Oil Displacement Agent Research Articles

Enhancing oil recovery by alkane-modified molybdenum disulfide nanosheets with the optimum alkyl chain length: The balance between dispersity and hydrophobicity to achieve high interfacial activity

Alkane-modified molybdenum disulfide (AM-MoS2) nanosheets have attracted widespread interest as oil displacement agents for enhancing oil recovery due to their unique oil-water interfacial properties. However, the relationship between the interfacial activity and alkyl chain structure of AM-MoS2 is not comprehensively understood. In this study, 3AM-MoS2 nanosheets were prepared with MoS2 and alkylamines to study the effect of alkyl chain length on the oil-water interfacial activity of AM-MoS2 nanosheets under different salinity conditions. The AM-MoS2 nanosheets prepared with octylamine, dodecylamine, and octadecylamine were referred to as AM8-MoS2, AM12-MoS2, and AM18-MoS2, respectively. AM18-MoS2, which possesses the longest alkyl chain among all the samples, exhibited the highest oil-water interface adsorption ratio within the experimental concentration and salinity ranges. However, the changes in oil-water interfacial tension (IFT) did not agree with the changes in the interface adsorption ratio of nanosheets. AM18-MoS2 exhibited the best interfacial activity, and the IFT was lower than that of MoS2, AM8-MoS2 and AM12-MoS2 when the salinity was no more than 5000 mg/L, while AM12-MoS2 and AM8-MoS2 exhibited the best interfacial activity and the lowest IFT when the salinity reached 10,000 mg/L and 20,000 mg/L, respectively. Considering that the interface adsorption ratio of AM18-MoS2 was higher than that of the other samples under all the experimental conditions, the change in IFT and interfacial activity could be attributed to the change in the morphology of the adsorption layer of nanosheets. The decreased charge repulsion and the increased hydrodynamic size of nanosheets, which resulted from increased salinity, had positive and negative effects, respectively, on the morphology of the adsorption layer. The competition between the two effects resulted in the inflection point in the relationship between the IFT and salinity of AM-MoS2. The AM-MoS2 nanosheets with the optimum alkyl chain length balanced the dispersity and hydrophobicity, which contributed to achieving the best interfacial activity at a certain salinity.

Matching method between nanoparticle displacement agent size and pore throat in low permeability reservoir

Nano-particles possess desirable attributes such as small particle size, excellent injectivity, and migration performance, making them highly compatible and adaptable for addressing the water flooding requirements of the low-permeability oil reservoir. When selecting an oil displacement agent for enhancing water flooding and improving oil recovery, factors such as injectivity and migration need to be carefully considered. In this study, through a comprehensive analysis of the mechanism and technical characteristics of nano-particle oil displacement agents, the plugging and profile control mechanisms recognized by the mainstream of nano-particles are elucidated. By examining various elements including outcrop fractures, natural micro-fractures, artificial support fractures, and dynamic monitoring data, a reevaluation of the dominant channel scale governing water drive in low permeability reservoirs is conducted, thereby defining the target entities for profile control and flooding operations. Drawing upon Darcy’s percolation law and leveraging enhanced oil recovery techniques based on the classical Kozeny equation, a profile control and flooding mechanism is proposed that focuses on increasing the specific surface area of polymer particles while simultaneously reducing reservoir permeability. This innovative approach establishes a novel matching method between nano-polymer particles and the diverse media found within the reservoir. Lastly, the application of nanoparticle flooding technology in Changqing Oilfield is presented, highlighting its practical implementation and benefits.

