Surfactant-based Enhanced Oil Recovery Research Articles

The synergistic effects of cationic surfactant and smart seawater on the recovery of medium-viscosity crude oil from low-permeability carbonates

In the petroleum industry, there is a continuous search for cost-effective enhanced oil recovery (EOR) methods to increase oil extraction. Surfactant-based EOR is one of these effective methods, which is applied after the primary and secondary recovery phases. This paper presents an experimental study on the use of a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB, CH3(CH2)15N(Br)(CH3)3), and smart seawater (SW) for EOR in low-permeability carbonate rock with medium viscosity crude oil. Smart SW was prepared by modifying the concentrations of Ca2+, Mg2+, and SO42- in synthetic offshore SW. The aqueous stability of CTAB was tested in different salinities of smart SW at the reservoir temperature. It was demonstrated that CTAB is stable at 55 °C, which was further confirmed through optical transmittance measurements, revealing values mostly exceeding 93%. The use of smart SW and CTAB significantly altered the wettability of carbonate rock towards water-wet and reduced the interfacial tension (IFT) between crude oil and water, reaching levels below 0.087 mN/m. However, the presence of smart SW increased the adsorption of CTAB onto the surface of carbonate rock. Nevertheless, the adsorption values were significantly below 1 mg/g-rock. Smart SW + CTAB resulted in a total oil recovery of 76.71% of original oil-in-place (OOIP), compared to 71.70% of OOIP with unmodified SW + CTAB. These results suggest that the use of smart SW in combination with CTAB is a promising approach for enhancing the recovery of medium-viscosity oil from tight carbonate reservoirs. Findings from this study can help in better understanding the optimal conditions for the application of smart SW-CTAB flooding to improve the effectiveness of tertiary recovery operations in the upstream oil sector.

New charged aggregate mathematical models to predict the behavior, structural parameters, and geometrical features of microemulsions

Experimental characterization techniques can provide qualitative and quantitative information on the behavior and properties of microemulsion systems. However, they suffer from several inherent drawbacks that often restrict their application to research settings rather than routine practice in various industries. Also, the majority of theoretical studies on microemulsion systems have focused on nonionic surfactants and suffer from restrictive assumptions and limitations that can be violated under realistic conditions. Therefore, their practical applications to real-world problems such as surfactant-based enhanced oil recovery (EOR) processes require the exercise of extreme caution. This work is intended to fill existing research gaps and solve industrial challenges by developing new mathematical models for predicting micelle size besides other structural and geometrical parameters in ionic surfactant-induced oil-in-water (O/W) and water-in-oil (W/O) microemulsions. The main purpose of the present study is to derive novel models that are not only fitting-free, objective, independent of iterative algorithms and experimental data, and inclusive of intermicellar interactions, but also applicable to complex systems containing real crude oil, experiencing compositional changes, and under any thermodynamic conditions. First, a recently proposed surface charging model for dispersions of charged particles in electrolyte solutions is combined with the DLVO theory of colloidal interactions to develop a thermodynamic model for the structural description of O/W microemulsions. Then, upon coupling a surface charging model for non-electrolyte dispersions of charged aqueous cavities with the DLVO theory, another thermodynamic model is developed for W/O microemulsions. Next, the developed mathematical models are supplemented with an auxiliary material balance equation and an equilibrium condition to calculate the radius of micelles in each type of systems. After determining the radii of oil- and water-swollen micelles using the new models, other geometrical and structural parameters such as solubilized phase-to-surfactant molar ratio, aggregation number, the volumes of microemulsion and excess phases, intermicellar distance, and periodicity are readily calculated in an explicit manner using the derived relationships. Afterwards, some reliable complementary tools are discussed for calculations of the associated physical parameters to avoid the need for experimental measurements, thereby making the models more practical and operational. Finally, the validity of the developed models is verified using literature experimental data.

