Alkali-surfactant-polymer Flooding Research Articles

Evaluation of the Oil Recovery Potential and Cost Implication Analysis of Alternative ASP Formulations for Sandstone and Carbonate Reservoirs.

This study explores alternative chemical agents to enhance oil recovery in sandstone and carbonate reservoirs, aiming to address limitations in alkali-surfactant-polymer (ASP) flooding. Existing ASP methods face technical and environmental challenges, prompting research into alternative chemical agents. However, there are limited field deployments of these alternative chemical agents due to high costs, and ternary combinations of these agents remain unexplored. The study investigates a combination of organic alkali, amino acid-based surfactant/surface-active ionic liquid, and biopolymer. Comparative analysis with conventional ASP formulations reveals promising results. Organic alkali and biopolymer combination mitigates the adverse effects of inorganic alkalis on partially hydrolyzed polyacrylamide, enhancing the oil recovery potential. A unit technical cost (UTC) calculation showed that despite higher chemical costs per incremental barrel of oil, the alternative ASP formulations demonstrate comparable costs due to reduced facility cost. Cost-effectiveness will improve with incorporation of factors such as environmental friendliness and reduced preflush requirements. Mass production of these agents could further enhance the economic feasibility. Therefore, this study reveals that careful cost-benefit analysis, the development of low-concentration formulations, and mass production of these chemical agents could facilitate the implementation of these alternatives, ensuring compliance with environmental regulations and enabling ASP flooding in challenging reservoir conditions.

Wear analysis and life prediction of sucker rod and tubing under ternary emulsion lubrication in Daqing oilfield: a case study in block H

Daqing Oilfield as the world’s largest application area of alkali–surfactant–polymer (ASP) flooding, in recent years, with the increase in aging wells, the eccentric wear and deformation of sucker rod and pipe during oil production has become more and more serious. In order to study the effect of emulsion lubrication in ternary composite flooding on eccentric wear of sucker rod and tubing, this paper establishes a calculation model for the depth of tubing wear under different emulsion lubrication conditions through indoor friction and wear experiments combined with White and Dawson wear efficiency theory. Based on this, the finite element method is used to predict the safe wear life of tubing under different component emulsion lubrication. The results show that compared to intact oil pipes, the residual internal pressure strength of oil pipes with defects decreases, and stress concentration occurs at the edges and middle of the defects. The wear life of oil pipes decreases with the increase in pump depth and wear coefficient under emulsion lubrication. The water content and alkali concentration have the most significant effects on the wear life of oil pipes under emulsion lubrication conditions. The safe wear life of sucker rod pipes under emulsion lubrication with a water content of 75% will be increased by 37.8% compared to those in emulsion lubrication with a water content of 95%, and under emulsion lubrication with an alkali concentration of 500 mg/l, the safe wear life will be increased by 50.6% compared to those in emulsion lubrication with a concentration of 2000 mg/l. The research results can provide theoretical and technical support for oilfield enterprises to reduce rod and pipe wear in ASP flooding oil wells, improve the pump inspection cycle of pumping wells, and ensure the safety of oil well work.

Modifications of petroleum industry effluent treatment Method: An approach for quality improvement of process water for ASP flooding and chemical EOR

Several Alkali Surfactant Polymer (ASP) pilot facilities are currently being put into operation across India. The physicochemical parameters of the process water play an important role in the success of ASP flood to improve the recovery. In the current study treated effluent from an effluent treatment plant (ETP) is used as process water for the ASP pilot. The ETP sample water collected shows a lack of improvement in quality in terms of iron content, higher total suspends solids (TSS), high turbidity, and low filterability. The process water has calcium (as Ca + ) 60 mg/L and magnesium (as Mg2 + ) 33 mg/L. These ions are critical in the ASP designing process. The increase in the rate of filtration was determined by plotting the rate of filtration against the cumulative volume (Cerini filtration). The MTSN values were observed to be −1.35 and −1.09. The RPI values are 7.15 and 2.60 at two different time periods. The sample collected showed a lack of improvement in quality. This tube well water after filtration was best suited for ASP flooding. However, the high concentration of calcium results in the formation of calcium carbonate in addition to sodium carbonate (to be used as alkali for ASP). Hence calcium should be removed by softening the process water in the softening plant. The water was treated in the laboratory with a calculated amount of sodium carbonate to remove calcium and magnesium. Which comes out to be 0.30 gm/l of water. After treatment water was filtered and calcium and magnesium concentrations were determined. The calcium concentration was calculated 13 mg/l as compared to 60 mg/l in treated water.

