Hydrophobic Associative Polymer Research Articles

Preparation and performance evaluation of a low‐damage fracturing fluid for unconventional reservoirs

AbstractThe characteristics of tight matrix, underdeveloped natural fractures, small pore throat radius, poor pore connectivity, and abundant clay minerals result in a high potential for damage to the tight sandstone reservoirs of the Shaximiao Formation in the Qiulin Block in the Sichuan Basin. In order to reduce the retention damage caused by fracturing fluid to the tight sandstone reservoir, a low damage fracturing fluid system applicable to the target reservoir is developed in this work, and the indoor performance meets the requirements of on‐site fracturing operation. A low‐damage, heat‐resistant, shear‐stable amphiphilic polyacrylamide (PAAD) was prepared by free radical polymerization in aqueous solution using acrylamide, acrylic acid, and methacryloyloyloxyethyl dimethyloctadecyl ammonium bromide (DM18) as the monomers. The amphoteric polyacrylamide was characterized by Fourier infrared spectroscopy, nuclear magnetic resonance spectroscopy (1H NMR), light scattering molecular weight determination, and thermogravimetric analysis. Fracturing fluids were formulated with the amphiphilic hydrophobic associative polymer PAAD as a drag‐reducing agent, the fluorine‐containing and nonionic complex surfactant FD1 as a clean‐up additive, CT10‐4B as a bactericide and CT1‐12 as an emulsion breaker. The fracturing fluid formulation was preferred, and the performance of the fracturing fluid was evaluated in terms of temperature resistance and shear resistance, drag reduction, anti‐expansion, and core damage. The fracturing fluid showed good temperature and shear resistance, with a viscosity retention of 58.4% at 120°C and 170 s−1 shear for 1 h. At a loading of 0.1%, the drag reduction rate reaches 72.3%, the anti‐expansion rate of the gel‐breaking fluid is 86.04%, and the damage rate to the tight sandstone core is 16.25%. The results show that the fracturing fluid has good heat resistance and shear stability, as well as low damage and good resistance reduction and anti‐expansion properties. This work can provide new strategies for designing polymeric fracturing fluids with low damage, good heat resistance and shear stability.

Secondary utilization of self-suspending proppant's coating polymer: Enhance oil recovery

Fracturing is associated with significant economic costs, and the loss of the utility of the self-suspending proppants' coating polymer after fracturing appears highly wasteful. To enhance the utilization of the self-suspending proppant's coating polymer, we propose a novel concept: the secondary utilization of coating polymer, enabling the coating polymer to gel-breaking within the reservoir and generate surface-active substances, thereby enhancing the oil recovery efficiency. To realize this concept, this study designed and synthesized a hydrophobic associative polymer, which was combined with ceramic proppant to form self-suspending proppant. Using the surface-active monomer octadecyl dimethyl allyl ammonium chloride (DMDAAC-18), acrylamide (AM), acrylic acid (AA), and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) via aqueous free-radical copolymerization synthesized the PAAAD (Polymer (AM/AA/AMPS/DMDAAC-18)). PAAAD has demonstrated excellent thickening properties, with a viscosity of 240.01 mPa s at a concentration of 6 g/L in shear rate 170s−1. Its solution exhibits high viscoelasticity, and a loss factor (tan δ) < 1 over the frequency range of 0–20 Hz at a shear stress of 0.56 Pa indicates that it behaves like a viscoelastic solid with gel-like characteristics, which is beneficial for proppant suspension. The gel-breaking solution of PAAAD reduced surface tension (29.33 mN/m at a PAAAD concentration of 6 g/L), converted oil-wet rocks to water-wet conditions (reducing the contact angle of oil-wet shale to 46.7° and of oil-wet sandstone to 19.9°), and enhanced shale imbibition oil recovery efficiency in 16.5%. The basic properties of self-suspending proppants meet the Chinese Petroleum Industry Standard SY/T 5108-2014 and exhibit good suspension properties, with sedimentation of 1.7 mm in 40 min at a sand ratio of 15%. This study is the first to propose the secondary utilization of the self-suspending proppant's coating polymer, significantly enhancing their utilization value.