Stability studies of dispersed systems for physicochemical methods to enhance oil recovery in the presence of a hydrophobic filler

As the formation of highly permeable zones in the reservoir results in progressive watering of the produced products, restricting the movement of the oil displacement agent is one of the main conditions for further improving the effectiveness of methods for influencing oil-saturated formations. This can be achieved by targeted tamponing with physicochemical compositions of highly conductive channels and artificial fractures. In most cases, there is a redistribution of flow and, as a result, previously undrained reservoir intervals are brought into production.The effect of tamponing is best achieved by the use of dispersed systems containing various fillers. The use of such technologies is regulated in many documents used in the work of oil and gas producing enterprises. The formation of a high-quality water barrier in such technologies depends on the stability of the working composition.The article is devoted to the study of the influence of filler hydrophobicity on the sedimentation and aggregation stability of dispersed systems. The conditions under which the systems show the least tendency to sedimentation and are aggregatively unstable are considered. It has been shown experimentally that the stability of the systems is influenced by the hydrophobic properties of the filler, which do not allow the particles to enter the aqueous phase, swell and precipitate, thereby reducing the sedimentation stability. It has been shown experimentally that the systems composed of NaQMC or PetroPam P-104 have similar indicators for the time of onset of mass deposition of particles, their average calculated deposition rates as well as viscosity characteristics.

Characterized Functional Groups of Temperature- and Salt-Resistant Copolymers and Surfactants and Their Relationships.

As the physical properties of newly discovered oil and gas reservoirs become more complex and the requirements for field development effectiveness continue to increase, the performance of polymers and surfactants, which are commonly used as chemical agents in oil field development, is facing great challenges. The determinations of temperature and salt resistance of anti-temperature and anti-salt viscosity-enhancing copolymers and low-interfacial-tension surfactants in recent years have been reviewed. The mechanism of temperature and salt resistance of distinct functional groups was discussed, and the common functional groups of temperature- and salt-resistant viscosity-increasing copolymers and temperature- and salt-resistant low-interfacial-tension surfactants were pointed out. An outlook on the molecular structure design of a new temperature- and salt-resistant oil displacement agent is presented.

Research Progress on Displacement Mechanism of Supercritical CO2 in Low-Permeability Heavy Oil Reservoir and Improvement Mechanism of Displacement Agents.

With the continuous growth of global energy demand and the late stage of conventional oilfield exploitation, the demand for developing and utilizing low-permeability heavy oil reservoirs is becoming increasingly urgent. However, the exploitation of low-permeability heavy oil reservoirs faces many challenges due to their high viscosity, low permeability, and complex geological conditions. To overcome these challenges, researchers have gradually introduced SC-CO2 as an oil displacement agent in the exploitation of heavy oil reservoirs. However, the oil displacement mechanism of SC-CO2 in low-permeability heavy oil reservoirs and its improvement mechanism are still not completely understood. The article provides a detailed study and understanding of the oil displacement mechanism of SC-CO2, which involves the expansion of heavy oil volume through SC-CO2 dissolution. This mechanism reduces the capillary resistance and flow resistance during the oil flow process. The permeation of CO2 disrupts the internal structure and arrangement of heavy oil, reducing its viscosity. CO2 extracts both light and heavy components from the heavy oil, reducing the residual oil saturation. In addition, the mechanism of improving the effect of oil displacement agents such as nanoparticles, polymers, and surfactants on SC-CO2 displacement was also explored. By further exploring the mechanisms and improvement mechanisms of SC-CO2 displacement for heavy oil, it can guide the selection and optimization of oil displacement agents. Furthermore, understanding the mechanism can also provide a theoretical basis for engineering practice and technical innovation. While the research on CO2 flooding is analyzed and evaluated, the obstacles and challenges that still exist at this stage are indicated, and future research work on CO2 in low-permeability heavy oil reservoirs is proposed.

