高温、高压条件下CO_2-原油体系和原油-碳酸水体系的相间作用及其界面张力的变化规律。研究结果表明:在高温、高压条件下CO_2与原油之间的相间作用可分为2个阶段,第1阶段为CO_2溶解并使原油膨胀,第2阶段为CO_2抽提轻质组分并使油相体积减小;压力增大,CO_2与原油的相间作用速度变快,压力接近最小混相压力时,油滴形态变得极不稳定,CO_2对轻质组分的抽提作用增强,CO_2与原油界面变模糊。温度和压力是影响CO_2与原油界面张力的主要因素,温度越高,气液界面越不稳定,动态界面张力波动越大,平衡界面张力越大;压力越高,动态界面张力达到平衡时间越短,最终的平衡界面张力越低。原油-碳酸水体系界面处的相互作用较弱,油水界面清晰,油滴形态稳定。CO_2从水相向油相逐渐扩散过程中,油滴体积不断膨胀并逐渐达到稳定,未出现CO_2抽提轻质组分导致油滴体积减小的现象。随着CO_2在水相中的溶解及向油相中的扩散,界面张力逐渐下降并达到平衡;温度和压力越高,油水界面张力达到平衡的时间越短,油水界面张力越小。     

降压脱气对溶CO2原油乳液中水滴稳定性的影响

通过对CO₂在油/水/乳液中的溶解度、溶CO₂原油的流动性、溶CO₂后油-水间的界面特性、溶CO₂原油乳液的稳定性、油-水界面压力变化的测试与计算,分析溶CO₂原油乳液在降压脱气过程中水滴稳定性的变化规律。结果表明：溶CO2原油乳液中,沥青质等界面活性物质能够迅速地迁移并吸附于油-水界面,并微弱提高油相对CO₂的溶解能力,并使得油-水界面张力快速降低,界面弹性模量增大,降低界面扩张损耗角;溶入CO₂能够降低油相黏度,提高水滴沉降速率,使得原油乳液的分油率增大;降压脱气时,水相中CO₂气泡的析出、长大,迫使水滴膨胀,降低界面上活性物质的浓度,减小了油-水界面压力,使得水滴的聚结稳定性变差,增大了原油乳液的分水率。     

Low IFT gas–oil gravity drainage in fractured carbonate porous media

This paper addresses a study of gas–oil gravity drainage in fractured carbonate rock subjected to gas injection in low interfacial tension. The purpose of the experiments described in the paper was to investigate gas injection in fractured carbonate reservoirs in both secondary and tertiary cases (after water injection), focusing on gravity drainage using equilibrium gas followed by re-pressurization. Gas injection experiments were performed on 20 cm long and low permeable outcrop chalk core surrounded with a fracture established with a novel experimental set-up in reservoir conditions. The core was saturated with binary mixture live oil consisting of C₁ and C₇ of a known composition, while the fracture was filled with sealing material to obtain a homogeneous saturation. After core initialization, the sealing material was removed by increasing the temperature to higher than its melting point and displaced by live oil. Gas was then injected into the fracture and gravity drainage experiments were performed in low interfacial tension (< 0.5 mN/m) where the IFT between the phases were measured experimentally by selecting the proper pressure and temperature.Experiments were performed at different pressures and reversibility of the effect of the interfacial tension was checked by re-pressurization process. The oil recovered from the bottom side of the block was measured versus time.Based on the results of this study, the recovery of oil showed a significant increase by re-pressurization in gravity drainage process. It was also clear that low IFT gravity drainage is capable to recover a significant amount of oil in fractured reservoirs even after water injection.     

Dissociation of polar oil components in low salinity water and its impact on crude oil–brine interfacial interactions and physical properties

Despite many efforts into the study of fluids interaction in low salinity water flooding, they are not probing the basics of transport phenomena between the involved phases. This work is aimed to bring new understanding of fluid–fluid interaction during low salinity water flooding through a series of organized experiments in which a crude oil sample with known properties was kept in contact with different brine solutions of various ionic strengths. Measuring brine pH, conductivity and crude oil viscosity and density for a period of 45 days illustrates the strong effect of the contact time and ionic strength on the dissociation of polar components and physical properties of the crude oil and brine. Besides, the interfacial tension (IFT) measurements show that the interfacial interactions are affected by several competitive interfacial processes. By decreasing the ionic strength of the brine, the solubility of naphthenic acids in the aqueous solution increases, and hence, the conductivity and the pH of the aqueous phase decrease. To verify this important finding, UV–Vis spectroscopy and 1H NMR analysis were also performed on aged brine samples. Notably, there is an ionic strength of brine in which the lowest IFT is observed, while the other physical properties are remained relatively unchanged.     