Dose optimization of oil field produced water and advanced water treatment for heavy viscous oil

The treatment and disposal of oil field-produced water from pay zones presents a variety of issues for the hydrocarbon industry. Significant laboratory experimentation is carried out in this research program to design optimized dosages of oil field chemicals to design a water treatment plant for a thin stacked reservoir containing heavy viscous oil. When produced water is produced by pay zones containing heavy viscous oil, treatment can be difficult. For a better understanding of treatment procedures, chemical properties and physical properties of produced water are analysed. For re-injection of producing water to maintain reservoir pressure, the produced water must be compatible with the rheology of the reservoir under study. If the water leaving oil fields is untreated, it creates problems with injectivity loss and formation degradation, contaminating local groundwater resources and causing a significant environmental disaster. When significant amounts of oil field water is generated, the cost of water treatment chemicals rises dramatically. As a result, after examining the ionic concentration of generated water, this research effort recommends optimizingchemical dosing. Various filtration tests for effective rock fluid compatibility, include series, care, and coarse. The entire water treatment system was designed on prescribed treatment chemical dosages. The primary phase of generated water purification in this study relies heavily on the water treatment technologies of coagulation and flocculation. This processed oil field-producedwater is ideal for Enhanced Oil Recovery such as Alkali Surfactant-Polymer flooding.

A Review of the Seepage Mechanisms of Heavy Oil Emulsions during Chemical Flooding

Chemical flooding plays an important role in enhancing oil recovery due to many reasons, including the viscosity-increment effect of polymer, wettability alteration effect of surfactant, and the formation of emulsions, which have been known to effectively increase the swept area and oil displacement efficiency, hence increasing heavy oil recovery. Laboratory tests and pilot trials of alkali–surfactant–polymer (ASP) injection show that the oil recovery of the emulsified system is 5% more than the cases where no emulsions existed. Therefore, it is of great significance to study heavy oil emulsions and its field application for enhanced heavy oil recovery. This paper discusses a thorough overview of the most fundamental ASP flooding mechanisms, along with some examples of laboratory experiments and field trials. In addition, the formation conditions and the interfacial characteristics of heavy oil emulsions are also discussed, mainly ASP flooding, and then the seepage mechanisms of these emulsions are investigated. The relationship between the formation of heavy oil emulsions and the enhanced heavy oil recovery effect by chemical flooding is discussed through core flooding experiments at the reservoir temperature and some field pilots to reach the optimum heavy oil recovery.

Investigating the generation of ferrous sulfide nanoparticles in the produced fluid after acidizing oil wells and its influence on emulsifying stability between oil and water

Studies show that after acidizing operation of oil wells using the alkali/surfactant/polymer (ASP) flooding technology, the produced fluid is emulsified. Since the produced emulsion is stable, it affects the oil–water separation performance. In order to analyze the generation of stable emulsion in the produced fluid after acidizing an oil well, innovative separation experiments were carried out on real oil wells. During the experiments, solid particles in the middle layer of the emulsifying system in the produced fluid after acidizing ASP flooding were extracted and characterized. The generation of the stable emulsifying system in the produced fluid was studied through stability experiments and molecular dynamics simulations. The results showed that the synergistic effect of ferrous sulfide nanoparticles and surfactants was the fundamental reason for the strong emulsifying stability of the produced liquid after acidizing of the ternary composite system. The generation of ferrous sulfide solid particles mainly included two steps. First, sulfate reducing bacteria in injected water by ASP flooding reacted with sulfate in formation water to form hydrogen sulfide. Then, the hydrogen sulfide reacted with iron metal in oil wells and casing of wellbore to form ferrous sulfide particles. It was found that surfactants are adsorbed on the surface of ferrous sulfide nanoparticles. Subsequently, the control ability of surfactant on oil and water phases in the liquid film was enhanced. The performed analyses demonstrate that the adsorption of solid particles to the oil phase was enhanced, while the free motion of molecules in the oil phase at the liquid film position was weakened. The strength of the interfacial film between oil and water was further increased by the synergistic effect of ferrous sulfide nanoparticles and surfactant. The present study is expected to provide a guideline for a better understanding of the efficient treatment of produced fluids in ASP flooding.