Development and mechanism research of hydrophobic associative polymer drag reducing agents

ABSTRACT The challenge of insufficient proppant transportation capacity in slick water remains unresolved. To tackle this concern, a hydrophobically associating water-soluble polymer (HAWP), characterized by a low molecular weight (MW) of 8.11 × 105 g/mol, was successfully synthesized via a photo-initiation method. The drag reduction mechanism of the material was characterized through nuclear magnetic resonance and rheological performance testing. The drag reduction mechanism of the material was characterized through nuclear magnetic resonance and rheological performance testing. The results show that in comparison to conventional drag reducers in slick water with an average MW of approximately 1 × 107 g/mol, HAWP demonstrates significantly reduced MW. The rheological test results indicate that upon addition of sodium dodecyl benzene sulfonate (SDS, 200 mg/L) to the HAWP solution (0.3 wt%), the storage modulus experienced a substantial increase from 0.14 Pa to 7.42 Pa, demonstrating enhanced mechanical properties. Meanwhile, drag reduction (DR) tests showed that the efficiency of drag reduction achieved by the polymer system (PS) drag reducer was comparable to that of conventional linear polymers. This research achievement effectively addresses the challenges of low molecular weight and resistance reduction encountered in previous endeavors.

Experimental investigation of the rheological behavior and micro-morphology of the wormlike micelle cross-linked with polyelectrolyte-grafted nano silica and the associative polymer

This paper has investigated the rheological behavior and micro-morphology of CTAC wormlike micelle (WLM) which cross-linked with polyelectrolyte-grafted nanosilica (PEN) and nonionic hydrophobically-associating polymer (HAP). Cryo-transmission electron microscopy (Cryo-TEM) is adopted to observe the micro-morphology of the associative structure. Results show that PEN cross-linked with CTAC wormlike micelle exhibits higher zero-shear viscosity than the non-modified nano silica, and this viscosity is continuously raised as the PEN concentration is increased. PEN-micelle complex has excellent anti-salt properties and its zero-shear viscosity is increasing in a KCl concentration range of 0–10%. The shear viscosity of wormlike micelle is enhanced by HAP and polymer molecules dominate the rheological characteristic of the mixed fluid. The shear viscosity of HAP-micelle fluid is further increased by PEN. However, the rheological characteristic of the micelle-HAP-PEN complex is identical to that of wormlike micelle. The elasticity of wormlike micelle is noticeably enhanced by cross-linking with PEN and HAP. They stimulate the formation of micelle to significantly increase the length and rigidity of wormlike micelle. Surfactant molecules spontaneously arrange on the surface of PEN and grow outwards, which associates with HAP to generate the tighter three-dimensional network structure.

Simulated evaluation of the degradation of hydrophobically associative polymers in the formation

AbstractIn this work, indoor physical simulation experiments were used to examine the effects of shear, thermal, chemical, and microbial degradation on the properties of the hydrophobic associative polymer AP‐P4. It was discovered that the viscosity of the polymer solution generally decreased as the shear time was extended. The larger the shear strength, the lower the solution viscosity. Fitting of the nonlinear equation of solution viscosity with shear time, η = 12,988 t−1.08. When thermal degradation started, the solution viscosity first started to rise, however, this phase was just a short one. The viscosity of the solution gradually started to decrease as the thermal degradation period grew. In addition, the trends of properties like hydrokinetic radius, hydrophobic connectivity, and hydrolysis essentially followed the same patterns as those of solution viscosity. At the beginning of the degradation process, the viscosity retention of the polymer solution without oxygen is significantly higher than that of the aerobic environment. However, the difference between the two becomes smaller as the degradation time increases. In addition, the AP‐P4 had good temperature resistance and aging resistance capabilities when iron ions were present. Finally, it was discovered that AP‐P4 had a strong antibacterial effect, which decreased the viscosity brought on by microbial action.