The effect of HMPAM on performance of nonionic polyether water clarifier from the perspective of HLD theory

Nonionic polyether water clarifier is commonly used in the treatment of produced water from offshore oilfield. At the meantime, hydrophobically modified polyacrylamide (HMPAM) is one of the commonly used polymer oil displacement agents. Predicting the influence of HMPAM on the performance of nonionic polyether water clarifier is of great significance for the treatment of produced water. This work explored the influence of different HMPAMs on the hydrophilic-lipophilic deviation (HLD) equation of a typical nonionic polyether water clarifier AE411 based on the HLD theory, and predicted their influences on the performance of AE411. The results showed that HMPAM had no effect on the parameter K (reflecting the interaction between AE411 hydrophilic groups and oil phase) and ct (reflecting the temperature sensitivity of AE411) in HLD equation of AE411, but reduced the parameter Ccn (reflecting the micelle structure of AE411 in water) and led to an increase in temperature corresponding to AE411′s HLD = 0. It was predicted that higher temperature was needed to ensure the performance of AE411. The experimental results of produced water treatment confirmed this prediction. The results of the paper validated the reliability of HLD application in the field of produced water treatment and provided some guidance for the development of nonionic polyether water clarifier.

Synergistic mechanism of enhanced heavy oil recovery by compound flooding using 3D visualization model

Most of oilfields have entered the development stage of high water-cut and low recovery factors, and stabilizing oil production and controlling water production are the key to enhancing subsequent oil recovery. Adopting the 1/4 five-point injection-production well pattern, the chemical flooding experiments were conducted using a three-dimensional (3D) visualization sand-pack model with liquid drain orifices. A real-time image acquisition and dynamic observation device for detecting droplet textures as fluid flowing was developed with experimental system. In heterogeneous reservoirs with a high permeability contrast, the effects of oil-displacement agents on production dynamics, sweep morphology, and emulsifying characteristics of remaining oil at different locations were investigated to reveal the synergistic mechanism of compound flooding for enhanced oil recovery. The results showed that, in the main streamline region, the mean droplet diameter decreased, the distribution density increased first and then decreased, and the maldistribution decreased first and then increased with an increase in injection volume of the compound system. In the vertical region with the main streamline, the mean diameter and maldistribution reduced, and the distribution density increased owing to the synergistic mechanism. The viscosity reducer can increase sweep efficiency by 8.34% and recovery factor by 5.95% due to the viscous crossflow in the high permeability channel. The compound system can increase sweep efficiency by 15.92% and recovery factor by 12.67% due to the synergistic effect of emulsifying-tapping, emulsion plugging conversion, and profile control. Therefore, chemical compound flooding has great potential of enhancing heavy oil recovery in heterogeneous reservoirs due to the synergistic effect of the compound system.

Dispersion stability and interfacial properties of modified MoS2 nanosheets for enhanced oil recovery

As an emerging technology for enhanced oil recovery that is highly efficient, cost-effective, and environmentally friendly, nanofluids have gained increasing attention. However, improving the dispersion stability of nanofluids to enhance oil displacement efficiency remains an open challenge. In this study, a variety of modified MoS2 nanosheets were synthesized and their stability in brine and basic properties relevant to oil displacement were systematically investigated. The results demonstrated that both modification methods were effective to some extent. However, compared with physically adsorbed, chemically modified MoS2 nanosheets by sulfur vacancies exhibited superior performance. It was reflected in their good stability in brine, low interfacial tension, and effective emulsifying ability. These advantageous properties enabled them to enhance oil recovery in a significant manner. This work revealed the basic properties of modified MoS2 nanosheets, especially the dispersibility in brine. It was expected to design suitable chemical oil displacement agents for different reservoir conditions and provide guidance for practical application.

Experimental study on enhancing heavy oil recovery by mobility control oil displacement agent

The suitable concentration of mobility-controlled oil displacement agent was selected through laboratory experiments, and the development mechanism of mobility-controlled oil displacement agent in the water flooding process was studied. The results show that when the concentration of mobility control oil displacement agent is 0.15 %, the viscosity reduction effect is the best. Fluid injection pressure can be reduced by mobility controlled oil displacement agent. The mobility control oil displacement agent can improve the oil displacement efficiency, and the recovery rate of Tuha heavy oil is increased from 36.58 % to 65.13 %. The mobility control oil displacement agent has a strong effect of solubilization and viscosity reduction at low shear rate of the formation, and has a viscosity increase for water, so it can improve the development effect.