Technology Focus: EOR Modeling (January 2023)

The oil and gas industry is facing unprecedented responsibility and expectations to keep fueling the world’s economies and social developments with reliable, accessible, safe, and affordable energy sources while responding to the global urgency to safeguard natural resources and protect the environment. Most major oil and gas companies have announced decarbonization strategies for low-carbon or net-zero emissions associated with their business operations. Consequently, reducing the carbon intensity of oil production [kilograms of carbon dioxide (CO2) equivalent emitted per produced barrel of oil] will be pivotal to meeting the environmental mandate. On the other hand, approximately 70% of the world’s counties have set targets to reach net zero within the next 3–5 decades, including emissions from burned hydrocarbon, which is a major challenge. Within this exigent mission to transition the industry, a major question arises about the merit and the role of enhanced oil recovery (EOR). With a share below 3% of the global oil production, field-scale EOR deployment and contribution have been modest despite substantial investments made in research and development and piloting in the last 4 decades. This underperformance of EOR has been attributed mostly to competitive alternatives (waterflooding), high cost, complex infrastructure and supply chains, fluctuating oil prices, and others. In the era of thirst for sustainability in our industry, there are reviving opportunities for selective EOR methods that can achieve efficient oil production with low carbon intensity. For instance, CO2 EOR is intuitively a win/win technology. This method may not be feasible everywhere for various reasons, however, including the availability and proximity of CO2 sources and the suitability of reservoir conditions. Chemical EOR methods, such as low-salinity, polymer-, and surfactant-based methods with low chemical usages have the potential to reduce water usage and enhance recovery factors, particularly from tight oil reservoirs. In contrast, EOR methods that are inherently associated with high carbon intensity, such as thermal EOR, will face stricter constraints to perform, including prohibitive costs for carbon offsetting. Advanced modeling and optimization, including guided machine learning and data analytics, will be crucial to maximizing recovery, quantifying uncertainties, and managing risk while preserving resources and reducing costs. The selected papers in this feature include examples of innovative approaches for developing efficient EOR schemes and advanced modeling and optimization. In one inclusion, optimized water chemistry is engineered for various EOR schemes (e.g., polymer, surfactant, CO2) to improve efficiency while reducing chemical usage. The second inclusion demonstrates an integrated core-to-field work flow to design surfactant-based EOR for a tight formation at the laboratory scale and demonstrate its performance using field-scale simulations. An integrated optimization approach for a Permian CO2-EOR field is demonstrated in the third paper, where an advanced Bayesian framework is used to capture uncertainties. Our industry has consistently demonstrated resilience, adaptivity, and creativity. In the era of industry transition to low-carbon operations, opportunities exist for selective EOR methods to revive and contribute. Recommended additional reading at OnePetro: www.onepetro.org. SPE 208121 Polymer Injection To Unlock Bypassed Oil in a Giant Carbonate Reservoir: Bridging the Gap Between Laboratory and Large-Scale Polymer Project by Clement Fabbri, ADNOC, et al. SPE 208127 The World’s First Offshore Gravity-Assisted Simultaneous Water-Alternating-Gas EOR Full-Field Implementation by Ahmad Khanifar, Petronas, et al. SPE 207449 Numerical Optimization of Water-Alternating-Gas Injection in a Sandstone Field Using a Coupled Surface and Subsurface Model by Thaer I. Ismail, Khalifa University of Science and Technology, et al.

Application of Surfactant-based enhanced oil recovery in carbonate Reservoirs: A critical review of the opportunities and challenges