Molecularly designed nonionic hydrophobic association polymers with anti-salt capacity: Enhancing drag reduction at high mineralization levels

The development of advanced anti-salt drag reduction (DR) agents is crucial for enhancing oil recovery rates, particularly in highly mineralized saline water where the network structure of polymers is prone to disruption, resulting in decreased DR. To address this problem, by carefully designing the structure of the hydrophobic association polymer, a new hydrophobic monomer called APO-10 was introduced, which successfully integrated water-soluble groups, and greatly enhanced the polymer's association properties in an aqueous solution. This ingenious approach produced a stable and robust network structure that can effectively resist the harmful effects of salt ions. PAPO-10 was synthesized through free radical polymerization and has hydrophilic EO chains that enhance its water solubility, enabling better extension of the hydrophobic long chain on the tail in solution. This facilitates the association between molecular chains, leading to the formation of a stable network structure even at low concentrations. PAPO-10 demonstrates remarkable properties, including rapid dissolution and exceptional resistance to salt. It delivers a remarkable DR of up to 78.2466 % at a concentration of 500 mg/L, dissolving within a mere 2 min in aqueous solutions. Molecular dynamics simulations confirmed that PAPO-10 exhibits strong polymer chain binding in solution, consistent with experimental results. Overall, this study provides valuable insights into the development of anti-salt polymers in slick fracturing.

Polymerization Behavior and Rheological Properties of a Surfactant-Modified Reactive Hydrophobic Monomer

The structures and properties of hydrophobic association polymers can be controlled using micelles. In this work, we synthesize a reactive hydrophobic surfactant monomer, KS-3, from oleic acid, N,N-dimethylpropylenediamine, and allyl chloride. A strong synergistic effect between KS-3 and cocamidopropyl betaine in aqueous solution enhances the hydrophilic dispersibility of KS-3, thereby transforming spherical micelles into cylindrical micelles. KS-3 was grafted onto a polyacrylamide chain via aqueous free-radical polymerization to obtain RES, a hydrophobic association polymer. Structural analysis revealed that the RES polymers assembled in wormlike micelles were more tightly arranged than those assembled in spherical micelles, resulting in a compact network structure in water, smooth surface, and high thermal stability. Rheological tests revealed that the synthesized polymers with wormlike and spherical micelles exhibited shear-thinning properties along with different structural strengths and viscoelasticities. Therefore, controlling the micellar state can effectively regulate the polymer properties. The polymers obtained through wormlike micelle polymerization have potential applications in fields with high demands, such as drug release, water purification, and oilfield development.

Study on the Synthesis and Properties of a New Salt-Resistant Drag Reducer

Summary To solve the problem of poor salt resistance of conventional drag reducers, a hydrophobic associative polymer drag reducer was prepared by inverse emulsion polymerization with acrylamide (AM), methacrylic acid (MAA), 2-acrylamide-2-methylpropane sulfonic acid (AMPS), and hexadecyl dimethyl allyl ammonium chloride (C16DMAAC) as the main monomers. The synthetic product was confirmed as the target product by infrared (IR), nuclear magnetic resonance (NMR), and mass spectrometry (MS). The viscosity-average molecular weight of the prepared drag reducer is 1100×104 g/mol. The pipeline friction results show that the drag reducer has good friction reduction and salt resistance. When the concentration in clean water is 0.06%, the maximum friction reduction rate is 71.1%. When the salinity is 5×104 mg/L, the calcium ion concentration is 2000 mg/L, and the suspended solid content is 500 mg/L, the maximum friction reduction rate is 68.9% when the concentration of the drag reducer is 0.06%. Salt water will not significantly lower the friction reduction rate. If the concentration of the drag reducer is increased to 0.08%, the maximum drag reduction rate will reach 73.8%. The microrheological test results of the friction reducer solution show that, at 0.2% concentration, there is no network structure between friction reducer molecules, which is consistent with Newtonian fluids possessing a certain viscosity. The elasticity index (EI) of the drag reducer solution is basically unchanged over time, maintaining good friction reduction and sand-carrying performance during the shearing process of large displacement pumping.

