Mechanisms of Enhanced Oil Recovery by Surfactant-Induced Wettability Alteration

Different measurements were conducted to study the mechanisms of enhanced oil recovery (EOR) by surfactant-induced wettability alteration. The adhesion work could be reduced by the surfactant-induced wettability alteration from oil-wet conditions to water-wet conditions. Surfactant-induced wettability alteration has a great effect on the relative permeabilities of oil and water. The relative permeability of the oil phase increases with the increase of the water-wetness of the solid surface. Seepage laws of oil and water are greatly affected by surfactant-induced wettability alteration. Water flows forward along the pore wall in the water-wet rocks and moves forward along the center of the pores in the oil-wet rocks during the surfactant flooding. For the intermediate-wet system, water uniformly moves forward and the contact angle between the oil–water interface and the pore surface is close to 90°. The direction of capillary force is consistent with the direction of water flooding for the water-wet surface. While for the oil-wet surface, the capillary force direction is opposite to the water-flooding direction. The highest oil recovery by water flooding is obtained at close to neutral wetting conditions and the minimal oil recovery occurs under oil-wet conditions.     

Similarities and Differences of Low Salinity Polymer and Low Salinity LPS (Linked Polymer Solutions) for Enhanced Oil Recovery

Linked polymer solution (LPS) is nano-size particles made of hydrolyzed polyacrylamide (HPAM) cross-linked with aluminum citrate. The propagation of LPS has been compared to non-cross-linked polymers at low brine salinity condition. The possible differences in properties and potentials for oil recovery have been investigated using water-wet and intermediate-wet cores. The target oil for polymer flooding (PF) is assumed to be the portion of the reservoir that has been bypassed by water during waterflooding and not the residual oil saturation in flooded zones. Our recent studies have shown that a positive synergy can be obtained by combining low salinity and PF. It has been claimed in the literature that cross-linking polymer such as colloidal dispersion gels (colloidal dispersion gels (CDG), micron-size aggregates) or LPS (nano-size particles) would extend the application of polymers to also include change in residual oil saturation. The results of this study indicated higher pressure buildup when low salinity LPS was propagated through brine saturated cores compared to low salinity polymer solution. The pressure buildup was even stronger for high salinity LPS injection. In two phase flow experiments, both polymer and LPS under low salinity condition, showed approximately similar propagation and oil recovery potential when injected into water-wet and intermediate-wet cores.     

Study on Influencing Factors of Chemical Flooding for Heavy Oil

Alkali and alkali/surfactant displacing agents are designed for two kinds of heavy oil. Results of emulsifying capacity, dynamic interfacial tension (IFT) and water-wet core flooding tests show that, although alkaline/surfactant systems exhibit better capacity in emulsification and IFT reduction, oil recovery values of alkaline/surfactant flooding are lower than those of alkaline flooding. Glass-etched micromodel tests further demonstrate that, when alkaline solution penetrates into the oil phase, water streams break into ganglia coating oil film. Water ganglia may be entrapped by narrow throats, consequently presenting a water-oil alternating slug flow. Similar water ganglia also appears in alkaline/surfactant flooding, however, water channeling along the pore surface occurs subsequently, resulting in its relatively lower oil recovery.     

Spontaneous imbibition of surfactant solution into an oil-wet capillary: wettability restoration by surfactant-contaminant complexation