The oil productionfromcarbonate formations is low because of complicatedcompositions, formation heterogeneity, oil-wet/mixed wet conditions, etc. Primary recovery depends on the reservoir's natural resources for production and is often supplemented by secondary recovery methods such as water flooding or immiscible gas injection to generate an artificial drive and complement reservoir energy. Tertiary recovery strategies should be used to mobilize residual oil saturation and increase oil recoveries from these reservoirs using various chemical flooding and chemical agent systems. Polymer flooding, surfactant flooding, alkali flooding, and combinations of these flooding methods are different types of Chemical floodingEOR (C-EOR) technology. Surfactant flooding procedures have been regarded as reliable EOR methodsfor field utilization because they minimize interfacial tensions and modify reservoir rock wetting characteristics, reducedcapillary forces and thus promote oil recovery. This paper provides a review of field projects and large-scale operations of surfactantfloodingin carbonate reservoirs. The fundamentalprocesses of various chemical systems, as well as the interactions of various compoundswith reservoir rocks and fluids, have been examined. After a sequence of assessment steps, the required surfactant flooding for a range of specific reservoir conditions is determined. The properties of a surfactant such as formulation and characteristics of reservoirs such as temperature, salinity, pH, rock permeability, formation type, wettability and other considerations are discussed. Moreover, since carbonate reservoirs are distinguished with a considerableheterogeneity, high temperature, and high salinity conditions, surfactant and polymer choosingfor these kind of reservoirs is a difficult process that requires experimental test to obtain the best quantity and composition of chemicals. Field project design and technical insights can be used to generate innovative strategies that will have a direct effect on the internationaloil supply in the immediate future.

New insights into the mechanism of surfactant enhanced oil recovery: Micellar solubilization and in-situ emulsification

Reducing the oil-water interfacial tension (IFT) to ultra-low is believed the primary mechanism for surfactant-based enhanced oil recovery (EOR) process. However, field trials have shown that low concentration surfactant flooding can also improve oil recovery without ultra-low IFT. To clarify the mechanism behind, the currently-used surfactant, naphthenic arylsulfonate (NAS), was used to unravel its function during surfactant flooding from the horizon of micron- and nano-scale. The solubilization capacity of NAS micelle to petroleum fractions was evaluated through light absorbance strategy, small-angle neutron scattering, dynamic light scattering and transmission electron microscopy. It was found that micellar solubilization plays a significant role during the surfactant flooding. In-situ emulsification was visualized in microfluidics with three types of microchips, respectively. A series of displacement tests were carried out with NAS solution pumping into oil-saturated chip. The results show that in-situ emulsification improve oil recovery mainly through blocking and entrainment effects. Results from this work aid in understanding the interaction between surfactant solution and petroleum fractions at low surfactant concentration, which is helpful for design surfactant-based displacing system for EOR process.

Static Adsorption Evaluation for Anionic-Nonionic Surfactant Mixture on Sandstone in the Presence of Crude Oil at High Reservoir Temperature Condition

Summary The application of surfactants in enhanced oil recovery (EOR) has revealed over the years various challenges that impose limitations on the successful implementation of surfactant flooding. Surfactant adsorption is one of the most important aspects that strongly dictates the feasibility of surfactant-based EOR. The effect of the presence of crude oil on surfactant adsorption and the influence of surfactant partitioning on the adsorption quantification are presented in this paper. Static adsorption experiments were conducted in this study for a surfactant mixture [alkyl ether carboxylate (AEC):alkylpolyglucoside (APG)] on sandstone rock samples in the absence and presence of crude oil. Partitioning experiments were carried out to evaluate the surfactant partitioning between the aqueous surfactant solution and the crude oil to determine the partitioning influence on the adsorption results in the presence of crude oil. The mixture’s adsorption and partitioning behaviors were studied at a fixed salinity of 32 k ppm and temperatures of 80 and 106°C. High-performance liquid chromatography (HPLC) was used in measuring the surfactant concentration throughout adsorption and partitioning tests. Rock characterization was also performed in this study using X-ray diffraction (XRD) as well as X-ray photoelectron spectroscopy (XPS) before and after adsorption with and without crude oil being present. Static adsorption outcomes displayed the adsorption of APG, AEC, and the overall mixture with and without crude oil being present, because all are having a similar increasing trend when concentration increases. However, the adsorption values were much higher when crude oil was present as compared with the adsorption values when crude oil was absent; this is because of not considering the impact of surfactant partitioning. The adsorption values (i.e., at 0.2 wt%) for both temperatures were below 2.5 mg/g in the absence of crude oil and rose to around 3.5 mg/g in the presence of crude oil. A significant amount of what was adsorbed belongs to AEC because of its increased chain-chain interactions with APG, which was evidenced experimentally in our previous work; hence, AEC is the greatest contributor to the overall surfactant mixture’s adsorption. Also, temperature had an impact on the adsorption capacity of the AEC:APG mixture, showing that APG has a greater sensitivity to temperature in comparison to AEC. The adsorption behavior of APG was found to be the opposite of AEC, where the adsorption capacity at 106°C was lower for AEC than its adsorption capacity at 80°C and vice versa for APG. The surfactant partitioning results were used to validate the surfactant adsorption outcomes in the presence of crude oil. After eliminating the partitioning effect, the surfactant adsorption isotherms in both cases of the presence and the absence of crude oil were almost identical. The results highlighted the importance of measuring surfactant partitioning, and the impact that partitioning has on the total surfactant losses during the surfactant flooding process. XRD and XPS results indicated that the change of the rock structure after adsorption when crude oil was present was attributed to the rock dissolution phenomena. It was concluded that adsorption and partitioning take place in the water/oil/rock system simultaneously and taking that into account allows for the improved and proper designing of the surfactant flooding.