Oil recovery and CO2 storage in CO2 flooding

In this study, the interfacial tension (IFT) of crude oil-carbon dioxide mixtures was measured to determine the minimum miscibility pressure. CO₂ flooding with sand packs, long cores, and heterogeneous cores was conducted to investigate the oil recovery and storage efficiency. The experiment results show that the interfacial tension decreases linearly with increasing pressure at two different pressure ranges. Under immiscible condition, the oil recovery and storage efficiency are increased by 30.1% and 52.4% when the injection pressure is increased from 13 to 22 MPa, and improved by 16.3% and 22.04% when the permeability is decreased from 270 to 10 mD, respectively. Under miscible condition, increase of injection pressure can only lead to much slower increase of oil recovery and storage efficiency, and permeability almost has no influence on oil recovery and storage efficiency. The oil recovery and storage efficiency can be remarkably reduced by heterogeneity. Water alternating CO₂ injection can improve the oil recovery and storage efficiency by 35.5% and 13.55%, respectively, compared with continuous injection.     

辽河油田超稠油脱水温度优化实验

以辽河油田杜229+84 超稠油区块的油样为实验对象,研究了超稠油的原油密度、粘度、混合原油乳状液密度、粘度、乳状液膜压及混合原油脱水水滴沉降速度等与温度的变化关系;分析了温度对超稠油脱水速度的影响。实验结果表明,温度升高,混合原油及其乳状液的密度、粘度均减小,原油与脱出水密度差先增加后减小,水滴在介质(原油)中沉降速度增加,稠油乳状液膜压降低,升高温度有利于加快超稠油的脱水速度;油水密度差在70~95℃增加幅度最大,原油及其乳状液粘度的减小幅度最大。综合考虑经济因素,超稠油最佳破乳脱水温度为80~95℃。     

A laboratory investigation of carbon dioxide-enhanced oil recovery by focusing on CO2-oil physical properties

Carbon dioxide (CO₂) miscible flooding has become an important method in enhanced oil recovery (EOR) for recovering residual oil. In addition it may help in protection of the environment as (CO₂) is widely viewed as an important agent in global warming. Knowledge of the interactions between (CO₂) and reservoir crude oil is very critical for any (CO₂)-enhanced oil recovery (EOR) projects. This paper shows the effect of (CO₂) miscible flooding application for Egyptian oil fields by swelling studies. The swelling test is a laboratory simulation of the process of injecting gradually different percentage of (CO₂) gas into a reservoir containing under-saturated oil. The gas (injection solvent) can dissolve, causing the reservoir fluid to swell. This paper presents a summary of a wide range of laboratory tests conducted on ten different crude oils varying from 26.4 to 40.5 API. These were used to invested the use of (CO₂) and its effect on parameters such as viscosity, density, gas solubility and swelling factor as a function of pressure at temperature from 620.3 to 706.0?°R.     

Modeling of CO2-brine interfacial tension: Application to enhanced oil recovery

Development of reliable and accurate models to estimate carbon dioxide–brine interfacial tension (IFT) is necessary, since its experimental measurement is time-consuming and requires expensive experimental apparatus as well as complicated interpretation procedure. In the current study, feed forward artificial neural network is used for estimation of CO₂–brine IFT based on data from published literature which consists of a number of carbon dioxide–brine interfacial tension data covering broad ranges of temperature, total salinity, mole fractions of impure components and pressure. Trial-and-error method is utilized to optimize the artificial neural network topology in order to enhance its capability of generalization. The results showed that there is good agreement between experimental values and modeling results. Comparison of the empirical correlations with the proposed model suggests that the current model can predict the CO₂–brine IFT more accurately and robustly.     

Effect of active species in crude oil on the interfacial tension behavior of alkali/synthetic surfactants/crude oil systems

The effect of active species present in crude oil on the interfacial tension （IFT） behavior of alkali/synthetic surfactants/crude oil systems was studied. The system consisted of heavy alkyl benzene sulfonate, sodium chloride, sodium hydrate and Daqing crude oil. Experimental results indicated that active species would diffuse from oil/aqueous interface to aqueous phase and finally an equilibrium could be reached in the system with increasing contact time. Moreover, the minimum IFT and equilibrium IFT values increased with increasing contact time and a linear relationship existed between dynamic IFT and f^-1/2 when IFT value approaching the minimum and after the minimum IFT was reached. This indicated that the dynamic IFT-time behavior was diffusion controlled. The oil and aqueous phases were analyzed by infrared （IR） spectroscopy. IR spectra of oil and aqueous phases illustrated that the content of active species in the oil phase decreased, but the content of active species in the aqueous phase increased after alkali reacted with crude oil. This indicated that the active species present in oil played an important role in reducing IFT.     

Evaluation of Interfacial Tension Between Zahra Oil and ASP Solution

Alkaline-surfactant-polymer (ASP) flooding has been proved to be an effective enhanced oil recovery (EOR) method. Reduction of interfacial tension (IFT) between crude oil and ASP solution is the main mechanism in ASP flooding. Evaluating IFT between crude oil and ASP solution is a key parameter for ASP flooding in laboratory experiments or field projects. In order to obtain good result of ASP flooding in the reservoir in Zahra field, the influence of the concentration of Na₂CO₃ on IFT between Zahra crude oil and ASP solution with three different surfactants, BHJC, SS-231, and SS-233, was researched. IFT was measured with surface tension meter SVT20N, Dataphysics Co. Germany, at 72°C. For the view of IFT result anionic surfactant BHJC is more suitable for the Zahra oil field. This research is helpful for practical application of ASP flooding in Zahra oil field.     

