Wettability Modification of Fractured Carbonates Using Sodium Metaborate Part II: History Match Results and Sensitivity Simulations

Abstract

Chemical-based wettability modification has become important for the worldwide abundance of fractured carbonates with the potential to enhance water imbibition to expel more oil from a matrix to the fractures. A systematic experimental and modeling approach on the combined benefit of wettability alteration for enhanced water imbibition and interfacial tension reduction is presented. Brine, alkali, and alkali–surfactant solutions are injected sequentially to improve oil recovery from a fractured mixed-wet carbonate core. The experiment was successfully modeled with a 3D chemical flooding reservoir simulator with wettability alteration capability. Part I discussed the laboratory results and presented the modeling approach and the waterflood history match results. The history match procedure and results for wettability modification using an alkali agent and interfacial tension (IFT) reduction with surfactant are discussed in this article. Sensitivity simulations to some key parameters are also presented.     

不同润湿性条件下适合于不同渗透率油层的超低界面张力驱油体系

研制了无碱无聚合物且界面张力达到10^-3mN/m超低值的表面活性剂驱油体系,对于岩石表面润湿性条件为强亲油、中亲油、弱亲油以及强亲水情况,随着渗透率的增加,该体系的采收率逐渐增加.当渗透率增加到某个值时,随着渗透率的增大采收率迅速提高;然后随着渗透率的进一步增大,采收率增加幅度明显降低,将采收率不再增加时的渗透率值称为临界渗透率值.岩石表面亲水性越强,临界渗透率越低,适合于超低界面张力驱油体系的渗透率越小.实验表明,随着岩石表面亲水性的增加,可以使残余油滴活化的最小孔喉半径或渗透率明显降低,在低渗透率、特低渗透率以及超低渗透率的条件下,可将残余油驱替出来.因此,超低界面张力驱油体系不仅适合于中、高渗透率的油层,在一定条件下还可用于低、特低和超低渗透率的油层.     

Recent advances in application of nanotechnology in chemical enhanced oil recovery: Effects of nanoparticles on wettability alteration,interfacial tension reduction,and flooding

Chemical methods of enhanced oil recovery (CEOR) are applied for improving oil recovery from different kinds of oil reservoirs due to their ability for modifying some crucial parameters in porous media, such as mobility ratio (M), wettability, spreading behavior of chemical solutions on rock surface and the interfacial tension (IFT) between water and oil. Few decades ago, the surfactant and polymer flooding were the most common CEOR methods have been applied for producing the remained hydrocarbon after primary and secondary recovery techniques. Recently, more attention has been focused on the potential applications of the nanotechnology in enhanced oil recovery (EOR). For this purpose, many studies reported that nanoparticles (NPs) have promising roles in CEOR processes due to their ability in changing oil recovery mechanisms and unlocking the trapped oil in the reservoir pore system. This paper presents a comprehensive and up-to-date review of the latest studies about various applications of nanoparticles (NPs) within the surfactant (S), polymer (P), surfactant-polymer (SP), alkaline-surfactant-polymer (ASP) and low salinity waterflooding processes, which exhibits the way for researchers who are interested in investigating this technology. The review covers the effects of nanoparticles on wettability alteration, interfacial tension reduction and oil recovery improvement, and discusses the factors affecting the rock/fluid interaction behavior in porous media through the nanofluid flooding.     

PRODUCING ULTRALOW INTERFACIAL TENSION AT THE OIL/WATER INTERFACE

ABSTRACT

In view of the world-wide shortage of petroleum and the fact that a large amount of residual oil will remain in the reservoir after the primary recovery and water flooding stages, the use of Enhanced Oil Recovery (EOR) methods to recover as much as possible of this residual oil has become increasingly important worldwide. The predominant and most promising EOR technique is the micellar-polymer flooding process which uses a surface active agent (a surfactant) to decrease interfacial tension and hence allows oil to freely move from its original location through the porous media. The purpose of this paper is to present an experimental study of the factors affecting the equilibrium interfacial tension (IFT) at the oil/water interface. A large number of experiments was conducted to study the variations of IFT as a function of many parameters including reservoir temperature, pressure, surfactant concentration, and salinity. An Arabian heavy crude oil was used in the analysis along with three different synthetic surfactants and two formation waters. The pendent drop technique enhanced by video imaging was employed for measuring IFT. It was found that for the ranges of variables considered in this study, IFT decreases with temperature and salinity, increases with pressure, and decreases exponentially with surfactant concentration.     