Estimation of the Efficiency of Oil Displacement by a Micellar Solution with Addition of Nanoparticles Based on a Bulk Model of Porous Medium

The results of laboratory studies of the features of processes of flow through a porous medium are given for a physical model of the porous medium obtained by sintering glass beads. The program for manufacturing physical models is described and the results of the efficiency of displacement of vaseline oil by various compositions are presented. Water, mineralized water, micellar solutions, nanofluids, and micellar solutions with addition of nanoparticles were considered as the displacement agents. Based on an analysis of images, curves of variation in the saturation of the model porous medium with vaseline oil in the process of its displacement by various compositions are obtained. The micellar solutions with addition of nanoparticles were shown to be the most effective oil displacement agents in comparison with other presented compositions.

EOR mechanism of fracture oil displacement agent for ultra-low permeability reservoir

Due to the low permeability, small pore throat, and poor pore connectivity of ultra-low permeability reservoirs, fracturing was required to improve the flow environment of oil in the reservoir during its development. The combination of fracturing and oil displacement could reduce the complexity of the development of ultra-low permeability reservoirs. It was feasible to synthesize new surfactants to prepare fracturing oil displacement agents, but the research and development of new surfactants were difficult and costly. This paper aimed to experimentally investigate the imbibition displacement mechanism of fracturing flooding by combining the surfactant of chemical flooding with the fracturing fluid. With the conditions of the ultra-low permeability reservoir in block Y of Changqing Oilfield, the mechanism of remaining oil start-up and fractured oil displacement agent enhanced oil recovery in the ultra-low permeability reservoir was studied by microfluidic model experiment and NMR experiment. A mixture of fracture oil displacement agents was obtained by mixing heavy alkyl benzene sulfonate surfactant, a nonionic surfactant, and a betaine-type amphoteric surfactant. HAS-6C, HAS-5E, and HAS-5G were selected for their interfacial tension reaching 10−3 mN/m. Oil–water​ interfacial tension of HAS-5E was the lowest, which can be reduced to 10−4 mN/m. The ability to alter the wettability of HAS-6C was the most significant, which could make the contact angle go down to 64.5°. The multi-round dynamic and static imbibition experiments showed that the combination of selected surfactant and slickwater can greatly improve the imbibition recovery, of which HAS-6C could enhance oil recovery by 17%. The HAS-5E system with the lowest interfacial tension had the best effect of starting clustered residual oil, and the clustered residual oil saturation was reduced by 48.8%. The HAS-6C system with stronger wettability had the best effect of starting throat-like residual oil, and the throat-like residual saturation was reduced by 10.8%.

Highly thermoconductive biogel for enhancing thermal efficiency and soil self-remediation in heavy oil recovery

The thermal recovery of heavy oil is an energy-intensive process with serious soil contamination due to its low energy efficiency and refractory petrolic/metallic pollutants emissions. In this work, a thermoconductive lignin-based hydrogel CaLS-CTS/h-BN was designed and synthesized for thermal energy conservation and soil self-remediation in thermal recovery, as a profile-control and oil-displacement agent. From experimental results, with the assistance of CaLS-CTS/h-BN gel, the thermal efficiency and cumulative oil-steam ratio of steam flooding were enlarged by 260% and 293% (up to 41.3% and 0.36), as input energy declined (reduction ratio 84.8%) from 15.08 kJ·(mL oil)−1 to 2.29 kJ·(mL oil)−1, through improving heating profile and strengthening heat transfer. Meanwhile, the rapid biodegradation of CaLS-CTS/h-BN biogel alleviated the formation damage and preserved subsequent productivity. On the other hand, after application of CaLS-CTS/h-BN gel, the natural degradation ratio of petroleum pollutants in soil was increased by 254% up to 46% due to the bio-stimulation and bio-ventilation effect of the biogel. Heavy metal content of oilfield soil was reduced by 35.8 wt% (from 17.3 g·(kg soil)−1 to 10.9 g·(kg soil)−1) with multiple heavy metal contaminants (including Cd, Cr, Cu, Zn, Mn, Pb and Fe) chelated and immobilized by the biogel. This study offered a green adjuvant agent for cleaner production of heavy oil.

