Wettability and morphology of mica surfaces after exposure to crude oil

Reservoir wettability is determined by interactions between crude oil and mineral surfaces, mediated by an aqueous phase. Contact angles between immiscible fluids have long been used as probes to assess the effective wetting condition of surfaces after exposure to brine and oil, but there is a limit to the amount of information that can be deduced from contact angles in such nonideal conditions.In this study, atomic force microscopy (AFM) has been used to observe mica surfaces treated with a series of crude oils that produce a wide range of wetting conditions—water-advancing contact angles on these surfaces vary from water-wet to oil-wet. In the most water-wet case, the only adsorbed features appear to be small, water-wet particles that are probably inorganic. All of the other oils deposited organic coatings, with varying thickness, morphology, and durability. Weakly water-wet systems exhibited many surface features, but the waitings tended to be unstable and to detach from the surface, especially during AFM scanning in water. The most oil-wet systems exhibited thick, stable organic coatings that were not disturbed by AFM scanning.     

Surface and core wetting effects of surfactants in oil-based drilling fluids

Surfactants are used in oil-based drilling fluids to emulsify water and to ensure that cuttings are wetted by oil. The products used are based on drilling conditions and are essentially the same for traditional oil-based and synthetic oil-based fluids. Although much of these surface active materials adsorb on cuttings and filter cake, it is still likely that core samples are exposed to significant concentrations. Additional contamination can occur in subsequent core tests if the oil samples used are themselves contaminated with the drilling fluid.Commercial surfactant packages from several sources have been selected for examination of their effects on the tests normally used to assess the extent of wetting change in crude oil/brine/mineral systems. These products were characterized with respect to their interfacial properties by measurements of interfacial tension as a function of concentration and brine composition. Wetting tests include measurements of contact angles on smooth mineral surfaces and rates of imbibition into porous media. The results show that even very low concentrations of surfactants, much lower than the amounts recommended for use in drilling fluids, can affect the wetting properties of mica surfaces and Berea sandstone cores.     

表面活性剂吸附引起的硅石润湿性改变

用两相滴定法测定了十六烷基三甲基溴化铵(CTAB)和十二烷基苯磺酸钠(SDDBS)在水湿和油湿硅石(SiO_2)上的吸附量,考察了电解质和pH值对吸附量的影响,用Amott/USBM法测定了这两种表面活性剂引起的砂岩岩样润湿性改变。测定结果表明,阳离子活性剂比阴离子活性剂更容易吸附在水湿硅石表面,导致硅石水湿性明显减弱甚至变为油湿。无机电解质使阴离子活性剂在硅石上的吸附量显著增加,Ca~(2+)与阴离子活性剂间的络合作用有可能使硅石表面从水湿向油湿转化。pH值对CTAB和SDDBS在硅石上的吸附量有相反的影响。     

The adsorption properties of a novel ether nanofluid for gas wetting of tight sandstone reservoir

At present, the most effective means of releasing the ‘water blocking damage’ in the near-well zone is to change the wettability of the rock surface from liquid wetting to gas wetting. Previous studies were limited to rock wettability and liquid phase relative seepage capacity changes, while systematic study on the adsorption properties of chemical agents on rock surfaces was relatively insufficient. In this paper, the wettability of the reservoir rock, the core taken from the tight sandstone of the 105X well in Dibei, was modified to gas wetting using the ether surfactant nano-solution CNDAD1#, and the static and dynamic macroscopic adsorption properties, microscopic adsorption properties, improvement in liquid phase percolation capacity and erosion resistance was systematically evaluated. The results show that the CNDAD1# nano-solution changes the sandstone wettability from liquid wetting to gas wetting. Chemical has a good static adsorption and dynamic adsorption on the surface of rock. SEM microscopic imaging and EDX elemental analysis shows the nano-solution of ether surfactant has good micro-adsorption properties on the surface of rock powder, and the surface roughness of sandstone is invariable, which makes its different from the principle of fluorine-containing gas wetting agent.     

