Cross-linked Polymer Gels Research Articles

Preparation and properties of new green polyacrylamide hydrogels

Abstract The pursuit of low-toxicity hydrogels represents a focal point and frontier in contemporary research endeavors. Partially hydrolyzed polyacrylamide emerges as the most prevalent polymer employed in the formulation of priority flow control gels, owing to its favorable cost-efficiency and heightened receptivity to crosslinking agents. A noteworthy discovery pertains to the utilization of a green crosslinking agent derived from TiSO4, which induces the gelation of polyacrylamide, resulting in an elevation of apparent viscosity from 1159 mPa·s to 100, 000 mPa·s. Extensive investigations into the primary factors influencing the performance of crosslinked polymer gels and their underlying principles have been conducted. The advent of such gel plugging agents holds promise in addressing challenges encountered in select reservoir scenarios, thereby furnishing reliable technical underpinnings for the efficacious stimulation of oil fields.

Valence fixable ferrozine gel rod combined with smartphone for facile determination of redox-active Fe2+ in environmental water

Ferrous ion (Fe2+) can indicate the redox situation of water and also plays an important role in maintaining the ecological balance of water bodies. However, due to the redox-active property of Fe2+, it is still a huge challenge to sensitively and accurately determine Fe2+ especially in interstitial water. Herein, we prepared a ferrozine gel rod for valence fixation during sampling and subsequent smartphone-based detection of Fe2+. The electrode potential of the redox pair can be varied through the formation of Fe2+-ligand complexes, and when Ecomplex was higher than EO2/OH−, the oxidation of Fe2+ by O2 was hindered, thus achieving the valence fixation of Fe2+. Six ligands were screened, and it was found that ferrozine could effectively increase the redox potential after complexing with Fe2+, and also exhibits an obvious color change while fixing the valence of Fe2+. To facilitate Fe2+ detection, a cross-linked porous polymer gel rod prepared by acrylamide and sodium alginate was used to encapsulate the ferrozine molecules. The ferrozine gel rod enabled fixation the valence of Fe2+ longer than 30 days, and the resulted purple-red color was pictured and analyzed by a smartphone. Ultimately, the developed ferrozine gel rod sensing system was able to achieve sensitive and linear detection of Fe2+ in the range of 1–200 μM with the limit of detection as low as 0.33 μM, and it also exhibited excellent selectivity and anti-interference ability. The accuracy and reliability of the method was verified by the determination of Fe2+ in spiked water samples and certified standard reference water samples. Finally, the ferrozine gel rod sensing system was successfully applied to in-situ detection of Fe2+ in interstitial water, overlying water and upper water of lake and river. This facile system that enabled valence fixation and fast detection is promising for detection of Fe2+ in environmental waters.

Performance evaluation and physical simulation experiment of SiO2 nanoparticle synergistic crosslinked polymer system

Abstract As natural gas development gradually shifts from early to mid to late stages, water outflow from gas wells has become an inevitable problem. In this study, polyethyleneimine cross-linked polymers were synthesized and nano particles were introduced to obtain SiO2 nanoparticle synergistic cross-linked polymer systems. Rheological experiments show that the system has stronger shear resistance and higher yield stress, and the linear viscoelastic region has a stress amplitude less than 3.5Pa, exhibiting good elastic properties in the range of 0.01 to 10Hz. In terms of stability, after 45 days of aging, the viscosity retention rate of the system is 77.66%. When the mineralization degree is 224852mg/L, the viscosity retention rate is greater than 76.33%, indicating that the system has good aging stability and salt resistance.The physical simulation experiment of core displacement shows that SiO2 nanoparticle synergistic cross-linked polymer gel has gas-water selective plugging ability, and the reduction of water phase permeability is much greater than that of gas phase. The gas phase permeability can remains at about 75%, which is 2300 times that of water phase permeability, and has a good water plugging effect.