Application of Polymers for Chemical Enhanced Oil Recovery: A Review.

Polymers play a significant role in enhanced oil recovery (EOR) due to their viscoelastic properties and macromolecular structure. Herein, the mechanisms of the application of polymeric materials for enhanced oil recovery are elucidated. Subsequently, the polymer types used for EOR, namely synthetic polymers and natural polymers (biopolymers), and their properties are discussed. Moreover, the numerous applications for EOR such as polymer flooding, polymer foam flooding, alkali–polymer flooding, surfactant–polymer flooding, alkali–surfactant–polymer flooding, and polymeric nanofluid flooding are appraised and evaluated. Most of the polymers exhibit pseudoplastic behavior in the presence of shear forces. The biopolymers exhibit better salt tolerance and thermal stability but are susceptible to plugging and biodegradation. As for associative synthetic polyacrylamide, several complexities are involved in unlocking its full potential. Hence, hydrolyzed polyacrylamide remains the most coveted polymer for field application of polymer floods. Finally, alkali–surfactant–polymer flooding shows good efficiency at pilot and field scales, while a recently devised polymeric nanofluid shows good potential for field application of polymer flooding for EOR.

Evaluation of the Factors Influencing Residual Oil Evolution after Alkali/Surfactant/Polymer Flooding in Daqing Oilfield

The alkali/surfactant/polymer (ASP) flood has long been considered to reduce residual oil saturation significantly after waterflood. This paper provides an experimental investigation of the factors (permeability, pore structure, ASP formula, injection volume, viscosity, and injection volume) that influence the evolution of residual oil after ASP flooding. ASP flood experiments were conducted on the cores drilled in Daqing field, and two-dimensional real-structure micromodels were constructed based on these cores. For the ASP core flood experiments, X-ray computed tomography imaging was used for the visualization of the residual oil evolution. For the ASP micromodel flood experiments, images of the residual oil distribution were obtained using a microscope with a 5× magnification objective. The results showed that as water saturation increased during the flood, the proportion of oil clusters decreased, and the proportion of oil droplets first increased and then decreased. For the cores with smaller pore throats and more complex pore structure, the residual oil became more scattered. In this case, the oil clusters became smaller, and oil droplets became easier to retain. An increased injection rate improved the emulsification, resulting in more residual oil in small pores getting replaced. Increasing the viscosity by increasing the polymer concentration improved the sweep efficiency, mainly because residual oil in large pore throats was displaced, but had a negative impact on emulsification. Increasing the viscosity of the injection fluid was shown to have a negative impact on improving the oil recovery ratio, because the mobilization of residual oil in smaller pores was greatly impacted by emulsification. The effect of increasing injection volume on improving recovery was more pronounced for cores with lower permeability.