For a given type of rock, the effectiveness of oil recovery through wettability alteration is highly dependent upon the nature of the water-soluble surfactant used. Different mechanisms have been proposed by others to explain wettability alteration by surfactants, and understanding the process is crucial to improve recovery performance. Known mechanisms include (1) surfactant adsorption onto the oil-wet solid surface (coating mechanism) and (2) surfactant molecules complexing with contaminant molecules from the crude oil which are adsorbed on the rock surface so as to strip them off (cleaning mechanism). With the second mechanism, the wettability is restored by lifting the contaminant layer away, exposing the rock surface which was originally water-wet. We previously focused on the numerical modeling of the surfactant coating mechanism (Hammond and Unsal Langmuir2009, 25, 12591; 2010, 26, 6206), and we now present a numerical study for the cleaning process. Our new model shows that when a wettability altering surfactant solution is allowed to imbibe spontaneously and acts by the cleaning process, the meniscus advances more rapidly than when there was wettability alteration by coating alone. In our previous model there was a concentration threshold below which imbibition was not possible. That threshold arose because a finite amount of surfactant needs to be adsorbed onto the oil-wet surface to change the contact angle to a water-wet value, but the maximum amount that can be absorbed is limited by the requirement that it be in equilibrium with the surfactant concentration near the meniscus. In the new model, with the cleaning mechanism there is no such threshold, since the cleaning process is driven by the surfactant flux into the vicinity of the advancing meniscus rather than the surfactant concentration there. As long as there are surfactant molecules present in the aqueous solution, the flux is nonzero and molecule pairs can form and alter the wettability by removing the contaminant from the oil-wet surface. However, under very low surfactant concentrations, the process is extremely slow compared to at higher concentrations.     

Influence on Emulsification in Binary Flooding of Oil Displacement Effect

As one of the important mechanisms of EOR for SP binary flooding, emulsification attracts much attention of researchers. But there have not yet unified methods or clear understandings of evaluation of the emulsion function on flooding system and emulsification's impact on enhanced oil recovery. A comprehensive evaluation method of emulsifying properties is established in this paper for the first time. It characterizes the emulsifying properties of different flooding system by using the emulsifying integrated index, and examines the corresponding core flooding results of different emulsifying properties. Results of Berea core test show that the flooding system runs better with a higher emulsifying composite index in cores whose permeability is 300 ～ 400 mD. When emulsifying integrated index increases from 23.9% to 80.2%, the corresponding oil displacement efficiency reaches 12%. When emulsifying integrated index is under the medium level of 50% or less, the SP flooding system efficiency increases rapidly with the index changes, then increases slowly. The influencing rule of emulsification of SP binary flooding is obtained in this paper, which is important to optimize the formulation of SP binary flooding system, provide an important basis and technical support for the design of field experiments and SP flooding promotion.     

Improving performances of double-chain single-head surfactants for SP flooding by combining with conventional anionic surfactants

The binary surfactant mixtures of 1,3-dialkyl (diC₈-diC₁₂) glyceryl ether ethoxylates with didodecylmethylhydroxylpropyl sulfobetaine (diC₁₂HSB) are good formulations for surfactant–polymer flooding of Daqing crude oil, China, but suffer from low aqueous solubility. By combining with α-olefin sulfonates (AOS) at small molar fractions, the aqueous solubility of the formulations can be significantly improved due to the formation of charged mixed micelles. The ternary formulations can reduce Daqing crude oil/connate water interfacial tension to ultralow at a wide range of total surfactant concentration (0.625?～?10?mM), have good resistance to adsorption by sandstone, and can keep sandstone surface water-wet.     

Synthesis of Surfactants from Alkali Lignin for Enhanced Oil Recovery

With the cheap and abundant resource of alkali lignin as feedstock, surfactants for enhanced oil recovery were synthesized by amination and alkylation reaction of lignosulfonate. The effects of amination conditions, including the ratio of raw materials, amination reagent, temperature, and reaction time, on nitrogen contents and surface tension of the surfactants were investigated. The results showed that ethylenediamine was more suitable for amination, and the molar ratio of alkali lignin, ethylenediamine, and formaldehyde was 1:2:1.5 at 80°C for 5 hours. The structure of synthesized products was characterized by Fourier transform infrared spectrometry. The HLB value of synthesized product was 10. The interfacial tension between Daqing crude oil and synthetic water could be decreased to 10^?2 mN/m with synthesized surfactant and NaOH at 45°C. Moreover, the effects of molecular weight of surfactants on interfacial tension were also studied. The synthesized surfactant (M_w > 10,000) showed a better interfacial activity on Daqing crude oil.     