Shallow penetration conformance sealants (SPCS) based on organically cross-linked polymer and particle gels—An overview

Shallow penetration conformance sealants (SPCS) based on organically cross-linked polymer and particle gels—An overview

Photopatterned Hybrid Supramolecular/Polymer Hydrogels for Controlled Heparin Release and Stem Cell Growth

AbstractThis paper reports hybrid gels combining a low‐molecular‐weight gelator (LMWG) and a photoinitiated crosslinked polymer gel (PG). The presence of the PG enhanced the stiffness and strength of the gel. The gels were loaded with heparin, and in the hybrid gel, the interpenetrated LMWG and PG networks somewhat restricted its release. In terms of stem cell growth, the hybrid gel significantly improved the performance of the PG because of the presence of the LMWG, which is an excellent substrate for stem cells in its own right. Furthermore, the presence of heparin in the hybrid gels also enhanced stem cell proliferation over longer timescales. Finally, these gels were photopatterned within the well‐plates used for tissue culture, with patterning helping control stem cell proliferation. In summary, these hybrid gels combine the advantageous features of both LMWG and PG: rheological performance is endowed by the PG with stem cell compatibility provided by the LMWG. The hybrid gels also control the release of the bioactive agent heparin and have capacity to be shaped and patterned. Patterned gels such as these, capable of directing stem cell growth, have potential in regenerative medicine.

Lattice Boltzmann simulation of cross-linked polymer gel injection in porous media

This study addresses the critical challenge of excessive water production in mature oil and gas reservoirs. It focuses on the effectiveness of polymer gel injection into porous media as a solution, with an emphasis on understanding its impact at the pore scale. A step-wise Lattice Boltzmann Method (LBM) is employed to simulate polymer gel injection into a 2D Berea sample, representing a realistic porous media. The non-Newtonian, time-dependent characteristics of polymer gel fluid necessitate this detailed pore-scale analysis. Validation of the simulation results is conducted at each procedural step. The study reveals that the methodology is successful in predicting the effect of polymer gel on reducing permeability as the gel was mainly formed in relatively larger pores, as it is desirable for controlling water cut. Mathematical model presented in this study accurately predicts permeability reductions up to 100% (complete blockage). In addition, simulations conducted over a wide range of gelation parameters, TD_factor from 1 to 1.14 and Threshold between 0.55 and 0.95, revealed a quadratic relationship between permeability reduction and these parameters. The result of this research indicates LBM can be considered as promising tool for investigating time-dependant fluids on porous media.

Multistep pH-peak-focusing liquid chromatography with a hydrophilic polymer gel column for separation of rare earth elements

Multistep pH-peak-focusing liquid chromatography with a column packed with a hydrophilic polymer gel (a cross-linked hydroxylated methacrylic polymer gel) was developed for separation of rare earth metal ions. Metal ions in a sample solution introduced to the column are chromatographically extracted into the stationary gel phase at the top of the column equilibrated with a basic solution used as the first mobile phase containing acetylacetone and 1,10-phenanthroline by synergistic extraction effect. After the sample solution is introduced, the mobile phases are delivered into the column by stepwise gradient elution in order of decreasing pH. Each metal ion is concentrated at a pH border formed between the zones of different pH in the column and moves toward the outlet of the column with the pH border. Mutual separation of La(III), Ce(III), Nd(III), Eu(III), Y(III), Tb(III), and Yb(III) was achieved by the present method for an 1-mL sample injection with the column of which the inner volume is 11.8 mL. The multistep pH-peak-focusing liquid chromatography with a hydrophilic polymer gel column developed in this study has great potential as a useful method for the separation of rare earth metal ions on a preparatory scale.

Design of Artificial Neural Network for predicting the reduction in permeability of porous media as a result of polymer gel injection

Cross-linked polymer gel is widely used in the oil and gas industry to block high permeability conduits and reduce water cut. The complex nature of this fluid, especially regarding flow in porous media, makes its numerical simulation very time-consuming. This study presents an approach to designing an Artificial Neural Network (ANN) model that could predict the permeability reduction caused by injecting polymer gel into a 2D rock sample. Our methodology consists of two main parts: numerical simulation and ANN model building. Considering the advantages of the Lattice Boltzmann Method (LBM) this approach is used to model the injection of polymer gel in porous media. Using this model, more than 20,000 simulations were performed which resulted in highly unbalanced dataset, so an innovative approach for balancing regression dataset is also proposed in detail in this paper. The final constructed ANN model could predict the permeability reduction in a fraction of a second with less than 2.5% Mean Absolute Error (MAE). The result indicates the importance of balancing datasets to obtain a reliable prediction from ANN. Also, it should be mentioned that gelation parameters had the most significant impact on the value of permeability reduction, with mean absolute SHapley Additive exPlanations (SHAP) values of 20 and 12.5 for TDfactor and Threshold, respectively.