Beneficial effects of wettability altering surfactants in oil-wet fractured reservoirs

In fractured reservoirs, an effective matrix-fracture mass transfer is required for oil recovery. Surfactants have long been considered for oil recovery enhancement, mainly in terms of their ability to reduce oil–water interfacial tension. These surfactants are effective when the fractured formations are water-wet, where capillary imbibition of surfactants from the fracture into the matrix contributes to oil recovery. However, another beneficial aspect of surfactants, namely their ability to alter wettability, remains to be explored and exploited. Surfactants capable of altering wettability can be especially beneficial in oil-wet fractured formations, where the surfactant in the fracture diffuses into the matrix and alters the wettability, enabling imbibition of even more surfactant into the matrix. This sequential process of initial diffusion followed by imbibition continues well into the matrix yielding significant enhancements in oil recovery.In order to test this hypothesis of sequential diffusion–imbibition phenomenon, Dual-Drop Dual-Crystal (DDDC) contact angle experiments have been conducted using fractured Yates dolomite reservoir fluids, two types of surfactants (nonionic and anionic) and dolomite rock substrates. A new experimental procedure was developed in which crude oil equilibrated with reservoir brine has been exposed to surfactant to simulate the matrix-fracture interactions in fractured reservoirs. This procedure enables the measurements of dynamic contact angles and oil–water interfacial tensions, in addition to providing the visual observations of the dynamic behavior of crude oil trapped in the rock matrix as it encounters the diffusing surfactant from the fractures. Both the measurements and visual observations indicate wettability alterations of the matrix surface from oil-wet to less oil-wet or intermediate wet by the surfactants. Thus this study is of practical importance to oil-wet fractured formations where surfactant-induced wettability alterations can result in significant oil recovery enhancements. In addition, this study has also identified the need to include contact angle term in the dimensionless Bond number formulations for better quantitative interpretation of rock–fluids interactions.     

癸烷在二氧化硅表面的油膜形成与表面润湿性

用二氧化硅片作为模拟岩石，以椭圆偏振法测量癸烷在其表面形成的油膜厚度，通过长度测量法测定水在二氧化硅表面的接触角来判断润湿性及润湿性的变化。亲水的二氧化硅表面难以形成油膜，而疏水的二氧化硅表面能形成较厚而稳定的油膜。疏水或近中性的二氧化硅表面在经碱水作用或吸附表面活性剂后，在特定的条件下能变成弱亲水或亲水，从而将油膜破坏。     

The significance of formation damage caused by the adsorption oil-based mud surfactant

Surfactants formulated into oil-based mud emulsifiers can adsorb to pore surfaces causing changes in rock wettability which are widely believed to impair formation permeability when drilling fluid invades the near-wellbore region. This paper describes experimental work undertaken to assess the significance of this mechanism of formation damage caused by oil-based mud emulsifiers commonly used in the North Sea. Wettability alteration, relative permeability reduction to oil (at connate water saturation) and extent of surfactant retention have been measured for a range of initially water wet outcrop sandstones treated with solutions of a commercial emulsifier.The study was then extended to consider the impact of formation damage from actual mud filtrates prepared from 80/ 20 oil based muds. Changes in wettability and relative permeability were measured for mud miltrates containing increasing amounts of commercial emulsifier. Finally, the effect of substituting commercial emulsifier with pure grade surfactant on sandstone wettability and permeability was investigated. Fired outcrop cores were employed in the experiments to evaluate specifically the effect of surfactant adsorption to pore surfaces. The potentially damaging impact of wettability alteration in causing fines mobilization is therefore not within the scope of the present paper.It is concluded from these studies that formation damage caused simply by adsorption of surfactants typically formulated into oil-based muds may be of only minor significance. Although a reasonable correlation between wettability alteration and relative permeability reduction was found, there is evidence to suggest that the damage caused by the oil-based mud emulsifiers was not attributable to wettability effects alone. Pure grade surfactant was found to induce strong changes in sandstone wettability but cause only minor permeability impairment, compared with equivalent amounts of commercial emulsifier. Precipitation of organic material (wax) derived from the commercial emulsifier was identified as contributing significantly to the damage observed.     

微乳助排剂的研制及性能评价

采用两性表面活性剂、双子表面活性剂和非离子表面活性剂作为主剂、添加助剂及油相,复配得到了具有低表面张力和低界面张力的微乳液,并对其粒径、热稳定性、改善水润湿性能力、与压裂液配伍性及返排提高率进行评价,得到了具有优异助排效果的微乳液体系。结果表明:该体系粒径分布约80nm,其表面张力平衡值约26.0mN/m,与煤油间界面张力最低可降至0.1mN/m,可改善云母表面润湿性,与其接触角最高改善约70°,返排提高率最高达到了29.72%;微乳液具有一定的耐温性,且与压裂液、添加剂和破胶液配伍性良好。     

The Influence of Surfactant Solution Injection in Oil Recovery by Spontaneous Imbibition

Imbibition is the spontaneous displacement of fluids through porous media that occurs until capillary equilibrium is reached. Factors such as wettability and high interfacial tensions may negatively affect the process, requiring additional work to enhance oil recovery. This work aims to explain some aspects of the dynamics of oil recovery by spontaneous imbibition using different fluids. Static imbibition and contact angle experiments were performed using sandstones of the Botucatu Formation (Brazil). The plug samples were exposed to immersion in brine and in surfactant solutions, and the progression of oil recovery was monitored with time. The results showed that the capillary imbibition rate and the oil recovery factor were higher when an ionic surfactant was used. The inverse Bond number and the shape of the recovery profile showed different trends of the capillary imbibition dynamics. Higher oil recovery factors for ionic surfactant were also an effect of the contact angles observed.     