Laboratory experiment and field application of chemical assisted steam flooding

ABSTRACT There are serious problems such as steam channeling and low oil-steam ratio when it comes to steam flooding. In order to improve its performance and to enhance oil recovery, foam agents and oil displacement agents are used to enhance the sweep efficiency and the displacement efficiency in steam flooding process. The design, development, and syntheses of high-performance low-cost foam agent and oil displacement agent were put forward in this paper. Evaluation experiment results showed excellent foaming performance and the high-temperature resistance of the foam agent. In addition, good interfacial performance and thermal stability of the oil displacement agent were also observed. The developed system was able to achieve ultra-low interfacial tension under steam flooding conditions. Laboratory experiments of chemical assisted steam flooding showed that the injection of the high-temperature foam agents and oil displacement agents totally enhanced oil recovery of 11.67%. Chemical assisted steam flooding field test has also been carried out in Gudao Zhongerbei Block of Shengli Oilfield. By June 2020, the cumulative oil production in the pilot area was 4.02 × 105 t with the reserve recovery percent of 54.6%, the enhanced oil production was 3.56 × 105 t and the enhanced oil recovery factor was 19.3%.

Molecular Dynamics Simulation of the Synergistic Effect of Alkali/Surfactant/Polymer on the Formation and Stabilization of Water-Based Foam Systems.

The stable maintenance effect of a chemical oil displacement agent on a foam liquid film usually creates problems with the oilfields surface system. To achieve comprehensive insights into the influence mechanism of these chemical agent components on the foam liquid film, an "SDBS/HPAM/OH-" water-based foam simulation system and corresponding control systems were constructed by adjusting the categories and quantities of component molecules by molecular dynamics (MD) simulation. The simulated results indicated that the foam stability follows the order of "SDBS/HPAM/OH-" system > "SDBS/HPAM" system > "SDBS" system. The smaller the inclination angle of the SDBS molecular tail chain, the greater the tendency of the SDBS molecular configuration to be "upright" at the gas-liquid interface, which is not conducive to preventing the aggregation and penetration of gas molecules at the gas-liquid interface. Although the presence of HPAM molecules can significantly enhance the stability of the liquid film by restricting the liquid film's drainage and the diffusion of gas molecules, the addition of HPAM molecules would weaken the formation ability of the foam liquid film. Through decreasing the aggregation of cations around the co-adsorption layer, OH- not only enhances the interfacial activity of SDBS molecules, but also reduces the electrostatic repulsion between -COO- groups on the HPAM molecular chain, which makes the foam more stable. With an increase in the pH, SDBS concentration, and HPAM concentration, the stability of foam liquid film was strengthened. These results are helpful in facilitating new insights into the formation and stabilization mechanism of water-based foams. In particular, they provide support for the development and application of new defoaming technologies.

Mechanism and influencing factors of enhanced oil recovery for active SiDots nanofluid assisted fracturing-drainage in low permeability reservoirs: An experimental and numerical simulation study

