Comblike Polyacrylamides as Flooding Agent in Enhanced Oil Recovery

Influence of Polymer Viscoelasticity on Microscopic Remaining Oil Production

To investigate the impact of polymer viscoelasticity on microscopic remaining oil production, this study used microscopic oil displacement visualisation technology, numerical simulations in PolyFlow software, and core seepage experiments to study the viscoelasticity of polymers and their elastic effects in porous media. We analysed the forces affecting the microscopic remaining oil in different directions, and the influence of polymer viscoelasticity on the displacement efficiency of microscopic remaining oil. The results demonstrated that the greater the viscosity of the polymer, the greater the deformation and the higher the elasticity proportion. In addition, during the creep recovery experiment at low speed, the polymer solution was mainly viscous, while at high speed it was mainly elastic. When the polymer viscosity reached 125 mPa·s, the core effective permeability reached 100 × 10⁻³ μm², and the equivalent shear rate exceeded 1000 s⁻¹, the polymer exhibited an elastic effect in the porous medium and the viscosity curve displayed an ‘upward’ phenomenon. Moreover, the difference in the normal deviatoric stress and horizontal stress acting on the microscopic remaining oil increased exponentially as the viscosity of the polymer increased. The greater the viscosity of the polymer, the greater the remaining oil deformation. During the microscopic visualisation flooding experiment, the viscosity of the polymer, the scope of the mainstream line, and the recovery factor all increased. The scope of spread in the shunt line area significantly increased, but the recovery factor was significantly lower than that in the mainstream line. The amount of remaining oil in the unaffected microscopic area also decreased.

Experimental Investigation of a Mechanically Stable and Temperature/Salinity Tolerant Biopolymer toward Enhanced Oil Recovery Application in Harsh Condition Reservoirs

In search of robust polymers for enhanced oil recovery (EOR) application in reservoirs with harsh conditions, a water-soluble biopolymer was thoroughly investigated in this work to evaluate its applicability in such reservoirs. The experimental data revealed that compared to the commonly used EOR polymer, HPAM, the biopolymer was more efficient in thickening a brine solution as a result of its peculiar conformation. The presence of an electrolyte has almost no effect on the rheology of the biopolymer solution, even at an extremely high salt concentration (20 wt% NaCl). The relation between viscosity and the concentration curve was well fitted to the power-law model. Moreover, the rigid polymer chains rendered the polymer solution superior tolerance to elevated temperatures and salinity, but also led to considerable retention within tight porous media. The adsorption behavior was characterized by the average thickness of the hydrodynamic adsorbed layer on sand grains. The mechanical degradation was assessed by forcing the polymer solutions to flow through an abrupt geometry at ultra-high shear rates. The slight viscosity loss compared to HPAM proved the high mechanical stability of this polymer. These properties made it a promising alternative to HPAM in polymer flooding in the near future for high permeability oil reservoirs with harsh conditions.

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 (c _NaOH < 200 mg/L) and then became less stable with the increasing alkali concentration at a high alkali concentration (c _NaOH > 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.

The seepage flow characteristics of hydrophobically associated polymers with different aggregation behaviours in porous media

The polymer solution for oil displacement is subjected to strong shear action in practical application, and this action will affect its percolation characteristics in porous media. The effects of mechanical shearing on the solution properties and seepage characteristics of modified hydrophobically associated polymers and dendrimers with two different aggregation behaviours were studied. The results showed that mechanical shearing did not affect hydrophobic microzones. Polymers can re-associate to restore part of the network structure, thereby improving shear resistance (dendritic hydrophobically associating polymers > hydrophobically modified partially hydrolysed polyacrylamide). Polymers with 'cluster' aggregation behaviour enhanced solution performance, enabling them to establish higher resistance coefficient (RF) and residual resistance factor (RRF) in porous media but also bringing about injection difficulties. Increasing the injection rate would increase the injection pressure, but the established RF and RRF showed a downward trend. Mechanical shear pretreatment effectively improved the injectability of the polymer. To achieve polymer injection and flow control, pre-shearing polymer solution and low-speed injection can be used in field applications.

Hyper-branched structure—an active carrier for copolymer with surface activity, anti-polyelectrolyte effect and hydrophobic association in enhanced oil recovery