Preparation and investigation of self-healing gel for mitigating circulation loss

Lost circulation is a common and complex downhole accident in the process of oil and gas drilling. Traditional bridge plugging material has the limitation of poor adaptability to lost formations. Therefore, this study synthesized a new self-healing plugging material to improve the plugging success rate; specifically, the hydrophobic association polymer lauryl methlacrylate-acrylamide-acrylic acid containing Fe3+ was modified via curdlan to form a composite gel with high strength and self-healing properties. The self-healing time, mechanicalness and rheological properties of the self-healing gel were systematically evaluated. The results showed that the modification of curdlan could significantly improve the mechanical properties and rheological strength of self-healing gel, and the chelating structure formed by Fe3+ and carboxyl groups could further enhance the mechanical properties of the self-healing gel. Toughness and storage modulus of the LF0.15C2 selfhealing gel with the introduction of curdlan and Fe3+ could reach 30.2 kJ/m3 and 3,458 Pa, respectively. Compared with conventional gel materials, composite gels with self-healing properties exhibited better pressure-bearing capacity of 2.5 MPa, and could effectively avoid causing plugging at the entrance of the fractures by high-concentration inert material and improve the pressure-bearing capacity. In addition, the plugging mechanism of the self-healing gel modified via curdlan in formation fractures was analysed in detail. The self-healing gel modified via curdlan prepared in this work has application potential as a lost circulation material in the field of oil and gas drilling. Cited as: Wang, R., Wang, C., Long, Y., Sun, J., Liu, L., Wang, J. Preparation and investigation of self-healing gel for mitigating circulation loss. Advances in Geo-Energy Research, 2023, 8(2): 112-125. https://doi.org/10.46690/ager.2023.05.05

Preparation and Performance Evaluation of a Temperature and Salt Resistant Hydrophobic Associative Weak Polymer Gel System.

We targeted high-temperature and highly saline old oil fields, whose environmental conditions could be attributed to the significantly high heterogeneity cause by long-term water flooding. The Huabei Oilfield was chosen as the research object. We developed a hydrophobic functional monomer-polymer with temperature and salt resistance by introducing the temperature-resistant and salt-resistant monomer NVP and a hydrophobic functional monomer into the main chain for copolymerization. We used a crosslinking agent with phenolic resin to prepare a weak gel system that showed temperature and salt resistance and investigated its temperature and salt resistance, infective property, plugging performance, liquid flow ability, micropore throat migration, and plugging characteristics. The results obtained using the infrared spectroscopy technique revealed the successful preparation of the phenolic resin crosslinker. The weak gel exhibited good temperature and salt resistance when the polymer concentration was 2000 mg/L, the cohesion ratio was 1:1.5, the additive concentration was 2000 mg/L, the reservoir temperature was 120 °C, and the injected water salinity was 40,300.86 mg/L. The average viscosity retention rate of the 90-day weak gel reached more than 80% and its microstructure was examined. The coreflow experiment results revealed that the weak gel system was characterized by good infectivity. After plugging the weak gel, the effect on the direction of the liquid flow was evident and the flow rate of the low permeability layer increased to a maximum of 48.63% under conditions of varying permeability levels. A significant improvement in the water absorption profile was achieved. The plugging was carried out through a sand-filling pipe under varying permeability conditions and the pressure measuring points in the sand-filling pipe were sucessfully pressurized. The migration ability of the weak gel was good and the blocking rate was >85%.

Construction of fracturing fluid with excellent proppant transport capacity using low molecular weight hydrophobic association polymer and surfactant

Slick water fracturing fluid is widely used for fracturing unconventional reservoirs such as shale and tight gas, and it has aided in developing unconventional oil and gas reservoirs. However, the problem of slick water in terms of its weak proppant transport capacity has not been effectively solved. Conventional methods of increasing the proppant transport capacity of a fracturing fluid by increasing viscosity and pumping rate have resulted in serious reservoir damage and increased costs, showing more and more limitations. To address this issue, a low molecular weight polymer/surfactant (LMPS) fracturing fluid system was developed. LMPS increased the fluid elasticity through the interaction between the hydrophobic groups on the polymer and the surfactant while maintaining low viscosity, thus obtaining excellent proppant transport capacity. The low molecular weight polymer is a type of hydrophobic association water-soluble polymer (HAWSP) prepared by photoinitiation. Its viscosity-average molecular weight was determined to be 1.24 × 106 g/mol, much more than that of a typical drag reducer of traditional slick water (about 1 × 107 g/mol). The low molecular weight of HAWSP is conducive to preparation, dissolution, pumping, and reducing the damage of polymer to the reservoir. When 300 mg/L of sodium dodecyl benzene sulfonate (SDBS) surfactant was added to a 0.2 wt% HAWSP solution, it formed a robust self-assembled network that significantly enhanced the elasticity and raised the storage modulus G' from 0.11 to 5.95 Pa. The 20/40 mesh ceramsite proppant remained suspended in the LMPS solution (36 mPa·s) for 30 min, whereas ceramsite completely settled within 30 s in an ordinary linear polymer solution with similar viscosity. Simultaneously, despite having a lower molecular weight, the drag reduction rate test shows that the drag reduction performance of the LMPS fracturing fluid was similar to the tested conventional commercial linear polymer. The self-assembled network of HAWSP/surfactant can increase the viscoelasticity of the fracturing fluid, which is expected to overcome the weakness of insufficient proppant transport capacity of slick water, thus improving development efficiency of unconventional gas reservoirs.

