声波振动与岩石表面润湿性

通过水与岩石表面接触角的测定、声被驱油实验和理论分析,研究考察了声波振动对原油─岩石、水─岩石界面特性的影响,从界面化学角度对岩石表面的润湿性和声波驱油机理进行了探索。结果表明:经原油浸泡后,由于原油中极性化合物(胶质、沥青质等)在岩石表面的吸附,岩石表面由水相润湿为主转变为油相润湿为主;无论岩石表面以水相润湿为主还是油相润湿为主,在水浸泡过程中,声波振动可促进其表面亲油性减弱和亲水性增强,毛细管阻力降低;伴随着岩石表面润湿性的改变,原油对岩石表面的粘附功明显降低;减弱了原油与岩石表面间的粘滞力,使原油更易于从岩石表面上剥离,提高原油采收率;岩石的渗透率越低,声波振动作用越显着。     

特低渗砂岩油藏CO2-低界面张力黏弹流体协同驱油机理研究

目的特低渗油藏储层物性差、层间非均质性强,造成CO₂驱易发生气窜,提高采收率效果欠佳,其中,CO₂水气交替驱作为结合CO₂驱和水驱优势的方法,具有较高的适用性。为进一步改善CO₂-水交替驱的开发效果,开展了CO₂-低界面张力黏弹流体协同驱油研究。 方法通过界面张力和润湿性能测试评价低界面张力黏弹流体基本性能,并利用微观可视化驱油实验及岩心驱油实验等,探究了不同驱替方式的驱油效果和CO₂-低界面张力黏弹流体协同驱油过程中二者之间的“协同作用”机理。 结果低界面张力黏弹流体具备良好的界面活性和改变岩石表面润湿性能力,水驱后开展CO₂驱、低界面张力黏弹流体驱、CO₂-低界面张力黏弹流体交替协同驱,采收率可在水驱基础上分别提高0.91%、10.66%、16.25%,其提高采收率机理包括降低界面张力、改善流度比、改变岩石表面润湿性及乳化作用的协同效应等。 结论CO₂-低界面张力黏弹流体协同驱既可有效增强非均质特低渗砂岩油藏注CO₂过程中气体流动性控制,又能够降低CO₂萃取轻烃导致重质组分沉积的影响,具有协同增效作用。      

A novel test method for evaluate asphaltene inhibitor efficiency on reservoir rock

Asphaltene deposits can reduce the productivity of the reservoir as well as foul piping and surface equipment. Current chemical and mechanical methods for treating deposition are only partially effective partly because the deposition process is poorly understood. The most commonly way to asphaltene precipitation reduction is applying an asphaltene inhibitor. In order to investigate the extent of formation damage by asphaltenes in crude oil this work has used electro kinetic technique to study the adsorption of asphaltenes in rock pores. Most researchers investigate the kinetics of adsorption by monitoring changes in the concentration of asphaltene or polymer in a dispersion of adsorbent particles or capillaries. This study is a coherent approach to measure amount of asphaltene adsorption on rock surface and survey effect of asphaltene inhibitors on precipitation reduction in porous media.     

辽河原油沥青质及胶质油水界面化学性质初探

对由辽河原油中分别提取的沥青质组分,胶质组分配成的模型油与水的界面性质进行了研究,还考察了油相芳香度对涸青质,胶质模型油油水界面粘度的影响及当模型油中沥青质与胶质共存时的油水界面性质。结果表明,含沥青质的模型油的油水界面粘度较高,界面老化现象严重;而仅含胶质的模型油的油水界粘度较小。     

CO2 miscible flooding in low permeability sandstone reservoirs and its influence on crude oil properties

Miscible CO₂ injection process has become widely used technique for the enhanced oil recovery in low permeability reservoirs. Core flooding experiments and field test of CO₂ miscible flooding in low permeability sandstone reservoirs and its influence on crude oil properties was studied. The results showed that CO₂ miscible flooding in low permeability sandstone reservoirs can enhance oil recovery both in laboratory study and field test. The permeability of sandstone reservoirs decreased during CO₂ miscible flooding due to the precipitation of asphaltene of crude oil. The precipitation of asphaltene lead to a reduction of asphaltene content and the apparent viscosity of crude oil. A further study on inhibitors and removers for asphaltene deposits from crude oil should be investigated to prevent and remove asphaltene deposits in low permeability sandstone reservoirs.     

