Polymer Gel Systems Research Articles

Engineering water-shut-off operations: Application of rheological time-temperature superposition approach for organically-crosslinked polymer gel systems

Polymer-based gels have been extensively utilized in reservoirs to prevent excessive water production and improve oil recovery. In this study, a sulfonated-hydrolyzed polyacrylamide polymer (HPAM-S) and low-toxic organic crosslinkers (hydroquinone and hexamethylenetetramine) were mixed in brine at specified concentrations to formulate the polymer-crosslinker fluid system. The quantitative rheological analysis, along with the TTS (Time-Temperature Superposition) approach, was examined for the first time to achieve the water shut-off operations in high-temperature reservoirs (90 °C–150 °C). The TTS approach was defined as modelling of the viscosity vs. time data obtained at various temperatures using an appropriate empirical shift factor (at) such that a single master curve is established for the viscosity evolution of the given fluid system. This approach facilitates the prediction of the gelation behavior of polymer-crosslinker fluid systems as a function of time at varied reservoir temperatures especially over time scales that are not experimentally accessible. The time-dependent rheological evolution of the fluid system was experimentally investigated using batch-wise bottle testing methods as well as viscosity and viscoelastic measurements by employing an advanced rheometer. The TTS approach was applied to the obtained rheological data at varied temperatures. The model was validated for an unknown set of temperature vs. viscosity data. Based on the TTS approach, the term ‘gelation time’ was defined as the time required to reach a pre-specified viscosity to signify a transition from the liquid-like state to the solid-like state. The gelation time decreases with increasing temperatures. After the gelation time, at each temperature, a swift increase in the fluid viscosity was observed, indicating the initiation of the rapid crosslinking in the fluid systems. It was found that beyond the gelation time, the batch-wise bottle testing showed (G-I) gel strength (qualitative). Analogously, the visco-elasticity test demonstrated a rapid rise in elastic modulus (G′) beyond the gelation time. An underlying mechanism based on polymer hydrolysis was utilized to explain the evolution of distinct viscous and viscoelastic properties as a function of temperature. Moreover, the modeling predictions for the fluid systems were examined for in-situ rock plugging with the help of core-flood equipment. The core-flooding tests confirmed a 99% reduction in the rock permeability beyond the gelation time. The gelation time values obtained from both the batch-wise bottle testing method and rheological tests for the polymer-crosslinker fluid systems were found in agreement with each other, with a tolerance of (±5%).

Visualization of the Characteristics of Polymer Gel Plugging of Fracture in the Multi-Slug Process

Abstract Polymer gel is a promising system for conformance control and water shutoff in water flooding reservoirs. However, the presence of fractures in reservoirs poses a major challenge to the successful application of polymer gels. This is because direct visualization of polymer gel system flow in the fracture is still lacking. In this paper, the HPAM/CrAc gel system was used to study the transport and plugging characteristics of gel multi-slug plugging using a visualized fracture model. The experimental results showed that multi-slug plugging accompanied by gradual compaction significantly improved the blocking strength of the polymer gel within the fracture. Specifically, multi-slug plugging improves the pressure gradient of the chasing water by approximately 80-200 kPa/m compared to one-step plugging of the polymer gel. During multi-slug plugging of the fracture, the later injected gelant slugs pass through the weak areas of the prior matured gel slugs and continue to move behind them instead of pushing the prior matured gel as a whole to the distal portion of the fracture. After the polymer gel one-step plugging of the fracture, chasing water will pass through the edges of the fracture where the gel is not adequately filled or directly through the mature gel in the form of wormholes. In contrast, after multi-slug plugging of the fracture, the mature gel is not easy to be breached by chasing water because of the compaction effect, while the junction between the mature gels of each slug will become an easy area for chasing water to break through. But it is still more difficult to break through than the one-step plugging process. This research is informative for the improvement of polymer gel systems and their successful application in fractured reservoirs for conformance control and water shutoff.