A review of polymer flooding for enhanced oil recovery

Oil has a significant role as the principal source of energy in a society with rising energy demand. According to the annual report 2021 by Shelf Drilling (a leading provider of jack-up contract drilling services), the world oil consumption grew by 0.8 million barrels per day to reach almost 101 million barrels per day in the year 2019. Several other reports mention that the global crude oil output increased by 2.1 million barrels per day, or 2.3 percent, which is more than three times the global consumption. Additionally, the recent dramatic drop in oil prices compelled oil corporations to reconsider their production plans and cut costs in light of the dynamic oil price environment. While new oil sources are still being discovered and developed, enhanced oil recovery (EOR) methods are being used more frequently. In this review paper, the features of polymers utilized for EOR, including synthetic and natural polymers (biopolymers) are discussed. Also, the numerous EOR applications such as polymer flooding, polymer foam flooding, alkali–polymer flooding, surfactant–polymer flooding, alkali–surfactant polymer flooding, and polymeric nanofluid flooding are generalized and evaluated. With new advancements in the applications of polymeric nanofluid, it is capable of taking over the oil industry efficiently in polymer flooding for EOR. Additionally, due to their general macromolecular structure and viscoelastic characteristics, polymers are important in EOR.

Pore-scale experiments on the synergistic EOR mechanisms between the main components of LASP (lipopeptide-alkali-surfactant-polymer) system

To improve the oil recovery efficiency of ASP (alkali-surfactant-polymer) flooding, lipopeptide surfactant was added into ASP to form a new system (LASP). Core flooding experiments and field pilots suggested that LASP can achieve better oil recovery with lower costs. To determine the synergistic effects of the LASP system, a series of pore-scale flooding experiments were performed to quantify the displacement and sweep efficiencies of the LASP system and its main components independently. The results suggested that the petroleum sulfonate tends to improve displacement efficiency (by 21.1%) and the polymer tends to widen the effective sweep area (by 14.2%). While lipopeptide improved both oil displacement efficiency (31.2%) and sweep efficiency (10.2%) depending on the oil emulsification. Their mixture, that is; LASP, reached a higher displacement (42.1%) and sweep efficiency (12.9%) that depended on synergistic effects between the components. For instance, the bio- and chemical surfactants and the polymer synergistically improved the stability and deformability of oil emulsion, which reduce flow resistance and then improve displacement efficiency. However, the throat-blocking mechanism, which expanded sweep area during lipopeptide flooding, no longer existed in the LASP system. Nevertheless, the LASP system can depend on high viscosity of polymer to effectively expand sweep area. Oil recovery in the LASP system is more than the sum of the mechanism of each component.

An Improved Particle Swarm Optimization algorithm for Optimal Control of ASP Flooding

An optimization for injection of alkali/surfactant/polymer (ASP) flooding in oil recovery is considered in this paper. This optimal control problem (OCP) is formulated as a parameter identification system, where the objective function is revenue maximization and the governing equation is multiphase flow in porous media. We use the ASP concentrations and slug size as the control and give the pointwise constraint for the control. An improved particle swarm optimization (IPSO) which is a particle swarm optimization (PSO) with second-order oscillatory in velocity, is applied to solve the OCP. Finally, an example of the OCP for ASP flooding is exposed and the results show that the IPSO method is effective and feasible.

Combination of alkali–surfactant–polymer​ flooding and horizontal wells to maximize the oil recovery for high water cut oil reservoir

Alkali/surfactant/polymer (ASP) combines the advantages of each of the chemical in the blend. ASP has shown to be an effective and practical method to enhance oil recovery. Compared with vertical wells, fluid flooding by using horizontal wells is believed to be infeasible due to easier fluid breakthrough and subsequent low sweeping efficiency. However, good responses observed in field applications (Daqing oil field, China) show the promising future of ASP flooding using horizontal wells. In this study, a combination of laboratory-scale core displacement experiments and reservoir-scale numerical simulations was used to study the performances of ASP flooding by using horizontal injection/production wells and vertical injection/production wells to reveal the mechanisms responsible for the favorable responses observed in the field. Firstly, displacement experiments in evaluation of ASP flooding using vertical wells and horizontal wells were conducted. The effects of well type on ASP flooding performances were further evaluated by numerical simulation based on a realistic reservoir. The results show that, horizontal well injection/production pattern facilitates a better oil displacement performance due to the higher sweeping volume. This is because horizontal injection/production pattern weakens both the effects of surface heterogeneity and vertical inter-layer heterogeneity during ASP flooding performance. Although horizontal injection/production well pattern is not suitable for water flooding due to the higher chances for water breakthrough, the profile-control characteristic of ASP system blocks the high permeable channels to some extent, providing a better performance in combination with horizontal injection/production well pattern. This work systematically studied the effects of well type on ASP flooding performance at core scale and reservoir scale, and it provides theoretical and practical implications for the application of ASP flooding in enhancing oil recovery for high water cut reservoirs.