CO2驱油过程中孔喉结构对储层岩石物性变化的影响

注CO₂提高储层原油采收率过程中,储层中流体的渗流和分布受岩石孔喉结构控制,且注入的CO₂会引发原油中的沥青质沉淀,导致储层渗透率下降并改变储层的润湿性。通过在4块渗透率相似但孔喉结构不同的岩心上进行的混相和非混相的CO₂驱油实验研究了CO₂驱油过程中岩石孔喉结构对储层岩石物性变化的影响。基于岩石孔径分布和压汞曲线,根据分形理论对岩心孔喉结构特征进行定量评估。实验结果表明,在提高原油采收率方面,混相驱替比非混相驱替高12.2%~16.8%,孔喉结构相对均质的岩心比非均质岩心高18.1%~26.9%,在非混驱替时原油采收率受岩心孔隙结构的影响更明显。由于沥青质沉淀堵塞孔喉,混相和非混相驱替后岩心渗透率分别下降了7.5%~14.2%、4.0%~7.9%,且渗透率下降幅度与岩心孔喉结构分形维数呈正比。混相和非混相驱替后岩心的润湿指数分别下降了26.8%~59.8 ％、10.5%~21.6%。由于更大的CO₂波及体积,孔喉结构相对均质的岩心水湿性减弱更显著。混相驱替和均质的孔喉结构使岩心物性变化分布更均匀,且均质的孔喉结构可以在提高CO₂驱油效率的同时,减弱沥青质沉淀造成的岩心渗透率下降及润湿性变化,减弱程度分别为3.5%~6.7%、11.2%~33.0%。     

The Effects of Asphaltene Deposition on Unconsolidated Porous Media Properties during Miscible Natural Gas Flooding

The deposition of asphaltenes in porous media is a complex phenomenon, which needs to be investigated under dynamic flowing conditions. Here, the likelihood of asphaltene deposition problems during dynamic displacement of dead oil by natural gas in unconsolidated porous media is experimentally inspected. Dynamic experiments showed a considerable increase in asphaltene deposition in the unconsolidated matrix during natural gas injection. The results show that increase in asphaltene deposition leads to pore plugging, porosity, and absolute permeability reduction of the porous media. Irreducible water measurements show that natural gas-induced asphaltenes change the sandstone wettability to oil-wet.     

Effect of dispersants on the kinetics of asphaltene settling using turbidity measurement method

Organic deposition especially asphaltenes in reservoirs, wells, and equipment has a detrimental effect on petroleum economy. Generally, for chemically control of asphaltene precipitation using dispersants and inhibitors of precipitation or solvents of asphaltene is very common. Although asphaltene in crude oil is stable under specific conditions, but there is no assurance that the system will be stable and asphaltenes could be remaining in suspension state. In this study, the kinetic effects of three dispersants on stabilization of asphaltene aggregates were investigated by turbidity measurement method. Turbidity measurement showed as the dispersant strength rises, the turbidity of unstable sample containing dispersant less declines versus time. In order to carry out further studies on dispersants, the effect of dispersant on asphaltene particle size distribution was investigated. The results of asphaltene particle size distribution measurements showed that adding dispersant cause to decrease the volume percent of particles with medium diameter.     

The Effects of Asphaltene Deposition on Unconsolidated Porous Media Properties during Miscible Natural Gas Flooding

Abstract

The deposition of asphaltenes in porous media is a complex phenomenon, which needs to be investigated under dynamic flowing conditions. Here, the likelihood of asphaltene deposition problems during dynamic displacement of dead oil by natural gas in unconsolidated porous media is experimentally inspected. Dynamic experiments showed a considerable increase in asphaltene deposition in the unconsolidated matrix during natural gas injection. The results show that increase in asphaltene deposition leads to pore plugging, porosity, and absolute permeability reduction of the porous media. Irreducible water measurements show that natural gas-induced asphaltenes change the sandstone wettability to oil-wet.     

AGGREGATION OF ASPHALTENES OBTAINED FROM A BRAZILIAN CRUDE OIL IN AROMATIC SOLVENTS

Surface and interfacial tensions in model systems formed by a Brazilian crude oil n-pentane insolubles (C5I) and n-heptane insolubles (C7I) in three different aromatic solvents: toluene, pyridine and nitrobenzene, were measured at room temperature, employing an automatic tensiometer and using the ring method. The results obtained indicated possible asphaltene aggregation and allowed the determination of critical micelle concentrations (c.m.c) for both C5I and C7I fractions in each of the three solvents considered. In toluene and pyridine solutions, the C5I fraction consistently presented higher c.m.c. values indicating a lower tendency of association for the organic fraction contained in the C5I, and absent in the C7I. In nitrobenzene solutions, this extra organic fraction appears to facilitate asphaltene association, possibly due to the formation of mixed aggregates. Average molecular areas for asphaltenes adsorbed at different interfaces were estimated using measured tensions and found to be in agreement with literature values and suggest a the flatwise surface adsorption of asphaltene molecules. This is consistent with the currently accepted stacking aggregation mechanism of asphaltenes.     