Study on migration and plugging performance of polymer gel in fractured cores using nuclear magnetic resonance technology

In situ cross-linked polymer gels (ISCPGs) are widely used for conformance control and enhanced oil recovery (EOR) in heterogeneous petroleum reservoirs. However, the mechanisms behind their migration and plugging in fractured cores remain unclear. In this study, changes in the injection pressure difference before and after the treatment of HPAM/phenolic resin gel was monitored by core displacement experiment. The gel was injected with two different gelation states, i.e., gelant and pre-crosslinked gel. Meanwhile, we analyzed the nuclear magnetic resonance (NMR) T2 signal and imaging of the cores that were treated with the polymer gel system during various injection stages. Results indicated that NMR technology can effectively analyze the migration and plugging performance of polymer gels in fractured cores at a microscopic level, both before and after gelation. The gelant effectively plugged the fracture when the injection rate was low, but a great amount of the gelant entered the matrix and damaged the matrix. In contrast, it formed a plugging layer at the inlet face and also caused damage at high injection rates. For conformance treatment of pre-crosslinked gels, the gel did not easily enter the matrix. When the injection rate of pre-crosslinked gels increased, its plugging efficiency for the fractured cores enhanced. Therefore, engineers should optimize gel state, injection rate, and injection pressure according to the specific reservoir conditions before oilfield operations. This study can help researchers understand the microscopic migration and plugging mechanism of polymer gels in cores at the microscopic level. It will also help researchers to pay more attention to the NMR technique to further understand its application in petroleum reservoir conformance improvement.

Biodegradable Preformed Particle Gel (PPG) Made of Natural Chitosan Material for Water Shut-Off Application.

Oil and gas extraction frequently produces substantial volumes of produced water, leading to several mechanical and environmental issues. Several methods have been applied over decades, including chemical processes such as in-situ crosslinked polymer gel and preformed particle gel, which are the most effective nowadays. This study developed a green and biodegradable PPG made of PAM and chitosan as a blocking agent for water shutoff, which will contribute to combating the toxicity of several commercially used PPGs. The applicability of chitosan to act as a crosslinker has been confirmed by FTIR spectroscopy and observed by scanning electron microscopy. Extensive swelling capacity measurements and rheological experiments were performed to examine the optimal formulation of PAM/Cs based on several PAM and chitosan concentrations and the effects of typical reservoir conditions, such as salinity, temperature, and pH. The optimum concentrations of PAM with 0.5 wt% chitosan were between 5-9 wt%, while the optimum chitosan amount with 6.5 wt% PAM was in the 0.25-0.5 wt% range, as these concentrations can produce PPGs with high swellability and sufficient strength. The swelling capacity of PAM/Cs is lower in high saline water (HSW) with a TDS of 67.2976 g/L compared with fresh water, which is related to the osmotic pressure gradient between the swelling medium and the PPG. The swelling capacity in freshwater was up to 80.37 g/g, while it is 18.73 g/g in HSW. The storage moduli were higher in HSW than freshwater, with ranges of 1695-5000 Pa and 2053-5989 Pa, respectively. The storage modulus of PAM/Cs samples was higher in a neutral medium (pH = 6), where the fluctuation behavior in different pH conditions is related to electrostatic repulsions and hydrogen bond formation. The increase in swelling capacity caused by the progressive increment in temperature is associated with the amide group's hydrolysis to carboxylate groups. The sizes of the swollen particles are controllable since they are designed to be 0.63-1.62 mm in DIW and 0.86-1.00 mm in HSW. PAM/Cs showed promising swelling and rheological characteristics while demonstrating long-term thermal and hydrolytic stability in high-temperature and high-salinity conditions.