Foam Flooding with Ultra-Low Interfacial Tension to Enhance Heavy Oil Recovery

Severe viscous fingering during water flooding of heavy oil leaves a large amount of oil untouched in the reservoir. Improving sweep efficiency is vital for increasing heavy oil recovery. Previous researches have proved that foam flooding can increase the sweep efficiency and oil recovery. The polymers could make the foam more stable and have better plugging capacity, but the interfacial tension (IFT) of oil and water increase which could decrease the displacement efficiency of the heavy oil. In view of the deficiency of conventional foam flooding, it is necessary to research the ultra-low interfacial tension foam which could improve macro-swept volume and micro-displacement efficiency in heavy oil reservoir. In this paper a novel foam agent is developed by the combination of surfactant and additives to lower the IFT of oil and water. The operating parameters including foam injections modes and gas liquid ratio were investigated by core flooding experiments. Field test performance shows that oil production per day increased from 85.6 to 125.7 t, water cut declined from 92.1 to 83.6% after 3 months injection. This study provides a novel method to improve heavy oil recovery with an ultra-low interfacial tension foam flooding system.     

Application of response surface methodology for optimization of the stability of asphaltene particles in crude oil by TiO2/SiO2 nanofluids under static and dynamic conditions

In this work, the onset of asphaltene flocculation for an Iranian crude oil by titration of samples with heptane in the presence and absence of the TiO₂/SiO₂ nanofluids was obtained by Near-IR spectroscopy. Nanoparticles and nanocomposites were characterized by BET, FESEM, EDX, XRD, and XRF analysis. Modeling and optimization of inhibition of asphaltene flocculation process by TiO₂/SiO₂ nanofluids were conducted by response surface methodology (RSM). Under optimum conditions (nanocomposite composition = 0.04 wt% (80%TiO₂:20%SiO₂), salinity = 4.01 wt%, and pH = 3.42), the onset point increased. For nanofluids stability analysis, the optimum nanofluid was compared with the two other nanofluids (SiO₂ and TiO₂) by visual observation method. The results indicated that high stability and surface area of the 80%TiO₂ nanocomposites increase asphaltene adsorption on the particles surface that subsequently increases the onset point. In addition, the optimum nanofluid performance on the carbonate rocks was evaluated by contact angle and core flooding experiments. The 80% TiO₂ nanofluid changed the wettability of carbonate rocks from strongly oil-wet to strongly water-wet condition and also decreased the residual oil saturation and enhanced the oil recovery with an increase in the recovery factor of about 15%.     

Synthesis,Characterization, and Property Evaluation of a Hydrophobically Modified Polyacrylamide as Enhanced Oil Recovery Chemical

A novel hydrophobically modified polyacrylamide p(AM/NaA/OP-10-AC/BOAM) was successfully synthesized via an aqueous micellar copolymerization method from acrylamide (AM), sodium acrylate (NaA), octylphenol polyoxyethylene acrylate (OP-10-AC), and small amounts of N-benzyl-N-octylacrylamide (BOAM), with the aim of investigating the copolymer's rheological behaviors under various conditions such as polymer concentration, shearing, temperature, and salinity. The copolymer was characterized by infrared spectroscopy, scanning electron microscopy, and atomic force microscope. Scanning electron micrographs show large aggregates in solution formed by the association from the hydrophobic groups of the copolymer. Compared with partially hydrolyzed polyacryamide (HPAM), the copolymer shows a much higher thickening capability and a much greater ability to resist shearing, heat, and salts. This good property of the copolymer is attributed to its three-dimensional dimensional network structure. According to the core flooding test, it can be obtained that oil recovery is enhanced about 4.3% by the copolymer flooding contrasted to the HPAM flooding in mid-low permeability cores under conditions of 1500 mg/L of polymers and 45°C. All the results prove that the copolymer has the capability of increasing oil recovery by improving waterflood sweep efficiency in high-salinity reservoirs.     

Effect of amphoteric surfactant on phase behavior of hydrocarbon-electrolyte-water system-an application in enhanced oil recovery