原油沥青质在油藏岩石表面的吸附特性

选用两种原油沥青质样品，对沥青质在岩石孔隙表面的吸附及吸附所引起的润湿性变化进行了实验研究。对润湿性的测定结果表明，油藏岩石润湿性改变的程度主要取决于沥青质的来源和地层水的离子组成，同时也与离子浓度和岩样的束缚水饱和度有关。通过使用分光光度法测定沥青质在砂岩上的吸附量，初步建立了润湿指数（ＷＲ）与沥青质吸附量（ａ）之间的定量关系。对于某一给定的原油沥青质，ＷＲ值随ａ值增加而趋于降低。图４表３参１０（邓春萍摘     

蒸汽驱对储层润湿性的影响

储层润湿性决定着注入流体在储层中渗流的难易程度,对原油的驱油效率、采出程度起着决定性作用。为了明确蒸汽驱过程中储层润湿性的变化,通过室内实验非稳态法水驱油、蒸汽驱油测定油藏相对渗透率曲线的变化,研究了疏松砂岩油藏蒸汽驱对储层润湿性改变的影响。实验结果表明,由水驱到蒸汽驱,油相相对渗透率增加,残余油饱和度下降,残余油饱和度对应的水相相对渗透率增加,等渗点右移;综合相对渗透率曲线特征表明,蒸汽驱使得储层润湿性向亲水方向发展。通过非稳态法研究相对渗透率曲线,由相对渗透率曲线特征点的变化来判断储层润湿性的改变简单易行,蒸汽驱对储层润湿性的改善非常有利。     

基于扩展毛管数理论的化学驱相渗曲线研究

为了体现润湿性和孔隙结构对表活剂驱渗流特征的影响,在传统毛管数理论的基础上,通过物理模拟与数学处理相结合,提出了低渗透油藏包含润湿性和孔隙结构特征的扩展毛管数理论模型,并通过试验获得了不同低渗岩心对应的扩展毛管数与残余油饱和度,绘制了两者之间的关系图版,据此建立了基于扩展毛管数的相渗曲线非线性处理方法,并进行了油藏工程应用。研究表明,扩展毛管数理论能够体现出低渗透油藏中润湿性和孔隙结构的影响,而低渗透油藏化学驱油需要降低界面张力和改变储层润湿性的共同作用。扩展毛管数与残余油饱和度具有非线性递减函数关系,并只有当其超过临界值时,残余油饱和度才会随其增加而大幅度地下降。基于扩展毛管数的残余油饱和度非线性表征方法,与实验计算结果吻合很好。低渗透油藏化学驱相渗曲线处理新方法能够体现润湿性的影响和表活剂体系的驱替特征,为低渗透油藏化学驱油藏工程和数值模拟研究提供了依据。     

AGGREGATION OF ASPHALTENES OBTAINED FROM A BRAZILIAN CRUDE OIL IN AROMATIC SOLVENTS

Abstract

Surface and interfacial tensions in model systems formed by a Brazilian crude oil n-pentane insolubles (C5I) and n-heptane insolubles (C7I) in three different aromatic solvents: toluene, pyridine and nitrobenzene, were measured at room temperature, employing an automatic tensiometer and using the ring method. The results obtained indicated possible asphaltene aggregation and allowed the determination of critical micelle concentrations (c.m.c) for both C5I and C7I fractions in each of the three solvents considered. In toluene and pyridine solutions, the C5I fraction consistently presented higher c.m.c. values indicating a lower tendency of association for the organic fraction contained in the C5I, and absent in the C7I. In nitrobenzene solutions, this extra organic fraction appears to facilitate asphaltene association, possibly due to the formation of mixed aggregates. Average molecular areas for asphaltenes adsorbed at different interfaces were estimated using measured tensions and found to be in agreement with literature values and suggest a the flatwise surface adsorption of asphaltene molecules. This is consistent with the currently accepted stacking aggregation mechanism of asphaltenes.     

REVERSIBILITY AND INHIBITION OF ASPHALTENE PRECIPITATION IN BRAZILIAN CRUDE OILS

A fundamental understanding of the aggregation and precipitation of asphaltenes in petroleum crudes is important for the development of preventive and curative measures for the potential problem of asphaltene deposition occurring during production, transport and refining operations. The question of reversibility of asphaltene precipitation, yet a controversial issue, is crucial for a clear and unequivocal understanding of the precipitation phenomenon, development of mathematical models that describe the behavior of asphaltenes in petroleum fluids, and the design of inhibitors. In this work, the behavior of precipitated asphaltenes in Brazilian crude tank oil samples following flocculant removal and gradual addition of fresh oil was investigated. The results obtained revealed a re-dissolution of precipitated asphaltene particles following flocculant removal and oil addition. On the inhibition of asphaltene precipitation, the capacity of a number of surfactants and block copolymers to inhibit asphaltene precipitation and deposition was also examined. Ethoxylated Nonylphenols and Hexadecyl Trimethyl Ammonium Bromide displayed highest capacity in the inhibition of asphaltene deposition.     