Adsorption kinetics of natural surfactants on carbonate minerals in enhanced oil recovery processes

One of the most promising methods for improving oil recovery from carbonate reservoirs is surfactant flooding in which the trapped oil can be mobilized by alteration in the wettability of rock surfaces and also reduction in the interfacial tension between oil and water. Adsorption of surfactants on carbonate minerals plays a key role in designing this process and may make it less effective for enhancing oil recovery. Natural surfactants have been proposed by many researchers since they have lower cost and also less detrimental environmental effects compared to the industrial surfactants. Well-established predictive models for predicting the adsorption of natural surfactants have some issues which need to be addressed. Therefore, developing an accurate, rapid and simple model is crucial. In this study, a least square support vector machine (LSSVM) optimized with coupled simulated annealing (CSA) algorithm is developed for accurate prediction of natural surfactants kinetic adsorption on carbonate minerals. Obtained results by this model were in a very good agreement with experimental results. Additionally, the results showed that the proposed model has the highest accuracy and performance in comparison to the previous kinetic models. Afterward, the effect of natural surfactants adsorption on the amount of oil recovery and also the quality of the produced oil was investigated via core flooding tests for showing the importance of determining the adsorption of surfactants before any surfactant flooding. Results demonstrated that lower surfactants adsorption yields higher oil recovery factor and oil with higher viscosity.     

表面活性剂的润湿性及增注机理研究

研究了改变低渗透砂岩亲水性油气层润湿性对增注性能的影响。通过测定表面张力和润湿角筛选出了常规表面活性剂ABS、OPT以及两性Gemini表面活性剂GC26。通过岩心驱替试验考察了表面活性剂的增注性能和对岩心的油水相对渗透率的影响。结果表明,0.5%ABS、0.1%GC26、0.5%OPT的表面张力分别为25.07、28.33、29.57mN/m。活性剂处理岩心后,岩心表面润湿性向弱亲油方向移动,等渗点时含水饱和度下降,尤其是Gemini表面活性剂GC26,含水饱和度降到48%,显示出孔喉表面转变为亲油,岩心水相渗透率提高幅度达到86.57%,具有较好的增注效果。结合GC26的结构特点及表面性质,分析了表面活性剂增注效果的差异,认为提高吸附膜的致密性及疏水性程度是增注的关键。     

Wettability Alteration of Low-permeable Carbonate Reservoir Rocks in Presence of Mixed Ionic Surfactants

Abstract

Altering the wettability of the carbonate reservoir rocks from oil-wet to water-wet has figured prominently as one of the enhanced oil recovery methods in recent years. The authors measured the effect of different ionic surfactants on the wettability alteration of the rock, saturated with crude oil, and the consequent improvement in oil production was investigated by spontaneous imbibitions of solutions containing cationic, anionic, and cationic-anionic surfactant mixtures. A very low-permeable carbonate rock from one of the Iranian oil reservoirs was selected for this study. The results of imbibition tests were furthermore supported by measuring IFT, taking pictures of producing oil drops from different exterior core plug surfaces and also observing the distribution of the remaining oil in cores at the end of experiments. The results show that cationic surfactants at concentrations higher than CMC can cause a remarkable oil production through alteration of wettability and, moreover, the extent of oil production increases with temperature. In contrast, it is observed that the anionic surfactants are not able to change the wettability of an oil-wet surface and their combination with the cationic type would reduce the oil production potential of cationic surfactants.     