Enhancing temperature resistance of polymer gel fracturing fluids: The role of alcohol

The temperature resistance of polymer gel fracturing fluids is the key to ensure its application in deep oil and gas reservoirs. Currently, the methods to improve the temperature resistance of polymer gel fracturing fluids are mainly based on the additives commonly used in fracturing fluids, but rarely studied on improving the strength of crosslinked systems by strengthening its non-covalent interactions. Herein, we separately introduce ethanol and glycol into the partially hydrolyzed polyacrylamide (HPAM) crosslinked zirconium polymer gels to form the fracturing fluid system with higher temperature-resistant ability. The concentrations of the HPAM and crosslinking agent are all 0.6 wt%. After shearing at 120 °C and 170 s−1 for 1 h, the addition of ethanol and glycol can increase the retention viscosity of the polymer gels from 43 mPa s to 148 mPa s and 204 mPa s, respectively. Microscopic characterization demonstrates that the addition of ethanol and glycol makes the polymer gels more dense “honeycomb” and “dendritic” structures, which may be the main reasons for the temperature resistance enhancement of the system. Additionally, the molecular dynamics simulations show that the supramolecular interaction in the polymer gel system is greatly enhanced by the formation of hydrogen bonds when the alcohol is added at low concentrations. Meanwhile, the zirconium ions play a bridging role in connecting oxygen atoms in the carboxyl group in HPAM and oxygen in the alcohol hydroxyl group. The hydrogen bonds and O-Zr-O bridges can strengthen the non-covalent interactions of the system, inhibiting the destruction of polymer gel structure at high temperatures and enhancing its temperature resistance. However, when the alcohol concentration of the system is too high, the crosslinking strength of the polymer gels is weakened to different degrees due to the competitive effect of the alcohol on the crosslinking agent. Both experimental results and theoretical simulation further deepen the understanding of alcohol to improve the temperature resistance of polymer gels, and can promote the subsequent application of alcohol to polymer gel fracturing fluids for property enhancement.

Laboratory evaluation of high-temperature resistant lysine-based polymer Gel systems for leakage control

In-situ crosslinking gel known for its cost-effectiveness, has been employed for decades to plug high-permeability features in subsurface environments. However, some commonly used crosslinkers are being phased out due to the increasingly rigorous environmental regulations. As a newly discovered environmentally friendly crosslinker, lysine can crosslink the partially hydrolyzed polyacrylamide through transamidation reaction. The present work aimed to study the effect of polymer composition and concentration on the gelation behavior of lysine and high molecular weight acrylamide-based polymers. Several commercial high molecular weight polymers with different contents of 2-Acrylamido-2-methyl-1-propane sulfonic acid (AMPS) including AN-105/125, SAV-55/37/28, and SAV-10 were deployed in this work. High-temperature/pressure-resistant glass tubes were used to study the crosslinking behavior. The plugging efficiency test used a high permeability sandstone core (1600 mD). Besides, the effect of salinity and pH on the crosslinking behavior, gel strength, and long-term thermal stability was also studied. Results showed that increasing the AMPS content could prolong the gelation time, but the polymer and lysine mixture failed to form gels when the AMPS content was excessively high. Additionally, increasing the AMPS content negatively affects the gel strength but positively impacts long-term thermal stability. Polymer gel with a relatively high content of AMPS could be stable in 0.5 % CaCl2 solution at 130 °C for over 200 days. The polymer/lysine gel system can efficiently plug the high permeability matrix, and the plugging efficiency is higher than 99 %. The polymer/lysine gel system is a promising green leakage control system in treating the high conductivity features in geothermal and oil reservoirs.

Electrothermally powered synergistic fluorescence-colour/3D-shape changeable polymer gel systems for rewritable and programmable information display.

