Experimental Investigation into the Screening of New Surfactant Flowback Aids and Statistical Interpretation of Their Imbibing Capacity for Selected Core Substrates

Spontaneous imbibition is a pervasive part of many natural and industrial processes. As an inherent feature of fluid transport in porous media, it is a driver for oil recovery. Understanding spontaneous imbibition and leveraging surface science is fundamental for fluid recovery; specifically, the role of the surfactant in the imbibition processes and the potential to alter capillarity and wettability of reservoir rock. Surfactant success relies on the understanding of the factors governing the interfacial phenomena among crude oil, and formation properties under reservoir conditions. Developing a methodology coupling chemical performance with analytical techniques, and statistical interpretation of core/surfactant/oil interactions, can help establish workflows to advance new chemistries and enhance oil recovery. This article discusses a study of flowback aids formulated as microemulsions corresponding to the thermodynamically stable Winsor Type IV solutions. Neat formulated microemulsions, when dosed at field treatment concentrations, provide either oil-in-water droplet microemulsions or nanoemulsions. The solvency potential was measured, and the Kauri-butanol (Kb) value was determined. Parameters such as critical micelle concentration (CMC) and interfacial tension (IFT) were determined to characterize microemulsion solutions. These systems were tested using either in the column flow test with formation material sieved to match mineral grain size, or sandstone cores of various permeabilities. The results indicate that surfactant-based flow-enhancing aids are desirable for improved oil recovery when compared to the control fluid. The statistical analysis of core-fluid interaction includes an ANOVA followed by assumption evaluations and model interpretation, which demonstrates that the core permeability term, followed by the surfactant term, has the highest contribution whereas oil has no statistical significance to the model.     

宝浪油田提高原油采收率技术研究

分子膜驱油技术是目前石油业提高采收率研究的一个重要方向。其核心就是它与储层岩石接触后,由于在岩石表面的吸附、滞留和捕集作用,使储层表面的润湿性发生变化,从而达到驱替残余油、提高原油采收率的效果。例如由强亲油向弱亲油、中性,甚至亲水性变化时,不仅原油的采出程度有大幅度的提高,而且对于低渗透储层,特别是超低渗透的储层来说,也由于注入性和注入能力的提高而可以进行理想的水驱或化学驱。本文结合宝浪油田低渗储油层的实际情况通过对分子膜剂性能的评价,筛选出了适合宝浪油田低渗储层的分子膜剂类型和浓度。     

A new surfactant wettability alteration model for reservoir simulators

Surfactants enhance oil recovery in naturally-fractured oil-wet rocks by wettability alteration and interfacial tension reduction. The oil-wet state is ascribed to the adsorption of soap on the rock surface. Soaps are the dissociated forms of carboxylic acids in the crude oil, that is, carboxylate surfactants. This paper describes a new mechanistic surfactant wettability alteration model that was developed for and implemented in a reservoir simulator. The model captures the geochemical reactions of acid/soap, the formation of mixed micelles, Henry's law adsorption, and the formation of cationic surfactant-anionic soap ion-pairs. A new wettability scaling factor is used to interpolate between the oil-wet and water-wet relative permeability and capillary pressure curves. The new model also accounts for the effect of salinity and pH, so it should also be useful for modeling low-salinity flooding without surfactant. Previous surfactant wettability alteration models ignored the underlying mechanisms and were not predictive. Simulations of both static and dynamic imbibition were performed to better understand the key surfactant parameters and the dynamics of wettability alteration, microemulsion phase behavior, and interfacial tension reduction on oil recovery. Optimizing surfactant formulations for wettability alteration is discussed.     

酯类微乳液的相变过程中电导率和黏度分析

以月桂酸聚氧乙烯和聚乙二醇二油酸酯为乳化剂,以油酸酯为油相,制备了不同乳化剂配比和不同油相含量的微乳液,研究了乳液浓度对其电导率和黏度的影响。结果表明,随着微乳液浓度的增大,乳液出现由水包油（O/W）型转变为油包水（W/O）型的相变过程;其伴随的电导率变化和黏度变化有着对应的关系：当电导率升高至平稳阶段对应于黏度的缓慢上升阶段,乳液属于O/W型;当电导率急剧下降阶段对应于黏度的突变阶段,乳液处于相转变（O/W和W/O共存）阶段;当电导率很低且缓慢下降阶段对应于黏度缓慢下降的阶段,乳液属于W/O型;此外,聚醚类化合物可明显降低乳液相转变过程的黏度,其中异构醇聚醚的效果最佳,在添加量为0.5 %（质量分数,下同）时,黏度降低的程度最大。     