Preparation and properties research of a bifunctional hydrophobic associative polymer drag reduction agent for slick water

AbstractIn this study, the bifunctional hydrophobic associative polymer of Acrylamide/2‐Acrylamido‐2‐Methylpropane Sulfonic Acid/Lauryl Methacrylate/N,N‐dodecyl Acrylamide (AALD12) with better salt resistance and shear resistance was synthesized by free‐radical micelle polymerization for use as a drag reduction in shale slip water fracturing. In deionized water, the critical associative concentration (CAC) of AALD12 was 0.23%. AALD12 was determined to be theoretically usable for a shale reservoir within 240°C based on its TG study. Microstructure, viscoelasticity, and shear recovery tests show that the polymer has good drag reduction potential and shear resistance. The reduction rates of the polymer AALD12 and the drag reduction agent RSH‐1 in clear water were 77% and 73% (RSH‐1 is a commonly used emulsion‐type drag reduction agent in the market). At the same salt concentration (K+ and Ca2+, 50,000 ppm) and flow rate (40 L/min), AALD12 can maintain a maximum reduction rate of about 63%. The drag reduction rate of RSH‐1 in K+ and Ca2+ solutions can only be maintained at about 52% and 28%, respectively. In the shear resistance test, AALD12 and RSH‐1 were each subjected to three times of cyclic shear in the test pipe. The drag reduction rate of the polymer AALD12 solution can still reach more than 72%. The drag reduction rate of the RSH‐1 solution is about 56%. The drag reduction agent has good salt resistance and anti‐shear bifunction.

Synthesis of a novel double-tailed hydrophobically associating polymer for ultra-high salinity resistance

A new strategy for preparing double-tailed hydrophobic monomer, N, N-diethyldodecanamide methacrylamide (DEDAMA), was designed. Then, the synthesized monomer was used to prepare the hydrophobic associated polymer (PAM/AA/DEDAMA) to improve salt resistance under ultra-high salinity conditions. Viscosity and rheological behavior were evaluated. The results showed that the viscosity of the polymer in saline water was higher than that in fresh water, indicating an evident salt thickening ability. An obvious shear thickening phenomenon was observed in rheological experiments, showing strong interactions among the polymer chains. We attributed the observed properties to the unbroken hydration shell and spatial network, which can be observed in the scanning electron microscopy images. Based on these properties, the polymer can be used to improve proppant suspension ability and foam stability at ultra-high salinity, indicating its potential for application in the petroleum industry.

Experimental Study on Phenol-Formaldehyde Resin Aggregates as In-Depth Conformance Control Agents Stabilized by Polymer.

To improve the dispersion stability of phenol-formaldehyde resin (PFR) particles in simulated oilfield injection water and their propagation ability in petroleum reservoir, a hydrophobically associating polymer (HAP) was employed as a stabilizer in this paper. The dispersion stability of PFR in the injection water was studied by measuring turbidity as a function of time. In addition, the migration property of the PFR/HAP dispersion was evaluated by both cellulose membrane filtration and sand packs-flooding experiments. The results show that HAP can stabilize the PFR dispersion prepared with the simulated injection water by forming PFR/HAP complex molecular aggregates. These aggregates can migrate in sand packs with strong flow resistance due to deformation or disaggregation of the aggregates when passing through the pore throat. Oil recovery was improved by up to 21.1% on the basis of water flooding, and the higher the concentration of PFR/HAP dispersion system, the better the oil recovery effect. Moreover, the cycle of log-jamming/dispersion of the aggregates leads to their penetrations through the bigger pores in the sand packs with a higher flow resistance than water. This process can improve the conformance of water in high permeability sand packs on a micro/macro scale and thus divert more water into low permeability sand packs. Therefore, more oil could be recovered from the low permeability sand packs. Moreover, the bigger the sand pack’s permeability ratio, the lower the oil recovery rate by waterflood, and the more the incremental oil can be recovered by the PFR/HAP flood.