Integrated spatiotemporal modeling and mixed-integer approximate dynamic programming for ASP flooding

Alkali–surfactant–polymer (ASP) flooding holds a critical position in oil development. This paper is concerned with the distributed parameter system (DPS) modeling and development scheme optimization of ASP flooding. Owing to the neglect of coupling among three-dimensional (3-D) spatial information, most of the existing data-driven modeling methods fail to provide a high-precision model for this type of strongly nonlinear and spatiotemporal coupling 3-D DPS. To overcome this shortcoming, an integrated spatiotemporal modeling method (ISM) is proposed, which reconstructs temporal–spatial relationship to avoid spatial mapping distortion based on canonical polyadic decomposition (CPD), and a spatiotemporal MSSO-LS-SVM algorithm is presented to compensate the nonlinear dynamics and decrease truncation error. Moreover, the synchronous optimization of ASP injection strategy and oil wells switching scheduling is an urgent industry requirement of intelligent oilfield decision system, which can be described a mixed-integer optimal control/dynamic programming problem. This paper first puts forward a mixed-integer approximate dynamic programming (MIADP) algorithm, dedicated for solving this class of optimal control problem with integer control subset requirements. In the MIADP, a parallel mixed-integer policy improvement framework is developed, where (i) the continuous control weight updates by the temporal difference (TD) error, (ii) the quantum evolution mechanism is designed to learn the integer control, and (iii) the two parts share information interactively and iterate to approach the optimal mixed-integer policy. At last, a case study on ASP flooding is taken, and the superior performance metrics illustrate the effectiveness of the proposed ISM method and MIADP algorithm.

Stability Dynamic Characteristic of Oil-in-Water Emulsion from Alkali-Surfactant-Polymer Flooding.

The relationship model between the droplet lifetime and interface properties is established to characterize the stability of oil droplets, and then, the influence of the alkali–surfactant–polymer (ASP) concentration on the lifetime is analyzed by theoretical calculations. The stability dynamic characteristics of oil-in-water (O/W) emulsions from ASP flooding were evaluated using the emulsion stability model (Civan model) based on two-phase separation. The effect of ASP on dynamic characteristics of the emulsion was explored by analyzing film strength qualitatively and measuring interfacial tension and ζ potential. The results showed that the Civan model was suitable to evaluate the stability of the O/W emulsion and to obtain the corresponding dynamic characteristics. The O/W emulsions became more stable with the increasing alkali concentration first at a low alkali concentration (cNaOH < 200 mg/L) and then became less stable with the increasing alkali concentration at a high alkali concentration (cNaOH > 200 mg/L). The stabilities of O/W emulsions were improved with the increasing concentrations of the surfactant and polymer. The mechanism of stabilization of the O/W emulsion by ASP is as follows. The surface-active substances formed by the reaction of alkali and acidic substances in the oil phase, together with surfactants, adsorb at the oil–water interface, reducing the interfacial tension and increasing the strength of the oil–water interface film. The polymer only increases the strength of the interface film by increasing the viscoelasticity of the oil–water interface film.