Surfactant-Induced Wettability Alteration of Oil-Wet Sandstone Surface: Mechanisms and Its Effect on Oil Recovery

Different analytical methods were utilized to investigate the mechanisms for wettability alteration of oil-wet sandstone surfaces induced by different surfactants and the effect of reservoir wettability on oil recovery. The cationic surfactant cetyltrimethylammonium bromide (CTAB) is more effective than the nonionic surfactant octylphenol ethoxylate (TX-100) and the anionic surfactant sodium laureth sulfate (POE(1)) in altering the wettability of oil-wet sandstone surfaces. The cationic surfactant CTAB was able to desorb negatively charged carboxylates of crude oil from the solid surface in an irreversible way by the formation of ion pairs. For the nonionic surfactant TX-100 and the anionic surfactant POE(1), the wettability of oil-wet sandstone surfaces is changed by the adsorption of surfactants on the solid surface. The different surfactants were added into water to vary the core surface wettability, while maintaining a constant interfacial tension. The more water-wet core showed a higher oil recovery by spontaneous imbibition. The neutral wetting micromodel showed the highest oil recovery by waterflooding and the oil-wet model showed the maximum residual oil saturation among all the models.     

Laboratory Studies to Determine Suitable Chemicals to Improve Oil Recovery from Garzan Oil Field

Garzan oil field is located at the south east of Turkey. It is a mature oil field and the reservoir is fractured carbonate reservoir. After producing about 1% original oil in place (OOIP) reservoir pressure started to decline. Waterflooding was started in order to support reservoir pressure and also to enhance oil production in 1960. Waterflooding improved the oil recovery but after years of flooding water breakthrough at the production wells was observed. This increased the water/oil ratio at the production wells. In order to enhance oil recovery again different techniques were investigated. Chemical enhanced oil recovery (EOR) methods are gaining attention all over the world for oil recovery. Surfactant injection is an effective way for interfacial tension (IFT) reduction and wettability reversal. In this study, 31 different types of chemicals were studied to specify the effects on oil production. This paper presents solubility of surfactants in brine, IFT and contact angle measurements, imbibition tests, and lastly core flooding experiments. Most of the chemicals were incompatible with Garzan formation water, which has high divalent ion concentration. In this case, the usage of 2-propanol as co-surfactant yielded successful results for stability of the selected chemical solutions. The results of the wettability test indicated that both tested cationic and anionic surfactants altered the wettability of the carbonate rock from oil-wet to intermediate-wet. The maximum oil recovery by imbibition test was reached when core was exposed 1-ethly ionic liquid after imbibition in formation water. Also, after core flooding test, it is concluded that considerable amount of oil can be recovered from Garzan reservoir by waterflooding alone if adverse effects of natural fractures could be eliminated.     

Triton X-100/正构醇/石油醚/水反相微乳液性质的研究

通过测定微乳液的电导率值,确定配制W/O型Triton X-100/正构醇/石油醚/水微乳液的最大增溶水量;根据微乳液含水量与电导率关系曲线及体系的拟三元相图,讨论了正构醇种类、正构醇含量、乳化剂与油相质量比对W/O型微乳液的结构、电导率、增溶水量的影响。结果表明:乳化剂与油相质量比大于1时,正戊醇、正己醇和正庚醇为助剂配制的Triton X-100/正构醇/石油醚/水体系微乳液有较大的增溶水量,而乳化剂与油相质量比大于1.5时,以正丁醇为助剂配制的Triton X-100/正构醇/石油醚/水体系微乳液才有较大的增溶水量;正构醇的链长及加入量影响微液滴界面膜的强度,从而影响微乳液的增溶水量、电导率及微乳液形成区域的大小;对于Triton X-100/正构醇/石油醚/水体系,正戊醇是形成W/O型微乳液的较好助剂,当正戊醇与Triton X-100的质量比为0.5时,W/O型微乳液的形成区域最大。     

Solubilization of lycopene in jojoba oil microemulsion

The unique properties of jojoba oil make it an essential raw material in the manufacture of cosmetics. New, totally dilutable U-type microemulsions of water, jojoba oil, alcohols, and the nonionic surfactant polyoxyethylene-10EO-oleyl alcohol (Brij 96V) have been formulated recently. Here, these microemulsions are shown to be capable of solubilizing lycopene, a nutraceutical insoluble in water and/or oil, much more effectively than the solvent (or a solvent and surfactant blend) can dissolve them. In water-in-oil (W/O) and oil-in-water (O/W) microemulsions with 10 and 90 wt% water, respectively, the normalized maximal solubilization efficiency α is ca. 20-fold larger than its solubility. The solubilization capacity of the system is mainly surfactant-concentration dependent. The lycopene resides at the interfaces of the W/O and O/W microemulsions and engenders significant structural changes in the organization of the microemulsion droplets. In the absence of lycopene, the droplets are spherical; when lycopene is added, compaction of the droplets and formation of threadlike droplets are observed. On further addition of lycopene, the bridging effect wanes and the droplets revert to a spherical shape. The enhanced solubilization demonstrated for lycopene opens up new options for formulators interested in making liquid and transparent products for cosmetic or pharmaceutical uses.     