Design of salt-responsive low-viscosity and high-elasticity hydrophobic association polymers and study of association structure changes under high-salt conditions

A hydrophobic associative water-soluble polymer, SRHV, was designed and synthesized in this study. The CAC of SRHV was 0.072 wt% and 0.2 wt%. The scanning electron microscopy tests showed that the polymer demonstrated a multilayer network structure. Rheological tests revealed that polymer solution exhibited low-viscosity and high-elasticity rheological behaviors under high-salinity conditions and this salt-responsive behavior persists at high temperatures. Fluorescent probe tests confirmed that salt addition promoted the formation of hydrophobic association networks. Through molecular dynamics simulation, various parameters, such as mean square displacement (MSD), radius of gyration (Rg), and radial distribution function (RDF), were analyzed to further explain the salt-tolerance mechanism of SRHV and the effect of salt ions on the hydrophobic association structure. The results showed that the viscosity and elasticity of polymers were not necessarily correlated. In addition, elasticity dominated when the positive effect of salt-promoted association exceeded the negative effect of salt-coiled molecular chains and polymer relies on elasticity to achieve an excellent sand-carrying effect at this time. In general, SRHV exhibits great potential for application in oil fields with high salt environment, which could effectively reduce the waste of freshwater resources. Furthermore, this work provides some support for suspending sand relying on elastic.

Application and Optimization of the Rheological Model for a Hydrophobically Associating Dendrimer Polymer.

Polymer flooding is one of the most important enhancing oil recovery (EOR) technologies in the world. With the optimization of polymer synthesis, the performance of polymer solutions has been greatly improved, which can adapt to more complex oil and gas reservoirs. However, with the continuous improvement of the properties of polymer solutions, the elastic property of polymer solutions is significantly improved, and the rheological law has also changed. This series of changes affects the application of polymer flooding reservoir numerical simulation technology. Therefore, constructing an accurate description model and precise limitation conditions is particularly important. The rheological curve with a wide shear range (0.1~10,000 s−1) and the viscoelasticity of the two polymers (partially hydrolysed polyacrylamide (HPAM) and dendritic hydrophobic association polymer (DHAP)) were analyzed and tested by a rotating rheometer. The results showed that under the experimental conditions, the rheological curve of both polymers can be described by the Carreau rheological model. Meanwhile, the structural viscosity of the hydrophobically associating polymer solution (DHAP) greatly improved the elasticity of the solution and led to the change of elastic modulus. Considering the influence of elastic characteristics on the rheological curve, the relaxation time spectrum derived from small vibration experimental data was used to limit the characteristic relaxation time, that is, the value range of λ. It was observed that the experimental data were highly matched with the nonlinear regression fitting curve of the Carreau rheological model. Therefore, the relationship between different test parameters should be fully considered while studying the rheological constitutive equation of viscoelastic fluid, so as to optimize and improve the equation of it.

Hydrophobically Associating Polymers Dissolved in Seawater for Enhanced Oil Recovery of Bohai Offshore Oilfields.