Intelligent luminescent materials for rewritable and programmable information display have long been expected to be used to address potential environmental concerns stemming from the extensive use of disposable displays. However, most reported luminescence-colour changeable examples are chemically responsive and not well programmed to sequentially deliver different information within a single system. Additionally, they may suffer from residual chemical accumulation caused by the repeated addition of chemical inks and usually have poor rewritability. Herein, we draw inspiration from the bioelectricity-triggered information display mechanism of chameleon skin to report a robust electrothermally powered polymer gel actuator consisting of one soft conductive graphene/PDMS film and one humidity-responsive fluorescence-colour changeable CD-functionalized polymer (PAHCDs) gel layer. Owing to the good electrocaloric effect of the bottom graphene film and excellent hygroscopicity of the top PAHCDs gel layer, the as-designed actuator could be facilely controlled to exhibit reversible and synergistic 3D-shape/fluorescence-colour changeable behaviours in response to alternating electricity and humidity stimuli. On this basis, robust rewritable information display systems are fabricated, which enable not only on-demand delivery of written information, but also facile rewriting of lots of different information by the synergization of electroheat/humidity-triggered local 3D-deformation and fluorescence-colour changes. This work opens new avenues of research into rewritable information display and potentially inspires the future development of intelligent luminescent materials.

Evaluation of Polymer Gel Electrolytes for Use in MnO2 Symmetric Flexible Electrochemical Supercapacitors.

Flexible electrochemical supercapacitors (FESCs) are emerging as innovative energy storage systems, characterized by their stable performance, long cycle life, and portability/foldability. Crucial components of FESCs, such as electrodes and efficient electrolytes, have become the focus of extensive research. Herein, we examine deep eutectic solvent (DES)-based polymer gel systems for their cost-effective accessibility, simple synthesis, excellent biocompatibility, and exceptional thermal and electrochemical stability. We used a mixture a DES, LiClO4-2-Oxazolidinone as the electroactive species, and a polymer, either polyvinyl alcohol (PVA) or polyacrylamide (PAAM) as a redox additive/plasticizer. This combination facilitates a unique ion-transport process, enhancing the overall electrochemical performance of the polymer gel electrolyte. We manufactured and used LiClO4-2-Oxazolidinone (LO), polyvinyl alcohol-LiClO4-2-Oxazolidinone (PVA-LO), and polyacrylamide-LiClO4-2-Oxazolidinone (PAAM-LO) electrolytes to synthesize an MnO2 symmetric FESC. To evaluate their performance, we analyzed the MnO2 symmetric FESC using various electrolytes with cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The FESC featuring the PVA-LO electrolyte demonstrated superior electrochemical and mechanical performances. This solid-state MnO2 symmetric FESC exhibited a specific capacitance of 121.6 F/g within a potential window of 2.4 V. Due to the excellent ionic conductivity and the wide electrochemical operating voltage range of the PVA-LO electrolyte, a high energy density of 97.3 Wh/kg at 1200 W/kg, and a long-lasting energy storage system (89.7% capacitance retention after 5000 cycles of GCD at 2 A/g) are feasibly achieved. For practical applications, we employed the MnO2 symmetric FESCs with the PVA-LO electrolyte to power a digital watch and a light-emitting diode, further demonstrating their real-world utility.

Effect of nano TiO2 and SiO2 on gelation performance of HPAM/PEI gels for high-temperature reservoir conformance improvement

Nanoparticles have been widely used in polymer gel systems in recent years to improve gelation performance under high-temperature reservoir conditions. However, different types of nanoparticles have different effects on their gelation performance, which has been little researched. In this study, the high-temperature gelation performance, chemical structure, and microstructure of polymer gels prepared from two nanomaterials (i.e., nano-SiO2 and nano-TiO2) were measured. The conventional HPAM/PEI polymer gel system was employed as the control sample. Results showed that the addition of nano-TiO2 could significantly enhance the gel strength of HPAM/PEI gel at 80 °C. The gel strength of the enhanced HPAM/PEI gel with 0.1 wt% nano-TiO2 could reach grade I. The system also had excellent high-temperature stability at 150 °C. The enhanced HPAM/PEI gel with 0.02 wt% nano-TiO2 reached the maximum gel strength at 150 °C with a storage modulus (G′) of 15 Pa, which can meet the need for efficient plugging. However, the nano-SiO2 enhanced HPAM/PEI polymer gel system showed weaker gel strength than that with nano-TiO2 at both 80 and 150 °C with G′ lower than 5 Pa. Microstructures showed that the nano-TiO2 enhanced HPAM/PEI gel had denser three-dimensional (3D) mesh structures, which makes the nano-TiO2 enhanced HPAM/PEI gel more firmly bound to water. The FT-IR results also confirmed that the chemical structure of the nano-TiO2 enhanced HPAM/PEI gel was more thermally stable than nano-SiO2 since there was a large amount of –OH groups on the structure surface. Therefore, nano-TiO2 was more suitable as the reinforcing material for HPAM/PEI gels for high-temperature petroleum reservoir conformance improvement.