Reducing anionic surfactant adsorption using polyacrylate as sacrificial agent investigated by QCM-D

Surfactant losses by adsorption to rock surfaces make surfactant-based enhanced oil recovery economically less feasible. We investigated polyacrylate (PA) as a sacrificial agent in the reduction of anionic surfactant adsorption with focus on calcite surfaces by using quartz crystal microbalance with dissipation monitoring. It was found that the adsorption of the anionic surfactant alcohol alkoxy sulfate (AAS) followed a Langmuir adsorption isotherm, and the adsorbed amount reached saturation above its critical micellar concentration. Adsorption of PA was a much slower process compared to AAS adsorption. Increasing the calcium ion concentration also increased the amount of AAS adsorbed as well as the mass increase rate of PA adsorption. Experimental results combined with density functional theory calculations indicated that calcium cation bridging was important for anionic surfactant AAS and PA adsorption to calcite surfaces. To effectively reduce the amount of surfactant adsorption, it was needed to preflush with PA, rather than by a simultaneous injection. Preflushing with 30 ppm of PA gave a reduction of AAS adsorption of 30% under high salinity (HS, 31,800 ppm) conditions, compared to 8% reduction under low salinity (LS, 3180 ppm) conditions. In the absence of PA, the amount of adsorbed AAS was reduced by already 50% upon changing from HS to LS conditions. Lower calcium ion concentrations, as under LS conditions, contributed to this observation. On different mineral surfaces, PA reduced the AAS adsorption in the order of alumina > calcite > silica. These results offer important insights into mitigating surfactant adsorption using PA polyelectrolyte as sacrificial agent and contribute to improved flooding strategies with reduced surfactant loss.

Partitioning behaviour of novel surfactant mixture for high reservoir temperature and high salinity conditions

Investigating the use of surfactants in high temperature and high salinity conditions can assist expanding the application of surfactant-based enhanced oil recovery (EOR) to more challenging environments. In the present work, compatibility and thermal stability for alkyl ether carboxylate (AEC) and alkylpolyglucoside (APG) were investigated at anaerobic conditions. The most suitable surfactant formulation was selected after passing the screening criteria of compatibility and thermal stability for the studied offshore field. Interfacial tension (IFT) and partitioning of the selected surfactant formulation were then studied at different surfactant concentrations, brine/oil ratios, temperatures, and salinities. The partitioning behaviour of the AEC:APG mixture was comprehensively examined under the before mentioned conditions. The screening experiments for the individual surfactant AEC have shown poor compatibility and thermal stability. Whereas, a 50:50 ratio of the anionic-nonionic (AEC:APG) mixture has passed the compatibility test criteria. For 90 days, the mixture demonstrated remarkable compatibility and thermal stability at high water salinity (32k ppm) and high temperature (106 °C). The IFT of the AEC:APG mixture was significantly affected by the increase of surfactant concentration, temperature and salinity. The proposed mechanism, through the experimental results, illustrated that as surfactant mixture concentration gradually increased, additional molecules of AEC occupied the interface whereas the APG molecules tend to attach to the existed APG molecules at the interface via hydrogen bonds and they both formed a new interface. The formed interface caused the increment of the IFT values. The outcomes proved that APG was the most dominant surfactant as it had the highest impact on the mixture behaviour. It is believed that the outcomes of this work are expected to provide a better fundamental understanding of the surfactant partitioning behaviour in high temperature and high salinity conditions, as well as providing a basic guideline to design efficient surfactant flooding slugs.