PRODUCING ULTRALOW INTERFACIAL TENSION AT THE OIL/WATER INTERFACE

In view of the world-wide shortage of petroleum and the fact that a large amount of residual oil will remain in the reservoir after the primary recovery and water flooding stages, the use of Enhanced Oil Recovery (EOR) methods to recover as much as possible of this residual oil has become increasingly important worldwide. The predominant and most promising EOR technique is the micellar-polymer flooding process which uses a surface active agent (a surfactant) to decrease interfacial tension and hence allows oil to freely move from its original location through the porous media. The purpose of this paper is to present an experimental study of the factors affecting the equilibrium interfacial tension (IFT) at the oil/water interface. A large number of experiments was conducted to study the variations of IFT as a function of many parameters including reservoir temperature, pressure, surfactant concentration, and salinity. An Arabian heavy crude oil was used in the analysis along with three different synthetic surfactants and two formation waters. The pendent drop technique enhanced by video imaging was employed for measuring IFT. It was found that for the ranges of variables considered in this study, IFT decreases with temperature and salinity, increases with pressure, and decreases exponentially with surfactant concentration.     

Surfactant induced reservoir wettability alteration: Recent theoretical and experimental advances in enhanced oil recovery

Reservoir wettability plays an important role in various oil recovery processes.The origin and evolution of reservoir wettability were critically reviewed to better understand the complexity of wettability due to interactions in crude oil-brine-rock system,with introduction of different wetting states and their influence on fluid distribution in pore spaces.The effect of wettability on oil recovery of waterflooding was then summarized from past and recent research to emphasize the importance of wettability in oil displacement by brine.The mechanism of wettability alteration by different surfactants in both carbonate and sandstone reservoirs was analyzed,concerning their distinct surface chemistry,and different interaction patterns of surfactants with components on rock surface.Other concerns such as the combined effect of wettability alteration and interfacial tension (IFT) reduction on the imbibition process was also taken into account.Generally,surfactant induced wettability alteration for enhanced oil recovery is still in the stage of laboratory investigation.The successful application of this technique relies on a comprehensive survey of target reservoir conditions,and could be expected especially in low permeability fractured reservoirs and forced imbibition process.     

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.     

油田注水吞吐采油的可行性分析

Graham.J．W．的自吸理论公式揭示了裂缝性油藏自吸水驱油量与基质的物性、润湿性、油水界面张力、原油粘度以及油水接触面积的关系。根据这一理论公式，阐明了注水吞吐采油井应选择地层能量不足、原油粘度低、剩余可采储量高、油层亲水并具有1～2个物性好的主力油层，最好是反韵律所组成的裂缝发育的油组。亲油岩心、高粘度原油的全模拟实验证明，在注入水中加入表面活性剂和粘土防膨胀剂，可有效地保护储层、降低油水界面张力、改变岩石润湿性．可大幅度提高原油采出程度。     

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。      

Enhancement of the imbibition recovery by surfactants in tight oil reservoirs

Hydraulic fracturing technology can significantly increase oil production from tight oil formations, but performance data show that production declines rapidly. In the long term, it is necessary to increase the development efficiency of block matrix, surfactant-aided imbibition is a potential way. The current work aimed to explain comprehensively how surfactants can enhance the imbibition rate. Laboratory experiments were performed to investigate the effects of wettability, interfacial tension (IFT), and relative permeability as the key parameters underlying surfactant solution imbibition. Two different types of surfactants, sodium dodecyl sulfate and polyethylene glycol octylphenol ether, at varied concentrations were tested on reservoir rocks. Experimental results showed that the oil recovery rate increased with increased wettability alteration and IFT and decreased residual oil saturation. A mechanistic simulator developed in previous studies was used to perform parametric analysis after successful laboratory-scale validation. Results were proven by parametric studies. This study, which examined the mechanism and factors influencing surfactant solution imbibition, can improve understanding of surfactant-aided imbibition and surfactant screening.     