Investigating the performance of non-damaging hybrid gel to mitigate lost circulation in fractured formations: A comprehensive study using Box–Behnken design

Gels that have a low viscosity at the time of mixing and form a three-dimensional gel structure after some time delay can be applied successfully in controlling lost circulation. Cross-linked gels play an important role in sealing high permeable and fractured formations. This research aims to evaluate a novel gel that can mitigate lost circulation during drilling in fractured formations. The hybrid gel consists of a cross-linked polymer gel as the continuous phase and an oil as the internal phase. The purpose of designing hybrid gels is to reduce the possibility of formation damage caused by the presence of gel in the fractures. In addition, the use of an internal phase in the gel can increase the durability of the gel and reduce the final cost of the operation.This article consists of two parts, experimental investigation and empirical modeling using response surface methodology. A number of parameters such as initial gelation time, final gelation time, and cross-linking rate were defined to evaluate the gel behavior under different conditions. First, the effect of polymer type, internal phase viscosity, pH, temperature, salinity, and shear rate on the behavior of the hybrid gel was investigated. Furthermore, in order to increase cross-linking efficiency, the cross-linker was added onto the reactive nano-silica surface to achieve a nano-crosslinker, and then the performance evaluation was accomplished. Thereafter, the sealing pressure test was examined to measure the amount of pressure that the hybrid gels could withstand in the fractures to prevent further fluid loss. Finally, the amount of gel rupture in 15% and 28% hydrochloric (HCl) was studied over time at 25 and 60 °C so as to evaluate the formation damage of hybrid gels.Response surface methodology (RSM) was employed based on Box-Behnken design to determine a correlation for predicting the final viscosity of hybrid gel as a function of temperature, pH, and CaCl2 concentration. The predicted model was obtained by solving the quadratic regression model. The value of the correlation coefficient (R2 = 0.90) for the present mathematical model indicated good relation between experimental data and predicted values. Therefore, the proposed model is able to predict the final viscosity of hybrid gel adequately within the limits of input parameters being used.The experimental results show that hybrid gels, due to their flexible viscosity response, long-term stability, and non-damaging properties, can have proper performance and application in industry to combat lost circulation. Nano-crosslinker can effectively increase the cross-linking rate and final viscosity of the gel and also improve the gel performance at high temperatures. Based on dynamic sealing pressure experiments, the value of maximum sealing pressure for the guar-based hybrid gel is higher than that of xanthan. In addition, the nano-crosslinker enhances the maximum tolerable pressure of the gels to seal the fractures.

Chain-Extendable Crosslinked Hydrogels Using Branching RAFT Modification.

Functional crosslinked hydrogels were prepared from 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA). The acid monomer was incorporated both via copolymerization and chain extension of a branching, reversible addition-fragmentation chain-transfer agent incorporated into the crosslinked polymer gel. The hydrogels were intolerant to high levels of acidic copolymerization as the acrylic acid weakened the ethylene glycol dimethacrylate (EGDMA) crosslinked network. Hydrogels made from HEMA, EGDMA and a branching RAFT agent provide the network with loose-chain end functionality that can be retained for subsequent chain extension. Traditional methods of surface functionalization have the downside of potentially creating a high volume of homopolymerization in the solution. Branching RAFT comonomers act as versatile anchor sites by which additional polymerization chain extension reactions can be carried out. Acrylic acid grafted onto HEMA-EGDMA hydrogels showed higher mechanical strength than the equivalent statistical copolymer networks and was shown to have functionality as an electrostatic binder of cationic flocculants.

Expansion microscopy through mechanical force.

In biophysics interesting phenomena take place during the interaction between biological molecules on the order of nanometers. Optical super-resolution imaging techniques surpass the diffraction limit of light enabling higher resolutions to study these phenomenon. However, super-resolution techniques usually require expensive equipment. Expansion microscopy (ExM) is a sample preparation method that facilitates super-resolution imaging by leveraging osmotic forces to physically separate features smaller than the diffraction limit of light. ExM is cheaper than and compatible with other super-resolution methods to reach the nanoscale. Currently, ExM commonly produces 4.5X linear expansion and 20X has been achieved using successive expansion steps, but this can result in fragmentation of the biological sample. Allowing the gel to absorb water to expand is also as low process. To overcome the fragmentation and time issues, here, we use a highly stretchable cross-linked polymer gel and a mechanical stretcher device to achieve similar 20X linear expansion in minutes. Since we do not rely on osmotic forces for the expansion, this method is more compatible with other techniques which are incompatible with excess water. We demonstrate our expansion microscopy method by imaging MOSE cells at 50 nm resolution. We establish mechanical force expansion microscopy as a viable sample preparation method with the same advantages as ExM while being much faster. This will also allow researchers to study time sensitive phenomenon.