The different techniques such as enhanced oil recovery (EOR) and improved oil recovery (IOR) have been used to enhance oil production. The surfactant flooding is a tertiary oil recovery technique that has been widely used in oil field industry. A variety of surfactant chemicals have been used in which among them the amphoteric type, which has two groups of opposite charges, needs more investigation. In this work, we use cocamidopropyl betaine as an amphoteric surfactant that is used to investigate its influence on the aquifer?+?hydrocarbon system. The effects of surfactant concentration, salinity, and hydrocarbon type on the phase behavior of the various saline aqueous-hydrocarbon mixtures are investigated. Moreover, the surfactant flooding is carried out using a glass micromodel. Thus, to investigate the wettability, the contact angle is also measured for the present system that it is an influential factor in oil recovery. First, by increasing salinity from 0?wt% to 20?wt% in n-hexadecane, the phase change take placed so that a Winsor formation from type I to III and then to type II occurs. However, for n-heptane upon enhancing salinity, Winsor type III is transformed to type II so that hydrocarbon (oil) recovery increases and break through occurs with a delay. By increasing salinity, water solubilization parameter decreases for both hydrocarbon and by enhancing both surfactant concentration and salinity leads to reduce the contact angle. Thus, cocamidopropyl betaine works better for the longer hydrocarbon chain.

In the micromodel flooding test upon formation of Winsor II, the recovery is higher and the break through takes place with a delay. However, for the case of Winsor I, the recovery is lower and the break through occurs earlier. Finally, one can conclude that the low concentration of amphoteric surfactants needs to use that plays an important role in chemical EOR and results a higher recovery in high salinity.     

Parametric analysis of surfactant-aided imbibition in fractured carbonates

Many carbonate oil reservoirs are oil-wet and fractured; waterflood recovery is very low. Dilute surfactant solution injection into the fractures can improve oil production from the matrix by altering the wettability of the rock to a water-wetting state. A 2D, two-phase, multicomponent, finite-volume, fully-implicit numerical simulator calibrated with our laboratory results is used to assess the sensitivity of the process to wettability alteration, IFT reduction, oil viscosity, surfactant diffusivity, matrix block dimensions, and permeability heterogeneity. Capillarity drives the oil production at the early stage, but gravity is the major driving force afterwards. Surfactants which alter the wettability to a water-wet regime give higher recovery rates for higher IFT systems. Surfactants which cannot alter wettability give higher recovery for lower IFT systems. As the wettability alteration increases the rate of oil recovery increases. Recovery rate decreases with permeability significantly for a low tension system, but only mildly for high tension systems. Increasing the block dimensions and increasing oil viscosity decreases the rate of oil recovery and is in accordance with the scaling group for a gravity driven process. Heterogeneous layers in a porous medium can increase or decrease the rate of oil recovery depending on the permeability and the aspect ratio of the matrix block.     

The Synergistic Effect of a Mixed Surfactant (Tween 80 and SDBS) on Wettability Alteration of the Oil Wet Quartz Surface

The synergistic effect of a new combination of Tween 80 and sodium dodecylbenzenesulfonate (SDBS) surfactants has been studied for wettability alteration of a reservoir rock. The contact angle decreased substantially for the aqueous solution of the mixed surfactant on a crude oil aged quartz substrate when compared to water and individual surfactants viz. SDBS and Tween 80. This established synergism between anionic and non-ionic surfactants. The optimal salinity for reduction of the contact angle has been figured out. The rheological effect of the mixed surfactant solution on the wettability alteration has been investigated. Adsorption of crude components at the solid–fluid interfaces has been observed to visualize the activity at the micro scale. Quantification of adsorption for the mixed surfactant on sand has been studied to meet the economical aspect. Reaction aspects of the mixed surfactant–quartz–crude oil system have been interpreted from FTIR. Functional groups present in the system have also been enquired.     

A Modified Contact Angle Measurement Process to Suppress Oil Drop Spreading and Improve Precision

Static contact angle measurement is a widely applied method for wettability assessment. Despite its convenience, it suffers from errors induced by contact angle hysteresis, material heterogeneity, and other factors. This paper discusses the oil drop spreading phenomenon that was frequently observed during contact angle measurements. Experimental tests showed that this phenomenon is closely related to surfactants in the surrounding phase, the remaining oil on the rock surface, and oil inside the surrounding phase. A modified contact angle measurement process was proposed. In the modified method, deionized water was used as the surrounding phase, and a rock surface cleaning step was added. Subsequent measurements showed a very low chance of oil drop spreading and improved precision. A further comparison study showed that, when the surrounding phase was deionized water, the measured contact angle values tended to be closer to intermediate-wet conditions compared to the values measured in clean surfactant solutions. This difference became more significant when the surface was strongly water-wet or strongly oil-wet. As a result, the developed process has two prerequisites: that the in-situ contact angle values inside surfactant solutions are not required, and that the wettability alteration induced by the surfactant solution is irreversible.     