As compared to China’s overall oil reserves, the reserve share of offshore oilfields is rather significant. However, offshore oilfield circumstances for enhanced oil recovery (EOR) include not just severe temperatures and salinity, but also restricted space on offshore platforms. This harsh oil production environment requires polymers with relatively strong salt resistance, solubility, thickening ability, rapid, superior injection capabilities, and anti-shearing ability. As a result, research into polymers with high viscosity and quick solubility is recognized as critical to meeting the criteria of polymer flooding in offshore oil reservoirs. For the above purposes, a novel hydrophobically associating polymer (HAP) was prepared to be used for polymer flooding of Bohai offshore oilfields. The synthetic procedure was free radical polymerization in aqueous solutions starting at 0 °C, using acrylamide (AM), acrylic acid (AA), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), and poly(ethylene glycol) octadecyl methacrylate (POM) as comonomers. It was discovered that under ideal conditions, the molecular weight of HAP exceeds 2.1 × 107 g⋅mol−1. In a simulated reservoir environment, HAP has substantially greater solubility, thickening property, and salt resistance than conventional polyacrylamide (HPAM), with equivalent molecular weight. Finally, the injectivity and propagation of the two polymers in porous media were investigated. Compared with HPAM, which has a similar molecular weight, HAP solution with the concentration of 0.175% had a much better oil displacement effect in the porous medium, which can enhance oil recovery by 8.8%. These discoveries have the potential to pave the way for chemical EOR in offshore oilfields.

Evaluation of temperature resistance of non chemical crosslinked double-tailed hydrophobically associating polymer fracturing fluid

The global spread of COVID-19 continues, industrial raw material production is being tested, and the fracturing cost of oil and gas fields continues to rise, posing new challenges to polymer fracturing fluids. A new hydrophobic association polymer PDMA1 with a double tailed monomer structure was synthesized inside this study. Fourier infrared spectroscopy, Electron microscope scanning, Fluorescence spectroscopy, and polymer viscoelasticity were used to investigate the polymer's basic properties. Finally, using molecular dynamics simulation tools, the network structure of PDMA1 was discovered to be more temperature resistant than that of HPAM. PDMA1 has larger hydrodynamic dimensions than HPAM at the same temperature, its radius of gyration is more than HPAM, and its viscosity is greater than HPAM under the same conditions. This provides an additional avenue of investigation for temperature-resistant hydrophobically associating polymers.

The injection method of a hydrophobic associated polymer with evident salt thickening property

A comb like micro-blocked hydrophobic association polymer (CBHAP) with evident thickening property in high salinity and weak thickening property in fresh water was developed. Based on the unique property, we designed the injection strategy that polymer in fresh water with low viscosity was injected into the cores to improve injectivity and high salinity water was used to perform subsequent water flooding to improve mobility control ability. The factors influencing on the injectivity as well as mobility control ability were researched by the core flooding experiments. As a result, pressure fluctuation was found in the subsequent water flooding from 0.7 PV to 1.5 PV, showing obvious variation of viscosity in the cores. The phenomenon was believed to improve mobility control ability. In addition, the positive correlation between polymer concentration, salinity, injected volume and the fluctuation was found. The designed injection method for the polymer can be used to solve injectivity issue as well as improve mobility control ability in high salinity reservoir.

Synthesis of a hydrophobic association polymer with an inner salt structure for fracture fluid with ultra-high-salinity water

This study used a compound initiation free radical polymerization process to synthesize a hydrophobic association polymer (PDMA1) with good salt resistance for use in ultra-high salinity reservoirs. The critical association and entanglement concentrations of PDMA1 in deionized (DI) water were 1596 and 2799 mg/L, respectively. The properties of the polymer in simulated formation (SF) water were investigated using viscosity change and conductivity tests, and the apparent viscosity of the PDMA1 solution was investigated using apparent viscosity, viscoelasticity, and thixotropy experiments. To a certain extent, the apparent viscosity of the solution was found to be influenced by metal ions. Under total dissolved solids (TDS) concentrations of up to 239,500 ppm, when the polymer concentration exceeded the critical entanglement concentration, the apparent viscosity of the polymer remained close to that of DI water. Additionally, the viscosity of the PDMA1 solution was affected by different types of metal ions, and the polymer solution thickened owing to divalent cations. PDMA1 is resistant to salt owing to hydrophobic interaction, electrostatic shielding, and double-layer compression. The results of the thixotropy and viscoelasticity tests revealed the thixotropy loop area of the PDMA1 solution in SF water to be greater than that in DI water. Under these conditions, PDMA1 is mostly viscous at low shear frequencies and mostly elastic at high shear frequencies. The PDMA1 inner-salt hydrophobic association polymer can be utilized as a chemical agent for tertiary recovery and fracturing, processes in high-salinity reservoirs, particularly for aggravating fracturing fluid.