Herein, a hyper-branched polymer h-PMAD with, simultaneously, surface activity, an anti-polyelectrolyte effect and a hydrophobic association was prepared via aqueous solution free radical polymerization, and characterized by IR, NMR, TG–DTG and SEM. The polymer h-PMAD provided excellent comprehensive properties in terms of surface activity, thickening, water solubility, rheology and aging, which were compared with studies of HPAM and the homologous linear polymer PMAD. Specifically, the IFT value was 55.40 mN m⁻¹, 789.24 mPa s apparent viscosity with a dissolution time of 72 min, 97.72, 90.77 and 105.81 mPa s with Na⁺, Ca²⁺ and Mg²⁺ of 20 000, 2000 and 2000 mg L⁻¹, respectively. Meanwhile, the non-Newtonian shear thinning behavior had a 96.33% viscosity retention while the shear rate went from 170 s⁻¹ to 510 s⁻¹ and then returned to 170 s⁻¹ again and 0.12 Hz curve, with an intersection frequency of G′ and G′′. Also, it had 33.51% and 50.96% viscosity retention in formation and deionized water at 100 °C and a low viscosity loss in formation water at 80 °C over 4 weeks. Moreover, the h-PMAD had an EOR of 11.61%, was obviously higher than PMAD with 8.19% and HPAM with 5.88%. Most importantly, the better EOR of h-PMAD over that of PMAD testified that the hyper-branched structure provided an active carrier for copolymers with functionalized monomers to exert greater effects in displacement systems, which is of an extraordinary meaning.

Herein, a hyper-branched polymer h-PMAD with, simultaneously, surface activity, an anti-polyelectrolyte effect and a hydrophobic association was prepared via aqueous solution free radical polymerization, and characterized by IR, NMR, TG–DTG and SEM.

Modified acrylamide copolymers based on β-cyclodextrin and twin-tail structures for enhanced oil recovery through host–guest interactions

Two kinds of copolymers with host–guest interaction were synthesized, showing great potential for enhanced oil recovery.

Star-Like Branched Polyacrylamides by RAFT polymerization, Part II: Performance Evaluation in Enhanced Oil Recovery (EOR)

In the present study the performance of a series of star-like branched polyacrylamides (SB-PAMs) has been investigated in oil recovery experiments to ultimately determine their suitability as novel thickening agent for enhanced oil recovery (EOR) applications. Hereby, SB-PAMs were compared with conventional linear PAM. The effect of a branched molecular architecture on rheology, and consequently on oil recovery was discussed. Rheological measurements identified unique properties for the SB-PAMs, as those showed higher robustness under shear and higher salt tolerance than their linear analogues. EOR performance was evaluated by simulating oil recovery in two-dimensional flow-cell measurements, showing that SB-PAMs perform approximately 3–5 times better than their linear analogues with similar molecular weight. The salinity did not influence the solution viscosity of the SB-PAM, contrarily to what happens for partially hydrolyzed polyacrylamide (HPAM). Therefore, SB-PAMs are more resilient under harsh reservoir conditions, which can make them attractive for EOR applications.

Associating Polymer Networks Based on Cyclodextrin Inclusion Compounds for Heavy Oil Recovery

This work evaluates an approach to improve the enhanced heavy oil recovery performance of hydrophobic associating polymer. A polymeric system based on water-soluble hydrophobic associating polymer (WSHAP) and cyclodextrin (CD) polymer was proposed in this work. Addition of CD polymer to WSHAP forms interpolymer bridges by inclusion of CD groups with hydrophobic tails, and thereby the network structure is strengthened. The proposed system offers good viscoelasticity, pronounced shear thinning, and interesting viscosity-temperature relations. Sand pack tests indicated that the proposed system can build high resistance factor during the propagation in porous media, and its moderate adsorption phenomenon was represented by the thickness of the adsorbed layer. The relationship between effective viscosity and oil recovery increment indicated that the proposed system can significantly reduce the residual oil saturation due to the “piston-like” propagation. The overall oil recovery was raised by 5.7 and 24.5% of the original oil in place compared with WSHAP and partially hydrolyzed polyacrylamide (HPAM), respectively.

Synthesis and self-assembly of well-defined binary graft copolymer and its use in superhydrophobic cotton fabrics preparation

Schematic illustrations of the self-assembly of BGCs and photographs of superhydrophobic performance.

An anti-biodegradable hydrophobic sulfonate-based acrylamide copolymer containing 2,4-dichlorophenoxy for enhanced oil recovery

We report the synthesis of a novel hydrophobic sulfonate-based acrylamide copolymer which exhibits remarkable water solubility, excellent resistance to biodegradability, and superior ability to enhance oil recovery.

A water-soluble antimicrobial acrylamide copolymer containing sulfitobetaine for enhanced oil recovery

A novel antimicrobial copolymer containing sulfitobetaine is studied and has excellent application potential in EOR.

Rheological Properties and Salt Resistance of a Hydrophobically Associating Polyacrylamide

The rheological properties of electrolyte solution of a hydrophobically associating acrylamide-based copolymer (HA-PAM) containing hydrophobically modified monomer and sodium 2-acrylamido-2-methylpropanesulfonic sulfonate were investigated in this paper. The study mainly focussed on effects of electrolyte concentration, temperature, and shear rate on the solution rheological properties. HA-PAM exhibited much stronger salt tolerance and shearing resistance than the commonly used partially hydrolyzed polyacrylamide, and has great potential for application in tertiary oil recovery of oilfields with high salinity. The salt resistance mechanism of HA-PAM in solution was investigated by combining molecular simulation and experimental methods. The structure–performance relationship of the salt-resisting polymer may provide useful guidance for design and synthesis of novel water-soluble polymers with high salt resistance.