裂缝性致密油藏润湿性提高采收率技术研究

在裂缝性致密储层中,水驱效率往往由水自发吸入含原油基质块控制。当基质是原油润湿或中性润湿时,原油很难通过自发渗吸采出。研究目的是确定可以添加到注入水并提高深吸效率的表活剂组合。通过评价几种表活剂在储层温度和矿化度下的水稳定性并在富含粘土的砂岩上测量接触角,对储层岩心进行渗吸试验。结果表明使用一定浓度的表活剂溶液可实现矿物板的润湿反转。之后通过在致密油湿或中性润湿砂岩岩心上进行的自发吸入试验获得较润湿反转前68%的渗吸增量。同时数值模拟的研究也证实随着润湿性的变化,原油回收率也发生明显改变,且与断裂密度和原油粘度相关。     

槐糖脂用于含油砂质土壤处理及石油资源回收

模拟了以生物型表面活性剂槐糖脂配制水溶液和微乳液对原油污染土壤进行处理并回收原油的实验，通过对比证明槐糖脂微乳液对含油土壤的原油脱除效果优于其水溶液，分析了槐糖脂、NaCl、丙三醇的添加量对原油脱除效果的影响，并筛选出3种微乳液配方。将原始原油、土壤与3种配方微乳液回收的原油、土壤进行理化性质对比发现：回收土壤的pH略高且大致呈中性，黏粒体积分数减少，zeta电位无明显变化，微乳液处理对土壤的理化性质影响较小；回收原油中饱和分含量升高，芳香分、胶质和沥青质含量降低，灰分含量增加，密度增大，黏度降低，表明回收原油具备一定的经济使用价值。将3种配方微乳液进行温度和循环利用实验以检验原油脱除效果的稳定性，结果表明：随着温度的升高，微乳液对含油土壤的原油脱除率先升高后趋于稳定，微乳液循环使用5次，对含油土壤的原油脱出率仍在60%以上，其中配方槐糖脂10%、丙三醇3.5%、NaCl 2.5%、柴油19.2%的微乳液处理含油土壤的稳定性最好。     

Enhanced Wettability Alteration by Surfactants with Multiple Hydrophilic Moieties

The main production mechanism during water flooding of naturally fractured oil reservoirs is the spontaneous imbibition of water into matrix blocks and resultant displacement of oil into the fracture system. This is an efficient recovery process when the matrix is strongly water-wet. However, in mixed- to oil-wet reservoirs, secondary recovery from water flooding is often poor. Oil production can be improved by dissolving low concentrations of surfactants in the injected water. The surfactant alters the wettability of the reservoir rock, enhancing the spontaneous imbibition process. Our previous study revealed that the two main mechanisms responsible for the wettability alteration are ion-pair formation and adsorption of surfactant molecules through interactions with the adsorbed crude oil components on the rock surface. Based on the superior performance of surfactin, an anionic biosurfactant with two charged groups on the hydrophilic head, it was hypothesized that the wettability alteration process might be further improved through the use of dimeric or gemini surfactants, which have two hydrophilic head groups and two hydrophobic tails. We believe that when ion-pair formation is the dominant wettability alteration mechanism, wettability alteration in oil-wet cores can be improved by increasing the charge density on the head group(s) of the surfactant molecule since the ion-pair formation is driven by electrostatic interactions. At a concentration of 1.0 mmol L⁻¹ a representative anionic gemini surfactant showed oil recoveries of up to 49% original oil-in-place (OOIP) from oil-wet sandstone cores, compared to 6 and 27% for sodium laureth sulfate and surfactin, respectively. These observations are consistent with our hypothesis.     