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.

Tough PEGgels by In Situ Phase Separation for 4D Printing

AbstractPolymer gels, consisting of cross‐linked polymer network systems swollen by a solvent, show great potential in biomedicine, flexible electronics, and artificial muscles, due to their tissue‐like mechanical properties. Due to the presence of a large amount of solvent, the improvement of the mechanical properties of the polymer gel is a challenge. Moreover, combining high toughness with useful properties, such as 3D printability or shape‐memory, in one polymer gel system is even more challenging. In this study, a simple and efficient method is developed for the fabrication of tough polymer gels by polymerizing 2‐hydroxyethyl methacrylate (HEMA) in a mixture of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). The polymerized elastic networkpresents distinct compatibility with PEG (compatible) and PPG (poorly compatible), resulting in in‐situ phase separation at the microscale. The resulting phase‐separated gel demonstrates high strength (8.0 MPa), favorable fracture strain (430%), and large toughness (17.0 MJ m−3). The separated hard phasewith a high glass transition temperature (75 °C) endows the whole soft polymer gel with the property of shape memory at room temperature. Finally, the fabrication of tunable tough PEGgels is combined with 3D printing as well as with shape memory properties, demonstrating the use of PEGgels for 4D printing.

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%.

Self-filling and plugging performance of a thixotropic polymer gel for lost circulation control in fractured formation

Drilling fluid loss in fractured formations hinders the progress of oil and gas exploration and its development worldwide. Improving the success rate of lost circulation control in fractured formations of oilfields worldwide is crucial for safe, efficient, and economical drilling. The thixotropy of gel solution is an important factor affecting the fracture space filling and plugging performance of thixotropic polymer gel. In this work, a thixotropic polymer gel with shear thinning and static thickening is used as a plugging agent for fractured formations. The self-filling behaviour and plugging performance of the gel in fractures were studied by visual physical simulation. The results showed that the thixotropic polymer gel was less affected by the fracture width when filling in the fracture, which could realize the uniform filling of the 12 mm wide fracture space. In addition, the thixotropic polymer gellant could be pumped in at high shear rates and retained in the loss space at low shear rates. Meanwhile, the plugging performance of the thixotropic gel on different scales of fractures was studied. Thixotropic polymer gel system could reside in different fracture types (uniform fracture, wedge-shaped fracture) and different fracture sizes. The breakthrough pressure of the thixotropic polymer gel in the wedge-shaped fracture was higher than that in the uniform fracture for identical outlet sizes. The thixotropic polymer gel had a pressure bearing capacity of 6.6 MPa in a wedge-shaped fracture with 5 mm width. The pressure bearing capacity of the gel to the wedge-shaped fracture with a width of 3 mm at the outlet reached 7.3 MPa, showed excellent pressure bearing capacity. The study on the self-filling behaviour and plugging performance of thixotropic polymer gel could provide theoretical and technical reference for efficient plugging in the drilling process of fractured formations.

Cross-Linking of Oxidized Hydroxypropyl Cellulose in Paper: Influence of Molecular Weight and Polymer Distribution on Paper Wet Strength Development.