Multistep sequence-controlled supramolecular polymerization by the combination of multiple self-assembly motifs

The precise sequence control of polymer chain is an important research topic of polymer chemistry. Although some methods such as iterative synthesis and supramolecular polymerization have been developed to fabricate sequence-controllable polymer, it is still a great challenge to consecutively prepare multiple supramolecular polymers with different sequence structures. In this work, through the reasonable utilization of assembly motifs, we integrated multiple host-guest recognitions and metal coordination interactions to prepare different sequence-controlled supramolecular polymers by a multistep assembly strategy. This research provides inspiration for the design and preparation of supramolecular polymers with different sequence structures.

Hydrogen generation from NaBH4 hydrolysis catalyzed by cobalt (0)-Deposited cross-linked polymer brushes: Optimization with an experimental design approach

Proposing a novel catalyst that achieves catalytic hydrolysis of metal hydrides is an important stage in developing a hydrogen storage system. In this study, a cross-linked gel brush-cobalt (0) composite (Co@P4VPGB@PMC) has been synthesized to obtain hydrogen from NaBH4 solution. The morphology, structure, and composition of the obtained catalyst have been characterized by, FTIR, SEM, EDX, BET, XRD, ICP-MS and XPS. The parameters that significantly affect the hydrolysis of NaBH4 (such as NaBH4 concentration, NaOH amount, catalyst amount, and temperature) have been investigated using response surface methodology (RSM), an optimization method that has gained increasing importance in recent years. The hydrogen generation rate (HGR) was 4499 mL/min gcat for Co@P4VPGB@PMC when the NaBH4 amount was 241.52 mM, NaOH amount 5 wt%, catalyst amount 10.55 mg and temperature 58.9 °C. Moreover, the apparent activation energy (Ea) for the catalytic hydrolysis reaction has been 41.27 kJmol-1 obtained under optimum conditions. Additionally, the Co@P4VPGB@PMC catalyst displayed significant reusability performance for up to five cycles without major loss of its activity. Compared with metal catalysts, this new cross-linked polymer gel brush-cobalt catalyst has excellent potential applications for hydrogen production by hydrolysis of metal hydrides due to its simple synthesis, low cost, and the easy availability of raw materials.

Evaluation of novel organically crosslinked polymer gel for water shut-off purposes

One common issue faced in the lifespan of oil or gas wells is water-cut, which leads to economic challenges due to water handling and operational costs, as well as reduced oil productivity. In this study, an organically cross-linked system consisting of HQ/HMTA is used for experimental work, as a substitute for the phenol/formaldehyde system with lower toxicity levels. The present study focuses on bulk gelation studies using the bottle testing method with polymer gelant prepared from PAM and HQ/HMTA. Determining the gelation time at different temperatures is important to understand the depth up to which the gel can be placed in the formation at reservoir temperature. The study revealed that gelation time can be controlled by adjusting gel composition and environmental conditions, ranging from a few hours to several days; higher polymer and crosslinker concentration in the gelant solution results in decreased gelation time, but excessive cross-linking leads to syneresis beyond a certain range; Gelation occurs more rapidly in the presence of low concentration salt compared to distilled water, but when brine concentration is increased, the gelation time increases due to the screening effect and reduced availability of cross-linking agents; Divalent ions tend to promote faster gelation compared to monovalent ions, likely due to their higher charge density. Overall, presented gel system is highly efficient in shutting off water in reservoirs. Keywords: water shut-off; organically crosslinked gel; gelation time; resistance factor; residual resistance factor; divalent ions.

Importance of conformance control in reinforcing synergy of CO2 EOR and sequestration