Effect of Branched Alcohols on Phase Behavior and Physicochemical Properties of Winsor IV Microemulsions

The microemulsion phase behavior and physicochemical properties of surfactant–water–alcohol–oil systems are the pioneer laboratory study as a function of alcohol, water content and temperature to develop an experimental investigation for a better understanding of the microstructure of a single phase microemulsion and its stability under reservoir condition during hydraulic fracturing to recover the residual trapped oil. Viscosified surfactants are used as an efficient proppant conducting medium in hydraulic fracturing applications. The physicochemical properties of microemulsions are very helpful for characterization of microemulsions to justify their abilities and screening of surfactants. In the study, two branched alcohols, 2-methyl butan-2-ol, 3-methyl butan-1-ol selected as the cosurfactant in the proposed microemulsion system and their effect in tailoring the viscosity of microemulsions were studied. Microemulsion regions elucidated from Winsor’s pseudophase model of an oleate surfactant show a signatory distribution pattern of components between different domains with non-polar and asymmetric geometry of cosurfactant directs macromolecular alignments; their alignment contributes to a viscous microemulsions (gel) regime. The effect of surfactant and alkali, and the experimental temperature on the rheological properties of the lamellar mesophase were investigated. Phase transit regions and exact microemulsion and viscous microemulsion magnitudes were elucidated with the help of conductivity and viscosity studies of the ternary system as a function of the aqueous fraction and were in good agreement with Winsor’s pseudophase model. Dynamic and steady shear rheological studies showed that the gel is viscoelastic in nature, sustain viscosity and elastic modulus values appropriate for proppant suspension under high shear conditions. The proppant suspension and thermal behavior of ideal gel composition was found to be suitable for Coal Bed Methane and soft rock, clay reservoir stimulation.     

Wettability alterations due to crude oil composition and an anionic surfactant in petroleum reservoirs

In this study, dual-drop dual-crystal (DDDC) contact-angle measurements have been made using dolomite rock and fluid samples from the Yates reservoir (West Texas) and in the presence of an anionic (ethoxy sulfate) surfactant. The experiments have been conducted at Yates reservoir conditions (4.8 MPa and 27.8°C) and using live synthetic oil to provide realistic measurements of in situ reservoir wettability. Stocktank crude oil has also been used at reservoir conditions to study the oil compositional effects on wettability. An advancing contact angle of 152° measured for Yates dolomite rock, stocktank oil and synthetic reservoir brine showed a strong oil-wet nature. However, experiments with Yates live synthetic oil resulted in an advancing contact angle of 55°, indicating a weakly water-wet behavior. In the rock-fluids system consisting of Yates stocktank oil, the surfactant altered the wettability to less oil-wet by decreasing the advancing contact angle to 135°. For rock-fluids system with Yates live synthetic oil, the surfactant altered the wettability from weakly water-wet to strongly oil-wet by increasing the advancing contact angle from 55° to 165°. The oil-wet behavior observed with Yates live synthetic oil due to the surfactant indicates a significant wettability altering capability of the surfactant.     

纳米流体对储层润湿性反转提高石油采收率研究进展

储层岩石的润湿性对于石油采收率至关重要,近年来纳米流体润湿反转技术在提高石油采收率方面的应用得到了广泛关注,并取得了一系列成果。本文首先介绍了利用纳米流体对储层润湿性反转在提高石油采收率方面的应用,包括提高水驱效率和降压增注,其次归纳了润湿性变化的实验评价方法并分析影响纳米流体润湿反转效果的因素,表明纳米材料性质（类型、尺寸、浓度）和地层环境（温度、矿化度）均有不同程度的影响。然后阐述了纳米流体改变储层润湿性的机制,认为其包含纳米流体润湿铺展和纳米颗粒岩石壁面吸附的双重机制。最后指出运用此技术存在的问题和难点,并对以后的研究方向进行了展望。     

The use of inorganic sacrificial agents in combination with surfactants in enhanced oil recovery

Current literature on optimization of surfactants in enhanced oil recovery is summarized. Effectiveness of the use of surfactants in chemical EOR processes is dependent on many factors. Uncontrollable factors such as reservoir parameters, minerology, and the nature of the crude oil influence the choice of a chemical process. Each reservoir offers a different set of problems to be solved. When the use of a surfactant is warranted, one attempts to optimize further the activity of this surfactant by modifying the chemistry of the reservoir system. Cost aside, maintenance of optimal surfactant activity is essential to minimize the oil/water interfacial tension. Also, loss of surfactant activity due to adsorption on substrate material is particularly disadvantageous because the water wet nature of the rock may be decreased. The use of alkaline, weak acid anions, such as sodium silicate, phosphate and carbonate to enhance surfactant effectiveness has been studied. These sacrificial agents can reduce the hardness (divalent cation) activity of the solution and compete with surfactant for active sites on the reservoir rock surface. Core flood results show that there is an inverse correlation between surfactant retention in the core and residual oil recovery. They also suggest that surfactants may be recovered for reinjection by the optimal use of sacrifical agents-in particular, the sodium silicates.     