With the overarching aim for the development of sustainable, nontoxic wet strength agents for paper, a novel polymer gel system based on oxidized hydroxypropyl cellulose (keto-HPC) cross-linked with polyamines was investigated in detail to gain a deeper insight into the wet strength mechanism. When applied to paper, this wet strength system significantly increases the relative wet strength by using only low amounts of polymer, and it is therefore comparable with established wet strength agents based on fossil resources, such as polyamidoamine epichlorohydrin resins. With the help of ultrasonic treatment, keto-HPC was degraded with respect to its molecular weight and further cross-linked in paper using polymeric amine-reactive counterparts. The resulting polymer-cross-linked paper mechanical properties were analyzed with respect to the dry and wet tensile strength, respectively. In addition, we analyzed the polymer distribution using fluorescence confocal laser scanning microscopy (CLSM). If high-molecular-weight samples are being used for cross-linking, we do find accumulation of the polymer mainly on the surface of the fibers and at fiber crossing points, accompanied with enhancing strong effects on paper's wet tensile strength. In contrast, if low-molecular-weight (i.e., degraded) keto-HPC is being applied, the macromolecules are capable of entering the inner porous structure of the paper fibers, and almost no accumulation at the fiber crossing points is observed, which also results in a lowered wet paper tensile strength, respectively. This insight into wet strength mechanisms of the keto-HPC/polyamine system can thus lead to new opportunities for the development of alternative biobased wet strength agents where molecular weight dependence of the wet tensile properties allows for a fine tuning of mechanical properties in the wet state.

Recent advances in enhanced polymer gels for profile control and water shutoff: A review.

Polymer gels have been effectively employed as a water management material for profile control and water shutoff treatments in low-middle temperature and low-middle salinity reservoirs. However, most polymer gel systems have limitations under high temperature and salinity reservoir conditions, such as short gelation time, poor strength, and long-term instability. Therefore, several researchers have developed enhanced polymer gels to satisfy the water control requirements in high temperature and salinity reservoirs. This work reviews the five main types of enhanced polymer gels that have been developed so far: nano silica-enhanced gel systems, cellulose-enhanced gel systems, graphite-enhanced gel systems, oily sludge-enhanced gel systems, and foam-enhanced polymer gel systems. Further, this article investigates the fundamental properties, strengthening and crosslinking mechanisms, reservoir application conditions, and field applications of several enhanced polymer systems. In this paper, it is found that the addition of strengthening materials can increase the bound water content in the gel network and significantly improve the temperature and salt resistance of polymer gel, so as to cope with the application of profile control and water plugging in high temperature and high salt reservoirs. Moreover, it also offers references and future research directions for enhanced polymer gel systems.

Lysine Crosslinked Polyacrylamide─A Novel Green Polymer Gel for Preferential Flow Control.

Acrylamide-based polymer gels have been applied to control the preferential flow in the subsurface for decades. However, some commonly used crosslinkers, such as Cr (III) and phenol-formaldehyde, are highly toxic and are being phased out because of stringent environmental regulations. This work uses l-lysine as the green crosslinker to produce acrylamide-based polymer gels. This article systematically studied the effect of lysine and polymer concentration, salinity, pH, and temperature on gelation behavior and thermal stability. Besides, the gelation mechanism and crosslinking density were elucidated in this work. A high-permeability sandstone core was used to test the plugging efficiency of this novel green gel system. This polyacrylamide/lysine system has a controllable gelation time. It can form gels at temperatures higher than 80 °C, with the gelation time from hours to days, and the elastic modulus of the gel can reach over 400 Pa. In addition, the crosslinked gels have been stable at 80 to 130 °C for over 200 days. This novel gel system could decrease rock permeability by over 1000 times. Besides, the Frrw is two times higher than the Frro, confirming that the current gel system can reduce the permeability to water more than that to oil. As a green gel system, this novel polymer gel system could replace the current toxic gel systems for the preferential fluid control for water management projects in oil and gas reservoirs, enhanced geothermal systems, and carbon capture and sequestration projects.