Experimental and numerical study of surfactant solution spontaneous imbibition in shale oil reservoirs

Abstract Experimental and simulation studies have thus far demonstrated that surfactant-based Enhanced Oil Recovery (EOR) is a feasible method to improve recoveries from initially oil-wet or mixed-wet Unconventional Oil Reservoirs (UORs). The summarized principle is that surfactant triggers spontaneous imbibition by either Interfacial Tension (IFT) reduction or wettability alteration. Several related studies have focused on the effectiveness of different surfactants or their combinations on the final oil recoveries from selected rock/fluid samples. However, the relative significance of each mechanism is not clear yet. In this work, by following both experimental and numerical simulation approach, we attempt to separately investigate the effect of IFT reduction and wettability alteration on the performance of surfactant based EOR in UORs. Further, the relative importance of each function is addressed while determining the dominating mechanism. Both experimental and simulation results showed that achieving a water-wet status is crucial for higher oil recoveries in shale and tight reservoirs. The effects of IFT reduction could be detrimental to the recovery once the wettability is altered to water-wet due to a lower capillary driven force. Therefore, to design a successful surfactant EOR case in UORs, a surfactant must have the capability of altering the wetness to a more water-wet status. Meanwhile, maintaining a relatively high IFT is also significant. Results from this paper will provide a general suggestion on surfactant selection to enhance oil recovery in UORs.

Adsorption of natural surfactants on sandstone rocks: Effect on the quality of the recovered asphaltenic oil

ABSTRACTNatural surfactants are important for any enhancing oil recovery applications since these kinds of surfactants have less detrimental effects and also lower cost in comparison to the industrial surfactants. Adsorption of surfactants on sandstone minerals is an important issue which needs to be considered before applying any surfactant-based enhanced oil recovery technique. In this study, a new model based on adaptive neuro-fuzzy interference system was developed in order to simulate the kinetic behavior of natural surfactants adsorption on sandstone minerals with high accuracy. Performance of the model was investigated by comparing the results of the proposed model with the results of previous well-known kinetic models. Results demonstrated that this model has the highest accuracy compared to the other well-established models found in literature. Finally, in order to show the importance of modeling surfactants adsorption, the effect of a natural surfactant on the quality of the produced oil was investigated by performing SARA analysis on the recovered oil at various conditions of surfactant adsorption. It is shown that in the case of lower surfactant adsorption on sandstone minerals, the produced oil has higher asphaltene fractions.

Surface tension behavior of aqueous solutions of a propoxylated surfactant and interfacial tension behavior against a crude oil