脂肪醇聚氧乙烯醚磺酸盐系列表面活性剂的协同效应

为满足高温、高盐油藏三次采油的需求,采用自制的脂肪醇聚氧乙烯醚磺酸盐(NNA)系列作为抗温、耐盐驱油表面活性剂,考察了脂肪醇聚氧乙烯醚磺酸盐系列表面活性剂复配前后原油 矿化水体系界面张力的变化,并讨论了其协同效应,并采用静态吸附实验考察了该系列表面活性剂的吸附性能。结果表明,随着NNA表面活性剂分子中氧乙烯链节数的增加,原油 矿化水体系的油 水界面张力最低值对应的矿化度向着高矿化度方向移动,当氧乙烯链节数适中时,可以获得超低油 水界面张力。同系列表面活性剂复配可以显著改善表面活性剂体系的界面活性,具有明显的协同作用。复配表面活性剂使油 水界面张力达到平衡值的时间大大缩短,拓宽了达到超低界面张力的表面活性剂质量分数范围（003%～015%）,耐盐性能也得到提高,使用单剂时耐盐能力在100 g/L以下,复配后耐盐能力达到100 g/L以上。同系列表面活性剂在油砂上的吸附规律相同,从而降低了表面活性剂被地层色谱分离的可能。     

Detection and Reuse of the Produced Chemicals in Chemical Enhanced Oil Recovery Operations

The alkaline-surfactant-polymer (ASP) floods have been increasingly applied in the oil fields because of their high ultimate oil recovery. However, a major technical challenge is how to reduce the amount and the cost of chemicals used so that ASP floods can become cost-effective as well. On the other hand, field applications show that the chemical concentrations remain relatively high in the produced liquids of ASP floods. Therefore, successful detection and reuse of these produced chemicals can substantially reduce their capital cost and environmental impact. In this article, several experimental methods are developed to detect each chemical and quantify its concentration in the produced liquids. Also re-injection of the produced chemicals is conducted to further enhance oil recovery. First, the respective interactions of alkali, surfactant, and polymer with the oil-brine-sand system are studied. Second, the interfacial tension (IFT) is measured as a function of alkaline concentration by using the axisymmetric drop shape analysis technique for the pendant drop case. In addition, the synergistic effects of alkali and surfactant on reducing the IFT are studied. Third, coreflood tests are performed for alkaline, surfactant, alkaline-surfactant, polymer, and ASP floods to determine their respective tertiary oil recovery. Hence, how each chemical contributes to enhanced oil recovery is better understood. Fourth, the produced chemical concentrations are measured and compared with their injected concentrations to determine the potential of reusing these chemicals in practice. Finally, the follow-up coreflood tests are conducted by re-injecting the produced liquids into a new sand pack or Berea core. The re-injection coreflood test results show that the produced chemicals can be reused to effectively enhance oil recovery.     

Experimental investigation the effect of nanoparticles on micellization behavior of a surfactant: Application to EOR

Chemical stimulation such as surfactant flooding in petroleum reservoirs makes efforts to produce remained oil and improve sweep efficiency by means of different phenomena such as lowering interfacial tension and wettability alteration of reservoir rock. Implementing concentration of surfactant through surfactant flooding is one of the big challenges while interfacial tension between surfactant solution and oil after certain concentration involves little changes such as critical micelle concentration (CMC). This article highlights the effect of nanosilica on CMC of Zyziphus Spina Christi, as sugar-based surfactant, in aqueous solutions for enhanced oil recovery and reservoir stimulation purposes. A conductivity approach was selected to assess the CMC of the introduced surfactant in aqueous solution at 25°C. The influence of nanosilica concentrations on CMC variation of introduced surfactant is considered. It is found that CMC of introduced surfactant decreased while the concentration of the nanosilica increased. Results from this study can aim in optimum condition selection of surfactant flooding as an enhanced oil recovery ends.     

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.     

Detection and Reuse of the Produced Chemicals in Chemical Enhanced Oil Recovery Operations

Abstract

The alkaline-surfactant-polymer (ASP) floods have been increasingly applied in the oil fields because of their high ultimate oil recovery. However, a major technical challenge is how to reduce the amount and the cost of chemicals used so that ASP floods can become cost-effective as well. On the other hand, field applications show that the chemical concentrations remain relatively high in the produced liquids of ASP floods. Therefore, successful detection and reuse of these produced chemicals can substantially reduce their capital cost and environmental impact. In this article, several experimental methods are developed to detect each chemical and quantify its concentration in the produced liquids. Also re-injection of the produced chemicals is conducted to further enhance oil recovery. First, the respective interactions of alkali, surfactant, and polymer with the oil-brine-sand system are studied. Second, the interfacial tension (IFT) is measured as a function of alkaline concentration by using the axisymmetric drop shape analysis technique for the pendant drop case. In addition, the synergistic effects of alkali and surfactant on reducing the IFT are studied. Third, coreflood tests are performed for alkaline, surfactant, alkaline-surfactant, polymer, and ASP floods to determine their respective tertiary oil recovery. Hence, how each chemical contributes to enhanced oil recovery is better understood. Fourth, the produced chemical concentrations are measured and compared with their injected concentrations to determine the potential of reusing these chemicals in practice. Finally, the follow-up coreflood tests are conducted by re-injecting the produced liquids into a new sand pack or Berea core. The re-injection coreflood test results show that the produced chemicals can be reused to effectively enhance oil recovery.     