Gelation of an Organically Crosslinked PHPA Polymer Gel System: An Experimental Study

Excessive water production in the oil field is the major difficulty in production for the petroleum industry. Remedial techniques need to be applied to control this excess water production considering the health, safety, and environmental issues and improve the reservoir's economic and productive life. In this study polymer gel system comprising the polymer partially hydrolyzed polyacrylamide (PHPA) and organic cross-linkers (Hydroquinone and Hexamethylene tetramine) were prepared as a water shut-off system to control the excessive production of water in the oil field. The effect of various parameters such as temperature, pH, cross-linker concentration, degree of hydrolysis, and divalent cations on gelation time was investigated using the bottle testing method. The importance of retarders at high temperatures was also evaluated. The gelation temperature was varied from 90 °C to 120 °C to study the effect of different parameters on the gelation time and gel behavior. This study suggests that Partially Hydrolyzed Polyacrylamide (PHPA) with organic cross-linkers can be an effective polymer gel system for water shut-off operations, and with the addition of retarders at high temperature to control gelation time, the performance of the gel can be improved.

Gelation Behavior of Polyacrylamide-Polyethyleneimine: Effects of Diethylenetriamine and Glycerol Addition

Polymer gel systems find applications in diverse areas, ranging from contact lenses to agriculture and oil production. In general, polyacrylamide (PAM) gels are produced by reaction with metallic (low temperatures) and organic (high temperatures) crosslinking agents. In this paper, given crescent environmental concerns, polyethyleneimine (PEI), an organic reactant, was chosen as the crosslinker of PAM, at 65 ºC. The effects of using a solution of water/glycerol as the solvent for preparing the gels and the addition of diethylenetriamine (DETA), a n-alkylamine, on the gelation kinetics and gel stability were evaluated. The data presented in this paper indicates that the solvent mixture provided a more controlled gelling behavior by means of delaying the gelation time. Also, diethylenetriamine acted both as an efficient anti-syneresis agent, improving gel stability, and by delaying the progress of gel’s strength.

Feasibility Study of Recrosslinkable Preformed Particle Gels for Natural Gas Injection Profile Control

SummaryRecrosslinkable preformed particle gel (RPPG), a preformed particle gel (PPG) of which particles can bond together to form a strong bulk gel system after being placed inside the target formation, has been successfully applied to control conformance problems for waterflooding projects. However, no research has been conducted about whether RPPG is feasible in improving gasflooding performance in mature reservoirs. The study presents a systematic evaluation of acrylamide (AM) and 2-acrylamide-2-methylpropane sulfonate acid (AMPS)-based RPPG including phase stability under different gel-gas kinetics and plugging performance to natural gas and water. Different experimental apparatuses were designed to quantify and visualize the RPPG phase stability under static and dynamic gel-gas interactions. The RPPG phase stability was evaluated under a different range of injection pressure, gas exposure time, and swelling ratio (SR). Also, the RPPG stability was compared to the in-situ gel system hydrolyzed polyacrylamide crosslinked with chromium acetate [HPAM/Cr(III)], which has been applied in oil fields to control gas injection conformance. The RPPG plugging efficiency was evaluated using open fractured cores with different apertures. The results showed that the RPPG was stable under both static and dynamic gel-natural gas interactions and was stable when being exposed to an acidic environment with an insignificant total percentage weight loss (<3%). Additionally, the strength of the RPPG was further improved with the longevity of the gas exposure. Furthermore, different from the in-situ gel system HPAM/Cr(III), which exhibited a high degree of dehydration under natural gas and exhibited substantial syneresis under acidic conditions, the microstructure of the RPPG remained stable after the dynamic gas exposure. The results of the coreflooding experiments demonstrated that the RPPG had excellent plugging efficiency, which was closely related to the SR and the fracture aperture. This is the first study where a polymer gel system has been systematically assessed through varied testing methodologies using natural gas as opposed to other studies where nitrogen (N2) was used to simulate natural gas behavior. The robustness of the RPPG system makes it a viable candidate for improving the gasflooding processes in mature reservoirs dominated by conformance problems such as void space conduits (VSCs), fractures, and high-permeability channels.