Equilibrium interfacial tensions (EIFTs) are important in determining the oil recovery efficiency in surfactant-based enhanced oil recovery (EOR) processes, in which ultralow IFT values (less than 10−2mNm−1) are often needed. The dynamic IFTs (DIFTs) for un-pre-equilibrated drops in contact with aqueous solutions and the adsorption mechanisms at the oil-water interface are important for the initial stages of EOR and for screening various surfactants for field applications. The IFT behavior of a commercial anionic surfactant, termed S13D, a single-chain propoxylated sodium sulfate salt has been studied. The synthetic brine used (9700ppm total dissolved solids) was similar to that in an actual reservoir of oil, from which purified crude oil samples were prepared.The dynamic and equilibrium surface tensions (DSTs and ESTs) and the IFTs were measured at 24°C, with the emerging bubble/drop method, or the spinning bubble/drop method. The DSTs for surfactant concentrations from 0.1 to 10,000ppm by weight have a simpler adsorption mechanism than the DIFTs, involving only diffusion from the aqueous phase and adsorption/desorption. Surface and interfacial tension relaxation tests after surface area perturbation were performed for establishing the validity of the ESTs and EIFTs. The critical micelle concentration (cmc) was 12ppm in water and 1ppm in brine. The lowest observed EIFT was 1mNm−1 with water and ultralow, 2×10−3mNm−1, with brine. The equilibration timescales were shorter with brine than with water, for both DSTs and DIFTs, and slightly longer for DIFTs, because evidently the adsorbed surfactant desorbed and diffused away from the interface, for partitioning in the oil phase. The results suggest that the IFTs were associated with the typical adsorbed soluble monolayers at the oil-water interface, and that solubilization effects did not affect the measured DIFTs and EIFTs.

Static Adsorption and Retention of Viscoelastic Surfactant in Porous Media: EOR Implication

The mass loss of surfactant during flowing through porous media is one of the major concerns to surfactant-based Enhanced Oil Recovery (EOR) techniques and also a critical issue for viscoelastic surfactant (VES), which is a novel and promising flooding agent compared against the traditional displacing chemicals. This paper comprehensively investigated the interactions between a VES and several minerals. The static adsorption tests of VES on quartz, montmorillonite and kaolinite were first carried out at 65 °C. Empirical models were established to describe the VES adsorptive isothermal beahviors on the mineral surfaces. The data indicated that the VES showed L, S and LS adsorption isotherm patterns on quartz, montmorillonite, and kaolinite, respectively. The adsorption of VES was notably influenced by temperature, pH value, salinity and Ca2+. As a result of adsorption on clay surfaces, the viscosity and surface activity of the VES solution were significantly decreased. Moreover, the large hydrodynamic size...

The Wettability Alteration and the Effect of Initial Rock Wettability on Oil Recovery in Surfactant-based Enhanced Oil Recovery Processes

Wettablity alteration of rock surface is an important mechanism for surfactant-based enhanced oil recovery (EOR) processes. Two salt and temperature-tolerant surfactant formulations were developed based on the conditions of high temperature (97–120°C) and high salinity (20 × 104 mg/L) reservoirs where a surfactant-based EOR process is attempted. Both the two sufactant formulations can achieve ultralow interfacial tension level (≤10−3 mN/m) with crude oil after aging for 125 days at reservoir conditions. Wettability alteration of core slices induced by the two surfactant formulations was evalutated by measuring contact angles. Core flooding experiments were carried out to study the influence of initial rock wettabilities on oil recovery in the crude oil/surfactant/formation water/rock system. The results indicated that the two formulations could turn oil-wet core slices into water-wet at 90–120°C and 20 × 104 mg/L salinity, while the water-wet core slices retained their hydrophilic nature. The core flooding experiments showed that the water-wet cores could yield higher oil recovery compared with the oil-wet cores in water flooding, surfactant, and subsequent water flooding process. The two surfactant formulations could successfully yield additional oil recovery in both oil-wet and water-wet cores.

Reducing adsorption of anionic surfactant for enhanced oil recovery: Part II. Applied aspects