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。     

大庆油田三元复合驱驱油效果影响因素实验研究

通过岩心物理模拟实验及微观驱油实验,分析了界面张力、三元体系粘度、乳化油滴产生及岩石润湿性对三元复合驱驱油效果的影响规律和影响机理。研究结果表明,油水间平衡、动态界面张力大幅度降低可有效提高三元复合驱驱油效率,进行三元复合驱时,油水界面张力须降到10^-3mN/m数量级;增加体系粘度能够扩大三元复合驱的波及体积,水油粘度比大于2是三元复合驱提高采收率幅度达到20%的必要条件;乳化的油滴产生是三元复合驱提高驱油效率的主要形式,油水界面张力越低、驱替体系粘度越大,乳化油滴的产生能力越强,驱油效果越好;三元复合驱能够驱替亲油岩石表面的油膜,促进岩心润湿性由亲油向亲水转化。     

An evaluation of modified silica nanoparticles’ efficiency in enhancing oil recovery of light and intermediate oil reservoirs

The role of nanoparticles in enhancing oil recovery from oil reservoirs is an increasingly important topic of research. Nanoparticles have the properties that are potentially useful for enhanced oil recovery processes, as they are solid and two orders of magnitude smaller than colloidal particles. This paper presents a comparison between the efficiency of modified silica nanoparticles in enhancing oil recovery from two different Iranian light and intermediate oil reservoirs. The mechanisms used to recover additional oil would be oil–water interfacial tension reduction and wettability alteration. Oil phase contact angles and oil–water interfacial tensions were measured in the absence and the presence of nano fluids’ different concentrations (1–4 g/L). Results showed that the interfacial tension reduces dramatically in the presence of nanoparticles for both light and intermediate oil. In addition oil phase contact angle results showed a transformation of rock wettability from water-wet toward oil-wet condition. However, these nanoparticles are more capable in the reduction of the interfacial tension and the alteration of wettability in the case of light oil reservoir. A comparison between recovery results indicated that these nanoparticles are more efficient in light oil reservoirs and produce more incremental amount of oil after primary and secondary processes.     

A Performance Evaluation of Glycolipid Biosurfactant Synthesized by the Enzyme-catalyzed Method

The practice of enhanced oil recovery (EOR) technique shows that the study and application of biosurfactant flooding system have a vast potential for future development. The authors challenge the traditional idea that the oil displacement surfactant must have ultra low interfacial tension. By changing the wettability of reservoir rock as main target, the glycolipid biosurfactant compounded system was developed by enzyme-catalyzed method in laboratory, and a series of experiments had been done combining with reservoir physical measurement. The properties of the active system were characterized by interfacial characters, disbonded, seepage characteristics, antibiotic property, and oil displacement efficiency.     

鄂尔多斯盆地裂缝性低渗透油藏渗吸驱油研究

裂缝性低渗透油藏储层岩性致密,裂缝发育,非均质性强,注水开发效果差,利用水的自发渗吸作用驱油是一种经济有效的开发手段。文中利用鄂尔多斯盆地延长油田西区采油厂的天然露头岩心,通过自发渗吸实验,研究了边界条件、润湿性、温度、原油黏度、界面张力及渗透率等因素对渗吸驱油作用的影响。实验结果表明:润湿性、黏度、界面张力及渗透率是影响渗吸驱油的主要因素,岩石越亲水,原油黏度越低,渗吸驱油效果越好。对于亲水岩心,渗透率相近时,界面张力为0.04 m N/m时渗吸效果最佳;岩石渗透率差异明显时,渗透率为2.94×10~(-3)μm~2时渗吸效果最佳。实验结果为鄂尔多斯盆地裂缝性低渗透油藏渗吸驱油提供了重要的指导作用。