Fracturing-drainage in low permeability reservoirs is a special method to facilitate oil production, however, conventional chemical oil displacement agents cannot adequately take advantage of this technology. Active SiDots nanofluid has special surface/interface properties and excellent stability that can contribute to improving the effect of fracturing-drainage. This paper investigates the influencing factors and mechanisms of active SiDots nanofluid assisted fracturing-drainage to enhance oil recovery (EOR) through experiments and reservoir numerical simulation. The results on the performance of the active SiDots nanofluid show that 0.10 wt% concentration was sufficient to reduce the oil-water interfacial tension from 20 mN/m to 0.32 mN/m and modify the oil-wet core to water-wet. Experimental and reservoir numerical simulation results indicate that the incremental oil recovery after the active SiDots nanofluid fracturing-drainage was more than 10%, which was more effective than surfactant alone. The optimum injection concentration and volume of active SiDots nanofluid were 0.10 wt% and 0.6 PV, respectively. To improve the utilization of active SiDots nanofluid, the well shut-in time should be at least 24 h. One-cycle active SiDots nanofluid injection was more conducive to replenishing the formation energy and expanding the swept volume. The field injection rate of the SiDots nanofluid should not be too high to prevent breakthroughs. The EOR experimental results indicate that the fracturing-drainage could increase the injection volume to replenish energy and reduce the active SiDots nanofluid adsorption loss thereby effectively peeling the oil film. This paper addresses the supply shortage of conventional chemicals used for fracturing-drainage in low-permeability reservoirs and expands the study of the influencing factors and mechanisms of fracturing-drainage.

Mechanism of enhanced oil recovery by fuzzy-ball fluid as a novel oil-displacement agent

Fuzzy-ball fluid is a two-phase fluid composed of fuzzy-ball and base fluid. It can enhance oil recovery by approximately 30% after water flooding and polymer flooding, which has been demonstrated in laboratory experiments and field applications. However, the EOR mechanism of fuzzy-ball fluid still needs further research. In this study, the microstructure of fuzzy-ball was observed using optical and cryo-scanning electron microscopy. The EOR mechanism of fuzzy-ball fluid was investigated by the microscopic glass etching model experiment and inter-molecular force calculation. EOR contribution ratio of three parts of fuzzy-ball was evaluated by the single core flooding experiment. Results showed that fuzzy-ball was further subdivided into fuzzy-ball structure and floss structure. Correspondingly, the EOR effects of fuzzy-ball fluid were mainly divided into three parts: (a) base fluid. Emulsification was the main way for base fluid to enhance oil recovery; (b) fuzzy-ball structure. According to the distribution characteristics of residual oil, the EOR mechanisms of fuzzy-ball structure were mainly as follows: wedging displacement for membranous oil, squeezing-carrying mechanism for columnar oil, and extruding-squeezing mechanism for blind-end oil; (c) floss structure. Floss structure enhanced oil recovery mainly through entanglement and carrying mechanism. Moreover, the EOR contribution ratio of base fluid, fuzzy-ball structure, and floss structure are 18.35%, 50.94%, and 30.71%, respectively. This study elucidates the EOR mechanism of fuzzy-ball fluid and provides guidance for its subsequent field application and performance improvement.

Salt-Responsive Phenol Formaldehyde Resin: Changes of Interface Energy on the Aggregation Process.

Phenol formaldehyde resins (PFRs) as a colloidal oil displacement agent were commonly used to plug pores in crude oil reservoirs for enhanced oil recovery (EOR). The aggregation-dispersion and charging behavior of PFR may affect the rheology and plugging performance of the suspension. To understand the aggregation-dispersion and charge of PFR, turbidity, dynamic light scattering, and electrophoretic light scattering experiments were carried out at pH = 10 with different concentrations of salt solutions (NaCl, MgCl2, CaCl2, NaCl/MgCl2, and NaCl/CaCl2). The aggregation rate and ζ-potential were measured, and the critical coagulation concentration (CCC) and critical coagulation ionic strength (CCIS) were further obtained. Based on the triple-layer surface complexation (TL) model, the adsorption ability of cations and the surface characteristics of the PFR particles were studied, and these differences were explained by interface energy. Thus, Derjaguin-Landau and Verwey-Overbeek (DLVO) theory modified by interface energy was applied to explain the aggregation behavior of PFR particles in different types of ion systems. We concluded that, in the presence of multiple ions, DLVO theory modified by interface energy has good applicability to the aggregation-dispersion of PFR particles.