Injecting CO 2 into hydrocarbon reservoirs can enhance the recovery of hydrocarbon resources, and simultaneously, CO 2 can be stored in the reservoirs, reducing considerable amount of carbon emissions in the atmosphere. However, injected CO 2 tends to go through fractures, high-permeability channels and streaks present in reservoirs, resulting in inefficient hydrocarbon recovery coupled with low CO 2 storage performance. Conformance treatments with CO 2 -resistant crosslinked polymer gels were performed in this study to mitigate the CO 2 channeling issue and promote the synergy between enhanced oil recovery (EOR) and subsurface sequestration of CO 2 . Based on a typical low-permeability CO 2 -flooding reservoir in China, studies were performed to investigate the EOR and CO 2 storage performance with and without conformance treatment. The effect of permeability contrast between the channels and reservoir matrices, treatment size, and plugging strength on the efficiency of oil recovery and CO 2 storage was systematically investigated. The results indicated that after conformance treatments, the CO 2 channeling problem was mitigated during CO 2 flooding and storage. The injected CO 2 was more effectively utilized to recover the hydrocarbons, and entered wider spectrum of pore spaces. Consequently, more CO 2 was trapped underground. Pronounced factors on the synergy of EOR and CO 2 storage were figured out. Compared with the treatment size, the CO 2 storage efficiency was more sensitive to the plugging strength of the conformance treatment materials. This observation was important for conformance treatment design in CCUS-EOR projects. According to this study, the materials should reduce the channel permeability to make the channel/matrix permeability ratio below 30. The results demonstrate the importance of conformance treatment in maximizing the performance of CCUS-EOR process to achieve both oil recovery improvement and efficient carbon storage. This study provides guidelines for successful field applications of CO 2 transport control in CO 2 geo-utilization and storage.

Development of re-crosslinkable dispersed particle gels for conformance improvement in extremely high-temperature reservoirs

Micro-scale and nano-scale dispersed gel particles (DPG) are capable of deep migration in oil reservoirs due to their deformability, viscoelasticity, and suitable particle size. Therefore, it has been widely studied and applied in reservoir conformance control in recent years. However, for highly permeable channels, their plugging performance is still limited. In addition, conventional in situ cross-linked polymer gels (ISCPGs) have fast gelation time under extremely high-temperature conditions, which often causes problems such as difficulty in pumping. Therefore, a re-crosslinkable dispersed particle gel (RDPG) system applied for conformance control in highly permeable channels of extremely high-temperature petroleum reservoirs was investigated. The particle size distribution, gelation time, gel strength, injection performance, and performance strength in porous media were investigated using a laser particle size meter, the Sydansk bottle test method, rheometer, and core displacement experiments, respectively. Results show that the RDPG suspension can be stable for more than 6 months at room temperature with storage modulus G ′ much lower than 10 Pa. It can pass through the pore throat by elastic deformation effect and does not cause strong blockage. Moreover, it can undergo re-crosslinking reaction at 150 °C to form a strong bulk gel. The gel strength G ′ of re-crosslinked RDPG can be as high as 69.3 Pa, which meets the strength requirement of conformance control. The RDPG suspension has the properties of easy injection, and it also has strong plugging, and high-temperature resistance after re-crosslinked in the core, which can be a very promising material for conformance improvement in extremely high-temperature reservoirs.

Controlled gel expansion through colloid oscillation.

We model the behavior of a single colloid embedded in a cross-linked polymer gel, immersed in a viscous background fluid. External fields actuate the particle into a periodic motion, which deforms the embedding matrix and creates a local microcavity, containing the particle and any free volume created by its motion. This cavity exists only as long as the particle is actuated and, when present, reduces the local density of the material, leading to swelling. We show that the model exhibits rich resonance features, but is overall characterized by clear scaling laws at low and high driving frequencies, and a pronounced resonance at intermediate frequencies. Our model predictions suggest that both the magnitude and position of the resonance can be varied by varying the material's elastic modulus or cross-linking density, whereas the local viscosity primarily has a dampening effect. Our work implies appreciable free-volume generation is possible by dispersing a collection of colloids in the medium, even at the level of a simple superposition approximation.

Overview of In-Situ Gelation Behavior of Gel Systems in Porous Media

Cross-linked polymer gel has been widely applied in profile control and water plugging due to its effective cost, wide suitability, excellent performance, and flexible gelation time. Previous research mainly focused on the bottle tests, reaction kinetics, and rheological properties of the gels, but the works of literature about the in situ gelations of gel placement in the porous media are relatively few. The study of the in-situ gelation behavior of gel systems is widely summarized in this paper, and the research tendency is proposed. The important practical questions, including the accurate lateral distance of gel placement, the variation of gel properties, and the injection pressure profile in the process of gel injection, should be resolved by laboratory and numerical research to enhance gel treatment success rate.