Performance of sea water dilution on the surface free energies of the crude oils in water-flooded carbonate rock

Although several investigations have studied the low-salinity water injection (LSWI) performance during the past decades, the effect of crude oil type on the interfacial tension (IFT) and wettability alteration is still in dark. In this regard, this study is aimed to obtain the thermodynamic energies including adhesion, cohesion and spreading coefficient during LSWI. To achieve this goal, IFT and static contact angle values of three different crude oils (i.e. light, medium and heavy) are measured as a function of sea water salinity. The obtained results revealed that the dilution of sea water can change the wettability of reservoir rock from oil wet state towards water wet state, while crude oil type implies no significant effect on the wettability alteration. Besides, the results illustrated that although the dilution of sea water unfavorably changed the IFT of light and heavy crude oils, it could favorably change the spreading coefficient.     

Effect of Alkyl Sulfate on the Phase Behavior of Microemulsions Stabilized with Monoacylglycerols

In this study the effect of an anionic surfactant (sodium dodecyl sulfate SDS) and oils (hydrocarbons: C12–C16) on the formation and phase behavior of the systems of oil/monoacylglycerols (MAG):SDS/propylene glycol/water has been investigated. The effects of the surfactant mixture on the phase behavior and the concentration of water or oil in the systems were studied at three temperatures (50, 55, 60 °C). Electrical conductivity measurement, FT-IR spectroscopy and differential scanning calorimetry methods were applied to determine the structure and type of the microemulsions formed. The dimension of microemulsion droplets was characterized by dynamic light scattering. It has been stated that the concentration of SDS has a strong influence on the shape and extent of the microemulsion areas. Addition of an ionic surfactant to the mixture with MAG promotes an increase in the area of microemulsion formation in the phase diagrams, and these areas of the isotropic region change with the temperature. It was shown that the presence in the systems of a surfactant more hydrophilic than MAG caused an increase in water content in the microemulsions. It was found that, depending on temperature and concentration of the surfactant mixture, it was possible to obtain a W/O type microemulsion with a dispersed particles size distribution ranging from 20 to 50 nm and containing about 17–38% water in the system. Among different alkanes (from C12 to C16), hexadecane embedded microemulsions showed a maximum water solubilization capacity.     

表面活性剂驱油效率的影响因素研究

在83℃下测定了3种表面活性剂DL-S、HL-Y/NNR、GZ-16的油水界面张力、乳化能力以及改变油藏岩石润湿性的能力。利用低渗透岩心驱油实验研究表面活性剂的这3种特性对驱油效率的影响。结果表明,表面活性剂的浓度在1 000 mg/L时,DL-S的油水界面张力达到10-3mN/m超低数量级,HL-Y/NNR表现出较为优越的乳化性能,GZ-16具有较好的润湿性能。在驱油实验中,具有最好乳化性能的HL-Y/NNR提高采收率的幅度最大为12.91%,其次为具有超低界面张力的DL-S,相较而言,改变润湿性的能力对驱油效率的影响最小。     

Compositional Dependence of Wetting and Contact Angles in Solid‐Liquid‐Liquid Systems under Realistic Environments

The Dual Drop Dual Crystal (DDDC) contact angle measurement technique has been used in this study with a high‐pressure high‐temperature optical cell apparatus to measure dynamic contact angles in rock‐oil‐brine systems at realistic reservoir conditions of temperature and pressure. The experimental observations with live, stocktank, de‐asphalted and de‐resined crude oils indicate that the stability of oil, which determines the precipitation of asphaltenes for wettability alteration, is controlled by the entire oil composition. The ionic interactions caused by the brine composition and surface charged behaviour of rock substrates have been identified as another main mechanism that can affect wetting and contact angles in solid‐liquid‐liquid systems.     

高温分子膜驱油剂驱油效果实验研究

分子膜驱油剂是一种新型驱油剂,它主要是使岩石表面亲油性转为中性,从而剥离油膜,通过自发吸附作用驱替出孔隙内的残余油。分子膜剂的优点有驱油效率好、不污染储层、价格低、投资少。本次研究结果可以看出分子膜驱能够在水驱不出油的情况下继续驱替出原油。本次实验使用了1%、0.5%、0.25%三种浓度的分子膜剂。实验表明分子膜浓度0.5%提高采收率最明显。