表面活性剂对低渗透油藏渗吸敏感因素的影响

界面张力和岩石润湿性是影响毛细管压力大小的决定性因素,因此研究表面活性剂对这两个因素的影响,可以充分发挥渗吸作用、提高低渗透油田原油的渗吸采收率。利用7块不同渗透率的亲水人造岩心,通过渗吸试验、旋滴法和动态接触角法研究了表面活性剂对油水界面张力、水湿表面润湿性、毛细管压力以及渗吸采收率的影响。试验结果发现:随着表面活性剂RS-1质量分数的增大,油水界面张力先有较大幅度降低后略有升高,最后趋于平稳;表面活性剂具有很强的改变水湿表面润湿性的能力,且能降低毛细管压力、提高渗吸采收率。研究结果表明:表面活性剂降低界面张力效果明显,并且复配表面活性剂降低界面张力的效果比单一活性剂好,岩样渗吸采收率与油水界面张力和毛细管压力的对数呈线性负相关关系。      

Experimental Investigation of Contact Angles Under Oil-Microbial Solution on Carbonate Rocks

Abstract

Contact angles are used to measure the wetting behavior of two immiscible fluids on a solid surface. Fluids are considered wettings if their contact angles with surface are less than 90°, and they are considered nonwetting, if their contact angles are greater than 90°. Because of its influence on other petrophysical properties of reservoir rocks, such as relative permeability, capillary pressure, and the residual oil saturation after a flood, wettability and its direct measure, the contact angle, play a significant role in affecting the recovery from both primary and improved recovery processes. In this work, contact angle alteration occurring in microbial enhanced oil recovery processes (MEOR) are quantified and described, along with a study of the factors that would enhance such contact angle alteration. An experimental method for the measurement of contact angles has been developed in which the contact angle is measured as a function of time. Measurements of contact angle and interfacial tension for four different types of UAE crude oil and four different mineralogical rock composition over a range of microbial concentration, salinity, and temperature are reported. Results showed that contact angles for the studied systems increased with temperature, crude oil sulfur concentration and microbial concentration up to a certain concentration, beyond which the bacteria concentration exhibited no effect on the contact angle. Crude oils containing low asphaltene concentration produced a stable contact angle and oils containing high asphaltene concentration produced surfaces with unstable wettability. The mineralogical composition of limestone rocks had no effect on the contact angle of microbial-oil system.     

The coupling between evaporation and adsorbed surfactant accumulation and its effect on the wetting and spreading behaviour of volatile drops on a hot surface

The role played by surfactants in the wetting process has been extensively studied because of its huge potential applications. The effect of surfactants on wetting behaviour of volatile liquids has not been widely investigated. Superspreading phenomenon has been recently subject to numerous research works. It has been pointed out that Marangoni effect could be a key mechanism behind the superspreading phenomenon. In the present paper, the case of volatile wetting liquids is discussed; it is argued that there is a strong coupling (competition) between spreading and evaporation.The present work presents an experimental investigation of the temperature dependence of the wetting behaviour of droplets having different concentrations of surfactant (Triton X-100) on a heated aluminum surface. The need to investigate the temperature dependence of the contact angle of water stems from several applications involving droplets evaporation. The evaporation of the sessile drops was recorded using a CCD camera and the images were analyzed using the drop shape analysis software. The water drops are found to have a larger initial contact angle than the surfactant sessile drops. That was attributed to surfactants lowering the surface tension. The evaporation rate is strongly affected by the surfactant concentration; in some cases, almost around 75% from the water evaporation rate enhancement is observed. This is attributed to increased heat transfer area of the surfactant drops, as they increase the wetting area. The accumulation of the surfactant near the interface plays a major role in both wetting and evaporation. The concentration of the surfactant along the liquid–vapour interface is not uniform because of non-uniform evaporation; this leads to a solutal Maranfoni effect. The final spreading area when plotted as a function of surfactant concentration is found to exhibit a maximum when surfactant is present. It is thought that evaporation induces gradients in surfactant interfacial concentration leading to observed behaviour. Another interesting result was found in the presence of the surfactant; the spreading area exhibits a maximum when plotted against the substrate temperature. It seems that the evaporation can affect the interfacial surfactant distribution and accumulation leading to the observed results.     

气湿性纳米SiO2颗粒对岩心润湿反转及解水锁机理

使用气湿反转剂能解除凝析气藏等温降压开采过程中产生的液锁损害,但目前的气湿反转剂存在价格高、用量大、气湿反转效果差等缺点。为此,通过采用改进的Stober法制备均一粒径的纳米SiO2颗粒,再对其表面进行功能化修饰,合成出了具备气湿反转功能的纳米颗粒,其最佳合成条件为,正硅酸乙酯和氨水的用量均为1~2 mL,非离子型氟碳表面活性剂FG24的浓度为0.3%。通过接触角法、Owens二液法和自吸吸入法研究了纳米SiO2颗粒对岩心润湿性的影响。研究表明,用0.3%气湿性纳米颗粒流体处理岩心,水相和油相在岩心表面的接触角可由未处理时的23°和0°增至157°和135°;岩心的表面能由67.9 mN/m降至0.23 mN/m;岩心的液相饱和度由87%和73%降至3.5%和32%,水相和油相的自吸速率由0.26和0.27 mL/min在2 h内降至0。实验还测定了气、油相在气(油)-纳米流体-岩心体系中的接触角,探索分析了气湿性纳米SiO2颗粒的作用机理。结果表明,该纳米颗粒具备良好的气湿反转功能。     