Rheological properties and enhanced oil recovery performance of a novel sulfonate polyacrylamide

A novel hydrosoluble sulfonate copolymer (SPAM) containing sulfonic acid groups was synthesized under mild conditions with Acrylamide (AM), 2-(Dimethylamino) ethyl methacrylate (DMAEMA) and 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propane sulfonic acid (AMPS) as monomers by segmentation initiation with 2,2'-azobis[2-methylpropionamidine] dihydrochloride and redox initiation system, respectively. The structures of copolymers were characterized by infrared (IR) spectroscopy, ¹H NMR spectroscopy and thermogravimetric analysis. The rheological properties of the copolymer solution at different shear rate, temperature and salt concentration were investigated. The shear-tolerance, temperature-tolerance and salt-tolerance of the novel synthetic hydrosoluble sulfonate copolymer are improved remarkably compared with partially hydrolyzed polyacrylamide (HPAM). The synthetic copolymer solution possesses a higher viscosity retention rate (53.3%) than HPAM (35.3%) at the total salinity of 20000 mg/L when temperature changed from 30°C to 99°C. The enhanced oil recovery (EOR) of the synthetic copolymer was performed by core flood, and the EOR degree of the synthetic copolymer in the 20000 mg/L salt solution at 80°C was better than that of HPAM. Compared with HPAM flooding, the EOR with the synthetic copolymer flooding was increased by 6.8% at 80°C.     

Mechanistic study of nanoparticles–surfactant foam flow in etched glass micro-models

This study was conducted in order to identify the pore-level mechanisms controlling the nanoparticles–surfactant foams flow process and residual oil mobilization in etched glass micro-models. The dominant mechanism of foam propagation and residual oil mobilization in water-wet system was identified as lamellae division and emulsification of oil, respectively. There was inter-bubble trapping of oil and water, lamellae detaching and collapsing of SDS-foam in the presence of oil in water-wet system and in oil-wet system. The dominant mechanisms of nanoparticles–surfactant foam flow and residual oil mobilization in oil-wet system were the generation of pore spanning continuous gas foam. The identified mechanisms were independent of pore geometry. The SiO₂-SDS and Al₂O₃-SDS foams propagate successfully in water-wet and oil-wet systems; foam coalescence was prevented during film stretching due to the adsorption and accumulation of the nanoparticles at the gas–liquid interface of the foam, which increased the films’ interfacial viscoelasticity.     

Study of Spontaneous Imbibition of Water by Oil-Wet Sandstone Cores Using Different Surfactants

The mechanism of spontaneous imbibition of water by sandstone cores and the relationship between reservoir wettability and imbibition recovery were studied by investigating factors influencing the spontaneous imbibition of different surfactants by oil-wet sandstone cores. Ultimate oil recovery of cores using the cationic surfactant CTAB was higher than that of the cores using the nonionic surfactant TX-100 and the anionic surfactant POE (1) at the same concentration. For CTAB and TX-100, the ultimate oil recovery by spontaneous imbibition increased with increase in surfactant concentration. In regard to imbibition recovery, TX-100 and POE(1) at high temperatures were superior to those at low temperatures. Ultimate oil recovery of the high-permeability core was higher than that of the low-permeability core at room temperature. According to changes in the driving force during the imbibition process, the imbibition curve could be divided into three regions: (1) mainly capillary force, (2) both capillary and gravity forces, and (3) mainly gravity force. The stronger the hydrophilicity of the rock surface, the higher the spontaneous imbibition recovery.     