无机盐与沥青质的协同作用对油藏润湿性的影响

选用两种原油沥青质样品,对沥青质在岩石孔隙表面吸附所引起的润湿性改变进行了实验研究。测定结果表明,岩样润湿性改变的程度主要与沥青质的来源和岩样所含盐水的组成有关。盐水中无机阳离子的类型对沥青质所引起的油藏岩石润湿性改变有十分重要的作用。在浓度相同的情况下,阳离子价数越高,对润湿性的影响越大。盐水中的无机阴离子对沥青质引起的润湿性改变影响很小。在油气开采过程中,地层水和注入水的离子组成,特别是所含阳离子的类型,是影响油藏岩石润湿状态的一个不可忽视的因素。     

REVERSIBILITY AND INHIBITION OF ASPHALTENE PRECIPITATION IN BRAZILIAN CRUDE OILS

ABSTRACT

A fundamental understanding of the aggregation and precipitation of asphaltenes in petroleum crudes is important for the development of preventive and curative measures for the potential problem of asphaltene deposition occurring during production, transport and refining operations. The question of reversibility of asphaltene precipitation, yet a controversial issue, is crucial for a clear and unequivocal understanding of the precipitation phenomenon, development of mathematical models that describe the behavior of asphaltenes in petroleum fluids, and the design of inhibitors. In this work, the behavior of precipitated asphaltenes in Brazilian crude tank oil samples following flocculant removal and gradual addition of fresh oil was investigated. The results obtained revealed a re-dissolution of precipitated asphaltene particles following flocculant removal and oil addition. On the inhibition of asphaltene precipitation, the capacity of a number of surfactants and block copolymers to inhibit asphaltene precipitation and deposition was also examined. Ethoxylated Nonylphenols and Hexadecyl Trimethyl Ammonium Bromide displayed highest capacity in the inhibition of asphaltene deposition.     

低渗透油藏渗流物理特征的几点新认识

对于低渗透油藏,油水界面张力、岩石润湿性和孔喉比是影响产量和采收率的重要因素,而润湿指数和润湿角通过毛管数与驱油效率有直接的定量关系。该文提出了一个关联着界面张力、润湿性和孔喉比的修正毛管数概念,建立了基于Amott润湿指数与USBM指数的润湿角表征方法,继而推导出低渗透储层毛管数表达式,并通过岩心实验确定出其与残余油饱和度的关系。以此为基础给出不同界面张力与润湿情况下的相对渗透率曲线、驱油效率和注入能力的计算公式,揭示了各种油藏物理参数之间的关联性,为优化低渗透油层化学驱改变界面张力、润湿性控制参数,进而为提高驱油效率和采收率提供了理论依据。     

Numerical Simulation of Surfactant Flooding in Darcy Scale Flow

One of the methods that is used nowadays in enhanced oil recovery is surfactant flooding. The main mechanisms of surfactant flooding in reservoir consist of reduction of interfacial tension between water and oil and modification of rock wettability. In this study, the authors simulate the surfactant injection process in Darcy scale and in one-dimensional, multicomponent, multiphase state, and effects of physical phenomena such as adsorption, dispersion, convection, and exchange between fluids and solids are considered. Wettability alteration of reservoir rock due to presence of surfactant in injected fluid is detected in relative permeability and capillary pressure curves. First, the authors express the governing flow equations in the system and then discretize them. The variables consist of water and oil saturations, surfactant concentration in water phase, water and oil pressures, and velocities in each block. Second, the discretized equations are solved by IMPES method and pressure and saturation variables are calculated and after that, the concentration of surfactant in water phase is calculated. Finally, results of simulation are shown.     

The control of asphaltene precipitation in oil wells

Asphaltene instability can occur in petroleum reservoirs leading to permeability reduction and deposition in transportation pipes restricting fluid flow. In this work, effect of reservoir pressure on amount of asphaltene precipitation was investigated. Two different asphaltene inhibitors (a new developed and an industrial) were used for preventing asphaltene deposition under static and dynamic conditions. Viscosity measurements of the oil, core flooding experiments and transmittance measurement were conducted to understand asphaltene precipitation and deposition behavior as well inhibitor efficiencies. Optimum concentration of the new asphaltene inhibitor was 200 ppm. Experiments show inhabitation efficiency of new inhibitor can reach up to 90% and showed better performance when compared with industrial one. In addition, squeeze lifetime of new inhibitor was 1.86 times longer than the industrial inhibitor in carbonate core samples. In the presence of new inhibitor formation damage and percent of transmittance was lower than in the presence of industrial asphaltene inhibitor.