Effects of pollutants in alkali/surfactant/polymer (ASP) flooding oilfield wastewater on membrane fouling in direct contact membrane distillation by response surface methodology

The characteristic pollutants in alkali/surfactant/polymer (ASP) flooding oilfield wastewater are complex [e.g., NaCl, sodium dodecyl sulfate (SDS), petroleum, and polyacrylamide (PAM)]; thus, membrane distillation (MD) applied to treat this wastewater will be fouled and wetted easily. In this study, response surface methodology (RSM) was used to analyze the effects of pollutant interactions in ASP flooding oilfield wastewater on membrane fouling. The response model showed quantitative relationships between the membrane flux and the pollutant concentrations. The analysis of variance (p-value of the model < 0.0001, p-value of lack of fit > 0.05, R2 = 0.9750 and R2adj = 0.9500) showed that the regression equation fit the empirical data well. The results also indicated that the interactions of pollutants (NaCl and SDS; petroleum and PAM) had significant influence on the flux decline in the simulated ASP flooding oilfield wastewater. The characterization of Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) revealed that the MD membrane was fouled by simulated ASP flooding oilfield wastewater to a certain degree. Moreover, the membrane flux was restored to 86.9% after hydraulic cleaning.

A comprehensive techno-economic assessment of alkali–surfactant–polymer flooding processes using data-driven approaches

The objective of this work is to propose a machine-learning assisted multi-objective optimization protocol to design and optimize alkali–surfactant–polymer flooding processes in the presence of multiple technical and economic objective functions. Several universal multi-layer neural networks are trained, and they act as universal surrogate models of high-fidelity numerical simulator to evaluate the objective functions involved in the optimization workflow. The HLD-NAC equation is employed to model the microemulsion phase behavior of the crude oil/brine/surfactant system with the presence of alkali agents. The validity of the expert systems is confirmed via extensive blind testing applications with error margins of 9%, which includes the predictions of fluid production and pressure responses. A multi-objective optimization workflow is structured by coupling the expert systems with particle swarm optimizer, which employs Pareto optimum theory to carry comprehensive ASP injection assessments considering various technical and economic objective functions. Moreover, the proposed workflow enables the decision makers to comprehend the project risks by taking the inherent uncertainties from crude oil market into accounts. The robustness of the optimization protocol is verified by introducing a synthetic field case study, which validates the competence of optimizing ASP injection design considering project net present value as an objective function. A series of Pareto front solutions are generated when more objective functions such as chemical efficacies and water cut reductions are included. Subsequently, the workflow evaluates the project economic uncertainties from the fluctuation of oil price, which helps the decision makers investigate the project risks from technical and economic perspectives.

Study on stability of produced water in ASP flooding based on critical micellar theory

The basic properties of produced water and the effect of oil displacement agent for its stability were obtained, through measuring and analyzing water quality characteristics, relationship between critical micelle concentration-oil displacement agent, temperature, pH and content of inorganic salt, particle size distribution and morphology of Nan4-8 and Sanyuan-6 alkali-surfactant-polymer (ASP) produced water of Daqing Oilfield. The critical micelle concentration of ASP flooding was less than its own concentration, and the double bilayer was formed in system. Critical micelle concentration of ASP produced water was less affected by the system temperature and greatly affected by pH. Polymer increases viscosity of produced water and has the properties of surfactant, which partially hydrolyzes under the action of alkali to form polyelectrolyte and promotes the formation of double electric layer. Therefore, the coalescence of oil droplets in ASP produced water is difficult, and the stability is greatly enhanced. ASP produced water contains a large amount of inorganic salts, which can shield the electrostatic repulsion between the surfactant ion head groups, compresses the thickness of the double electric layer, and promotes the formation of surfactant micelles. When it settles after a certain period of time, part of ASP produced water has a particle size distribution less than 100 nm, the micelles are generated in the system, which enhances the stability of ASP produced water.