Production of Microbial Rhamnolipid by Pseudomonas Aeruginosa MM1011 for Ex Situ Enhanced Oil Recovery

Recently, several investigations have been carried out on the in situ bacteria flooding, but the ex situ biosurfactant production and addition to the sand pack as agents for microbial enhanced oil recovery (MEOR) has little been studied. In order to develop suitable technology for ex situ MEOR processes, it is essential to carry out tests about it. Therefore, this work tries to fill the gap. The intention of this study was to investigate whether the rhamnolipid mix could be produced in high enough quantities for enhanced oil recovery in the laboratory scale and prove its potential use as an effective material for field application. In this work, the ability of Pseudomonas aeruginosa MM1011 to grow and produce rhamnolipid on sunflower as sole carbon source under nitrogen limitation was shown. The production of Rha-C₁₀-C₁₀ and Rha₂-C₁₀-C₁₀ was confirmed by thin-layer chromatography and high-performance liquid chromatography analysis. The rhamnolipid mixture obtained was able to reduce the surface and interfacial tension of water to 26 and 2 mN/m, respectively. The critical micelle concentration was 120 mg/L. Maximum rhamnolipid production reached to about 0.7 g/L in a shake flask. The yield of rhamnolipid per biomass (Y _RL/x ), rhamnolipid per sunflower oil (Y _RL/s ), and the biomass per sunflower oil (Y _x/s ) for shake flask were obtained about 0.01, 0.0035, and 0.035 g g^?1, respectively. The stability of the rhamnolipid at different salinities, pH and temperature, and also, its emulsifying activity has been investigated. It is an effective surfactant at very low concentrations over a wide range of temperatures, pHs, and salt concentrations, and it also has the ability to emulsify oil, which is essential for enhanced oil recovery. With 120 mg/L rhamnolipid, 27 % of original oil in place was recovered after water flooding from a sand pack. This result not only suggests rhamnolipids as appropriate model biosurfactants for MEOR, but it even shows the potential as a biosurfactant of choice for actual MEOR applications.     

Stability of Polymer and Surfactant Mixture Enhanced Foams in the Presence of Oil Under Static and Dynamic Conditions

Three different types of foaming agents including hydrocarbon surfactant TQ01, partial fluorinated surfactant BF01, and per-fluorinated surfactant QF01 exhibited good foaming ability and foam stability under 95°C high temperature and 32,325 ppm salinity conditions. The oil-tolerance ability order with respect to Malaysia Off-shore (MOS) crude oil for surfactant TQ01, BF01, and QF01 is TQ01 < BF01 < QF01. Introduction of polymer into the foam formula could significantly increase foam stability. Different polymers show different abilities of increasing foam stability. Spreading coefficient and entering coefficient are close to zero for surfactant BF01 foaming system and much less than zero for surfactant QF01 foaming system, so the oil-resistance ability of foam generated by surfactant QF01 is the strongest. For surfactant TQ01 foaming system, the calculated spreading coefficient and entering coefficient are greater than zero; therefore, the TQ01 foam system is more sensitive to MOS crude oil and its oil-resistance ability is the poorest. Core flooding test indicated that using the 0.4% BF01 and 0.2% YH1096 combined foaming formula could increase the pressure drop across the porous media significantly, indicating that strong foam was generated in the presence of MOS crude oil.     

Interaction between polymer and anionic/nonionic surfactants and its mechanism of enhanced oil recovery

Various experimental methods were used to investigate interaction between polymer and anionic/nonionic surfactants and mechanisms of enhanced oil recovery by anionic/nonionic surfactants in the present paper. The complex surfactant molecules are adsorbed in the mixed micelles or aggregates formed by the hydrophobic association of hydrophobic groups of polymers, making the surfactant molecules at oil-water interface reduce and the value of interfacial tension between oil and water increase. A dense spatial network structure is formed by the interaction between the mixed aggregates and hydrophobic groups of the polymer molecular chains, making the hydrodynamic volume of the aggregates and the viscosity of the polymer solution increase. Because of the formation of the mixed adsorption layer at oil and water interface by synergistic effect, ultra-low interfacial tension (～2.0?×?10^?3 mN/m) can be achieved between the novel surfactant system and the oil samples in this paper. Because of hydrophobic interaction, wettability alteration of oil-wet surface was induced by the adsorption of the surfactant system on the solid surface. Moreover, the studied surfactant system had a certain degree of spontaneous emulsification ability (D50?=?25.04?µm) and was well emulsified with crude oil after the mechanical oscillation (D50?=?4.27?µm).