Experimental study on compatibility of reservoir and polymer gel profile control agent

The coupling relationship between polymer gel system and reservoir pores is an important basis for scientific formulation of tertiary oil recovery programs. The polymer gel profile control agent can significantly modify the fluid migration path inside the reservoir. In this study, artificial cores were used to carry out indoor water flooding experiments after polymer gel injection that considering formation permeability, polymer concentration and polymer injection rates. Based on the accurate records of the breakthrough pressure and injection volume during water flooding, as well as a large number of observations of the microscopic morphology of the cores after the polymer gel profile control and displacement, a set of criteria for determining reservoir-matched polymer gel profile control agents is proposed. The experimental results show that a complex spatial network structure is formed after the gelation of the polymer gel system. As the polymer concentration increases, the network structure of the gel system becomes denser. At the same time, the unit network structure is becoming smaller, and the order of the grid chain structure becomes clearer. Under the condition of low polymer concentrations, the backbone structures of the gel are obvious, but there are a lot of fine pores. When the polymer concentration is greater than 1,500 mg/L and the injection rate is less than 0.15 ml/min, the water flooding breakthrough pressure is greater than 0.2 MPa, the plugging rate is greater than 95%, and a good plugging effect is obtained.

Polyacrylamide Polymer Gel Systems for Conformance Control Technology: A Review

Low oil extraction and early high water production are caused in part by reservoir heterogeneity. Huge quantities of water production are prevalent issues that happen in older reservoirs. Polyacrylamide polymer gel systems have been frequently employed as plugging agents in heterogeneous reservoirs to regulate water output and increase sweep efficiency. Polyacrylamide polymer gel systems are classified into three classes depending on their composition and application conditions, which are in-situ monomer gel, in-situ polymer gel, and preformed particle gel (PPG). This paper gives a comprehensive review of PPG’s status, preparation, and mechanisms. Many sorts of PPGs are categorized, for example, millimeter-sized preformed particle gels, microgels, pH-sensitive cross-linked polymers, swelling polymer grains, and Bright Water®. In addition to this, the most important factors to consider while assessing gel performance, such as swelling capacity, PPG injectivity, and plugging efficiency, are studied carefully. Not only are the design considerations and field application of PPG mentioned, but also the advantages of PPG are demonstrated. Gels have been used in around 10,000 wells worldwide to reduce the fractures permeability or super-high permeability channels during water and polymer floods.

A selective water control and gas augmentation method based on APR gel

Water production will seriously affect the economics of gas well in the development of oil field. However, the conventional water shutoff agent is easy to block the gas flow channel at the same time of plugging the water. In this paper, a temperature and salt resistant polymer gel system composed of acrylamide/acryloyl morpholine/vinylpyrrolidone terpolymer (APR) and polyethyleneimine/modified alumina nanoparticle cross-linker was developed. At the same time, a selective water control and gas augmentation method based on APR gel was established. The effect of gel composition on its performance was mainly studied, and the water & gas shutoff performance in harsh environment was also researched by sandpack flow experiment. The gelation time could be controlled within 2–14 h by adjusting the concentration of the polymer, cross-linker, and deoxidant. In addition, the dehydration rate of the gel was only 2.6% after 180 days heat aging at 107 °C and 230,000 mg/L mineralization. The scanning electron microscope (SEM) showed that the uniform distribution of the network structure resulted in the gel with excellent stability in harsh environments. Sand filling experiments indicated that the plugging rate of gel for sand filling models with different permeability was all above 90% in harsh environment (107 ℃, 230000 mg/L salinity). Besides, laboratory experiments have illustrated that the injection pattern of the gel has a significant influence on its water & gas shutoff performance. Injecting 0.5PV gel solution first, then injecting 6PV N2, the shutoff performance of gel for water was nine times as good as that of gas. The research provides technical guidance for the water shutoff of high-temperature and high-salt gas reservoirs.