Alkali Effect on Alkali-Surfactant-Polymer (ASP) Flooding Enhanced Oil Recovery Performance: Two Large-Scale Field Tests’ Evidence

Alkali-surfactant-polymer (ASP) flooding is very promising chemical enhanced oil recovery (EOR) technology which can make an incremental oil recovery factor (IORF) of 30% original oil in place (OOIP). How to choose alkali in ASP flooding remains a question for a long time. As the world’s only and largest ASP flooding application place, Daqing Oilfield has always adhered to the strategy of parallel development of strong alkali ASP flooding (SASP) and weak alkali ASP flooding (WASP), but SASP is in a dominant position, indicated by more investments and more project numbers. This leaves an impression that SASP is better than WASP. However, WASP is drawing more interest than SASP recently. Moreover, as the ASP flooding in Daqing went from field tests to commercial applications since 2014, how to comprehensively consider the benefit and cost of ASP flooding has become a new focus at low oil prices. This paper compares two typical large-scale field tests (B-1-D SASP and B-2-X WASP) completed in Daqing Oilfield and analyzes and discusses the causes of this difference. The injection viscosity and interfacial tension (IFT) for the two field test areas are substantially equivalent under the conditions of Daqing Oilfield, and WASP is better than SASP when reservoir geological conditions are considered. WASP exhibits the same IORF of 30% as SASP while having a much better economic performance. For the SASP field test, the injected strong alkali NaOH makes the test behave unlike a typical strong ASP flooding due to the presence of CO2 in the formation fluid, which well explains why IORF is much higher than all the other SASPs but scaling is less severe than others. This paper confirms that under Daqing Oilfield reservoir conditions, it is the alkali difference that caused the performance difference of these two tests, although some minor uncertainties exist. WASP is better than the SASP providing the same conditions . In addition, the detailed information of the two ASP field tests provided can give reference for the implementation of ASP flooding in other oilfields. After all, the study of ASP flooding enhanced oil recovery technology under low oil prices requires great foresight and determination.

Field Application of Alkali/Surfactant/Polymer Flood with Novel Mixtures of Anionic/Cationic Surfactants for High-Temperature and High-Water-Cut Mature Sandstone Reservoir

Summary Mixtures of anionic/cationic surfactants have never been used in enhanced oil recovery (EOR) for negatively charged sandstone reservoirs because of high adsorption. Recently, novel mixtures of anionic/cationic surfactants that produced low critical micelle concentrations (CMCs) of 3.50×10–4 wt%, ultralow interfacial tension (IFT) of 10–4 mN/m, high oil solubilization of 23, and low adsorption of 0.27 mg/g sand were developed in the laboratory for a mature sandstone reservoir with characteristics of high temperature of 81°C, high water cut of 97.8%, high recovery factor of 53.3%, and low-acid oil of 0.021 mg/g potassium hydroxide (KOH). Coreflooding results indicated that alkali/surfactant/polymer (ASP) flooding with a preslug of crosslinked polymer (CP) increased oil recovery by 24.2% of original oil in place (OOIP) over the waterflood under the optimal chemical formulation. Since January 2012, the first field application of ASP flooding in the world with highly efficient mixtures of anionic/cationic surfactants was performed for a high-temperature, high-water-cut mature sandstone reservoir to demonstrate the potential of the novel surfactant to recover residual oil from as high as 53.3% recovery factor of reserves. ASP slug and CP slug for conformance control were alternately injected. The water cut decreased from 97.9 to 90.2% and the estimated ultimate oil recovery can be increased by 14.2% of OOIP and yield up to 67.5% of OOIP.

A quantum computing-based numerical method of mixed-integer optimal control problems under uncertainty for alkali–surfactant–polymer flooding

ABSTRACT This article presents a numerical method based on quantum computing to solve two unresolved key issues for alkali–surfactant–polymer (ASP) flooding in oil exploitation: uncertainties affecting development planning and a switch control regarding injection oil wells. First, a fuzzy multi-objective mixed-integer optimal control model describing the mechanism of ASP flooding is established. Then, an improved possibilistic programming algorithm is presented to remove fuzziness and transform the model into a deterministic single-objective mixed-integer nonlinear programming (MINLP) model. On this basis, a bi-level quantum computing algorithm including quantum annealing and quantum ant colony algorithm is proposed to solve the MINLP and acquire the optimal mixed-integer control variables. The superiority of the proposed algorithm is verified by testing a number of benchmark examples. Finally, the numerical method based on quantum computing is adopted to solve successfully a mixed-integer optimal control problem for ASP flooding under uncertainty.