双疏性表面处理预防致密储层水相圈闭损害实验研究

传统的屏蔽暂堵技术不能有效防止致密储层中工作液的侵入,而以往靠降低界面张力排驱液相的方法效果短暂。在工作液中加入氟表面活性剂,增大润湿接触角,是一种降低毛管力减弱毛管自吸的新方法。润湿实验筛选出能将致密砂岩由液润湿改变为气润湿的氟表面活性剂。100℃下将岩心片浸泡在含所选氟活性剂的滤液中处理40 min,岩心片与滤液和水的接触角分别为120°和110°。毛管自吸、岩心流动实验表明,处理后岩心总吸水量降低了60%,自吸速率较处理前降低了40%～50%,驱替速率约是处理前的2倍。表明,氟活性剂能够有效改变储层岩心的润湿性,具有预防水相圈闭损害的应用潜力。     

气湿性纳米SiO_2颗粒对岩心润湿反转及解水锁机理

使用气湿反转剂能解除凝析气藏等温降压开采过程中产生的液锁损害,但目前的气湿反转剂存在价格高、用量大、气湿反转效果差等缺点。为此,通过采用改进的Stober法制备均一粒径的纳米SiO_2颗粒,再对其表面进行功能化修饰,合成出了具备气湿反转功能的纳米颗粒,其最佳合成条件为,正硅酸乙酯和氨水的用量均为1~2 m L,非离子型氟碳表面活性剂FG24的浓度为0.3%。通过接触角法、Owens二液法和自吸吸入法研究了纳米SiO_2颗粒对岩心润湿性的影响。研究表明,用0.3%气湿性纳米颗粒流体处理岩心,水相和油相在岩心表面的接触角可由未处理时的23°和0°增至157°和135°;岩心的表面能由67.9 m N/m降至0.23 m N/m;岩心的液相饱和度由87%和73%降至3.5%和32%,水相和油相的自吸速率由0.26和0.27 m L/min在2 h内降至0。实验还测定了气、油相在气(油)-纳米流体-岩心体系中的接触角,探索分析了气湿性纳米SiO_2颗粒的作用机理。结果表明,该纳米颗粒具备良好的气湿反转功能。     

Experimental Investigation of Contact Angles Under Oil-Microbial Solution on Carbonate Rocks

Contact angles are used to measure the wetting behavior of two immiscible fluids on a solid surface. Fluids are considered wettings if their contact angles with surface are less than 90°, and they are considered nonwetting, if their contact angles are greater than 90°. Because of its influence on other petrophysical properties of reservoir rocks, such as relative permeability, capillary pressure, and the residual oil saturation after a flood, wettability and its direct measure, the contact angle, play a significant role in affecting the recovery from both primary and improved recovery processes. In this work, contact angle alteration occurring in microbial enhanced oil recovery processes (MEOR) are quantified and described, along with a study of the factors that would enhance such contact angle alteration. An experimental method for the measurement of contact angles has been developed in which the contact angle is measured as a function of time. Measurements of contact angle and interfacial tension for four different types of UAE crude oil and four different mineralogical rock composition over a range of microbial concentration, salinity, and temperature are reported. Results showed that contact angles for the studied systems increased with temperature, crude oil sulfur concentration and microbial concentration up to a certain concentration, beyond which the bacteria concentration exhibited no effect on the contact angle. Crude oils containing low asphaltene concentration produced a stable contact angle and oils containing high asphaltene concentration produced surfaces with unstable wettability. The mineralogical composition of limestone rocks had no effect on the contact angle of microbial-oil system.     

乳化和润湿反转现象的耗散粒子动力学研究

利用耗散粒子动力学方法,研究了化学驱过程中乳化和润湿反转两个重要的物理化学现象。通过合理划分流体粒子和定义粒子之间相互作用参数,模拟了十二烷基苯磺酸钠、正十二烷和水三组分体系的自发乳化现象;通过附加固壁条件,模拟了在水动力作用下吸附在岩石表面的油珠发生破裂的非自发乳化过程,以及由于表面活性剂在岩石表面吸附而引起的润湿反转现象,比较了润湿反转前后残余油珠的运动情况。模拟结果表明:作为介观力学的离散粒子动力学方法,耗散粒子动力学方法可作为研究包含物理化学现象的化学驱渗流问题的重要手段。