The surfactant loss due to adsorption has significant economic consequences for surfactant-based enhanced oil recovery (EOR) processes. Alkali, traditionally used as sacrificial agent to reduce adsorption of anionic surfactants, cannot be efficiently used in the presence of anhydrite due to the reactivity of carbonate with anhydrite. In our previous publication, the competitive adsorption mechanism of an anionic surfactant and polyacrylate has been studied. In this work, the effect of some reservoir parameters on application of polyacrylate as a sacrificial agent is investigated. Addition of polyacrylate is shown to reduce adsorption of different anionic surfactants on different outcrop minerals, including Carlpool dolomite, industrial calcite, kaolinite, Berea sandstone, and Indiana limestone. The effect of salinity, concentration of Ca2+ ions, and temperature on effectiveness of sodium polyacrylate as sacrificial agent has been evaluated on different minerals/rocks. Results of dynamic adsorption measurements with sodium polyacrylate are also reported. Cost analysis shows that addition of a small amount of polyacrylate can significantly decrease the total material cost to as low as one-fifth of that without use of sacrificial agent. The reduction in cost depends on the values of dimensionless numbers developed in this paper. Altogether, these experiments demonstrate the advantage of using sodium polyacrylate as sacrificial adsorption agent for anionic surfactants even in the presence of anhydrite in the reservoir.

Pore-scale flow characterization of low-interfacial tension flow through mixed-wet porous media with different pore geometries

The low-interfacial tension flow through porous media occurs in surfactant-based enhanced oil recovery (EOR), soil clean-up, underground removal of the non-aqueous phase liquid and dense non-aqueous phase liquid, etc. In surfactant-based EOR processes, numerous works have been carried out to characterize – either qualitatively or quantitatively – the micro- and macro-scale flow behavior. What has been lacking is to link the statistics of oil blobs population (e.g., distribution of blob length and diameter) to the pore-scale phenomena and macro-scale quantities. In particular, no work has been reported to elucidate the effect of the ratio of pore body to throat diameter (i.e., aspect ratio) on the pore-scale characterization based on the blobs population statistics. The significance of the aspect ratio lies in that it describes the geometry of a porous medium and is one of the foremost morphological features. The aspect ratio is also one of the fundamental factors governing the pore-level events. This study presents the effect of aspect ratio on the statistical distribution of the blob length and equivalent diameter and links the blobs population statistics to the observed pore-level events. The pore-scale variation of the ratio of viscous-to-capillary forces acted on the oil blobs at the threshold of displacement is utilized to characterize the effect of blob length distribution at different aspect ratios. It also provides some insight into correlating the change in oil recovery efficiency and capillary number, by change in aspect ratio, with the change in blobs population statistics.

Insight into the Chemistry of Surfactant-Based Enhanced Oil Recovery Processes

Insight into the Chemistry of Surfactant-Based Enhanced Oil Recovery Processes

Insight into the Chemistry of Surfactant-Based Enhanced Oil Recovery Processes

During the past several decades, significant and considerable research has been carried out on secondary and tertiary recovery of trapped residual oil remaining within the producing formations underground despite the efficient, current primary production strategies and methods. Methods have been sought of increasing oil recovery, while revamping and improving the economic viability and efficiency of operations. One method that has received much attention and intensive study over these past decades is the use of surfactant-based chemical flooding. Initial patents and laboratory tests have shown conclusively that chemical solutions and slugs including surfactants, remove considerable oil from the porous medium normally trapped after initial waterflooding. Oil recovery processes by means of surfactant micellar solutions or microemulsions have included the injection of slugs of varied compositions. Patents on surfactant-based enhanced oil recovery processes (such as dilute surfactant flooding, surfactant/polymer flooding, and alkaline/surfactant/polymer flooding) have been issued, starting from the 1920s and particularly after the 1960s, when the technology was put on a scientific basis. These patents were generally concerned with the chemistry of surfactant-based enhanced oil recovery processes including envisioning the use of chemical solutions (slugs) to decrease the surface tension between oil and the flooding medium, screening of surfactants for oil recovery efficiency, chemical (surfactant) slug designs and formulation to mobilize residual oil, documenting petroleum sulfonates useful in surfactant flooding, and other important factors in the chemistry of surfactant-based chemical flooding processes. Moreover, evaluation and determination of optimum chemical systems (slugs) for the best economics for a specific field application have been disclosed and documented in several large oil companies patents in the surfactant-polymer area. In this article, a full-fledged review of the patents on different aspects of the chemistry of surfactant-based enhanced oil recovery processes is presented. Keywords: Surfactant, enhanced oil recovery, chemistry, chemical slug, patent