The extraction effect of CO2 injection on the flow properties of crude oil

During CO₂ flooding, extraction of lighter hydrocarbons from crude oil makes the remaining oil hard to be recovered. In this work, we design a new experimental method to characterize the effect of CO₂ extraction on crude oil. The experimental results show that, the volume of extracted hydrocarbons increases as system pressure increases. The hydrocarbons with wider carbon number can be extracted from crude oil at high pressures. Moreover, the wax precipitation and viscosity of the remaining oil increase with increasing pressure. This study is expected to provide the basic understanding of the mechanisms of CO₂ flooding for enhanced oil recovery.     

Compositional modeling and simulation of dimethyl ether (DME)- enhanced waterflood to investigate oil mobility improvement

Dimethyl ether (DME) is a widely used industrial compound, and Shell developed a chemical EOR technique called DME-enhanced waterflood (DEW). DME is applied as a miscible solvent for EOR application to enhance the performance of conventional waterflood. When DME is injected into the reservoir and contacts the oil, the first-contact miscibility process occurs, which leads to oil swelling and viscosity reduction. The reduction in oil density and viscosity improves oil mobility and reduces residual oil saturation, enhancing oil production. A numerical study based on compositional simulation has been developed to describe the phase behavior in the DEW model. An accurate compositional model is imperative because DME has a unique advantage of solubility in both oil and water. For DEW, oil recovery increased by 34% and 12% compared to conventional waterflood and CO₂ flood, respectively. Compositional modeling and simulation of the DEW process indicated the unique solubility effect of DME on EOR performance.     

Effect of polar head surfactants on the demulsification of crude oil

Surfactants can act as demulsifiers to neutralize the stabilizing effect of natural emulsifiers in crude oil. Here, the effect of polar head group of surfactants with identical hydrophobic chain C₁₂ (SLES, SLS, C₁₂E₂₃, BKC, C₁₂E₇) on the demulsification of crude oil emulsion and its effect on water separation rate were studied at different temperature. The activation energy for destabilization was calculated. The results indicate that the rate of water separation increases with temperature and surfactant concentration. The emulsion destabilising activation energy decreases as the concentration of the surfactant increases. The Interfacial Tension (IFT) study showed that when the reduction in IFT was the highest, the water separation rate and efficiency achieved was the highest.     

An Environment-Friendly Alkaline Solution for Enhanced Oil Recovery

Abstract

The injection of alkali and alkali/polymer solutions is a well-known enhanced oil recovery technique. This article demonstrates how wood ash can be used as a source of low cost alkali instead of synthetic alkali that is also environmentally friendly. From the experimental studies, it is found that the pH value of 6% wood ash extracted solution is very close to the pH value of 0.5% synthetic NaOH or of 0.75% Na₂SiO₃ solution. A preliminary microscopic study of oil/oil droplets interaction in natural alkaline solution was carried out in order to understand the oil/water interface changes with time and its effect on oil/oil droplet coalescence. Also, interfacial tension (IFT) was measured for both synthetic and natural alkaline solutions. The IFT values in the presence of acidic crude oil show comparable results.     

微-纳米受限空间原油-天然气最小混相压力预测方法

微-纳米受限空间原油-天然气的最小混相压力(MMP)对致密/页岩油储层注天然气提高采收率参数优化、方案设计及产能预测至关重要,但至今尚缺少获取该参数的可靠方法。针对这一关键问题,提出一种微-纳米受限空间原油-天然气界面张力(IFT)计算方法,通过原油-天然气相平衡计算得到Parachor模型参数从而计算出IFT,并基于界面张力消失法(VIT)预测MMP。该方法改进了气液平衡计算及Peng-Robinson状态方程,考虑了毛细管压力并修正了流体的临界压力和临界温度,简化了传统计算方法,并将气/液相压力考虑到平衡常数K_i的迭代公式中。通过设计8组不同组分天然气并以长庆油田原油和拟注入天然气为实例,分别计算了孔隙半径r_p为5 000 nm、1 000 nm、500 nm、100 nm、10 nm时的IFT和MMP。计算结果表明,压力越高,IFT越小;在r_p为100~5 000 nm时,原油-天然气体系的IFT和MMP基本不受r_p的影响;当r_p≤100 nm时,IFT和MMP显著降低,MMP最大降幅达38.76%,说明致密/页岩油储层注天然气提高采收率相比常规储层注天然气更容易混相。原油-天然气体系的MMP与C₂—C₄含量呈现负相关性,且r_p越小,MMP递减速度越快,最大降幅达57.33%(r_p=10 nm,C₂—C₄摩尔分数增至40%)。将计算结果与文献报道数据进行对比,进一步验证了模型的可靠性。