Effect of oil displacement agent on corrosion behavior of NaCl - Alkali/ Surfactant/ Polymer flooding pipeline steel

The research examined the effect of oil displacement agent (Hydrolyzed polyacrylamide, Sodium petroleum sulfonate, NaCl) on corrosion behavior of 20# steel in simulated NaCl ASP flooding solution. Scanning electron microscope (SEM), Transmission Electron Microscope (TEM), X-ray Photoelectron Spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were performed to investigate the corrosion mechanism of oil displacement agent on carbon steel. The results demonstrated HPAM (hydrolyzed polyacrylamide) and SPS (sodium petroleum sulfonate) can be adsorbed on the surface of carbon steel to played a role in corrosion inhibition. For-HPAM, the corrosion inhibition rate decreases at high concentrations, which was ascribed to the saturation of adsorption amount and the thinning of corrosion product layer at higher concentrations. For-SPS, the formation of hemi-micellar aggregates caused desorption of the inhibitor from the metal/solution interface at higher concentrations. For -NaCl, NaCl promoted the occurrence of corrosion. Although the adsorption of oxygen on the surface of carbon steel was inhibited by a higher concentration of Cl−, a corrosion cell was formed under the action of the adsorption layer of HPAM and SPS, which promoted localized corrosion.

Investigation on the Injection Pattern of Intermittent Natural Gas Flooding in Ultra-Low Permeability Reservoirs

Natural gas is a viable oil displacement agent in ultra-low-permeability reservoirs due to its good fluidity. It can also cause gas channeling during continuous injection, which limits its oilfield application. In order to relieve gas channeling during natural gas flooding, the injection mode should be changed. The use of intermittent natural gas injection (IGI) after the continuous natural gas injection in an ultra-low-permeability reservoir is proposed, and optimization of the injection parameters is discussed. The results show that IGI can be divided into three stages, the gas injection stage, the well shutting stage and the oil production stage. With the increase in injection time, the oil recovery enhances obviously as a result of IGI because the gas fingering can be controlled at the well shutting stage, and the gas/liquid ratio grows slowly because the gas breakthrough can be reduced at the oil production stage. The oil recovery improves with the increase in cycle time of IGI, while the increase rate reduces evidently after the cycle time reaches 360 min. The oil recovery increment is low if the cycle index exceeds 3 in the ultra-low-permeability reservoir. Thus, the optimal cycle time for each round and the appropriate cycle index of IGI are 360 min and three rounds.

New Technique for Enhancing Residual Oil Recovery from Low-Permeability Reservoirs: The Cooperation of Petroleum Hydrocarbon-Degrading Bacteria and SiO2 Nanoparticles.

Residual crude oil production from low-permeability reservoirs has become a huge challenge because conventional recovery techniques are inefficient. Nanofluids as a new type of oil-displacement agent have become a hot topic in recent years to enhance oil recovery (EOR) in reservoirs. However, the imperfection of agglomeration, dissolution, and instability of nanofluids in reservoir environments limit their ability to drive oil. Here, a novel "microbial-nanofluid" composed of petroleum hydrocarbon-degrading bacteria (PHDB, namely Bacillus cereus) and SiO2 nanoparticles was proposed as a potential new technology for enhancing residual oil recovery. The micromodel displacement test results showed that the optimum composite concentration of "microbial-nanofluids" were PHDB (7.0%, v/v) and SiO2 nanoparticles (100 mg/L), and the residual oil recovery was increased by 30.1% compared with waterflooding (68.8%). Moreover, the morphological characteristics of residual oil mobilization after "microbial-nanofluid" flooding were mainly small and dispersed oil droplets in the excessive areas, and the dead-end areas were almost clean with mobilization. Furthermore, the cooperation mechanism of four kinds of "microbial-nanofluids" to enhance the residual oil recovery in low-permeability reservoirs was preliminarily clarified, namely the co-emulsification of oil, working together to unclog oil clog, microbial-nanofluid self-assembly, and structural disjoining pressure. This study demonstrated that PHDB-SiO2 nanoparticle composite flooding technology provided a significant potential for the EOR from low-permeability reservoirs.