Potential Advances in the Design of Sealants for Geologic Conformance Control toward CO₂ Storage Security

Abstract

The global warming crisis, traceable to the rise in greenhouse gas emissions, has called for more proactive measures to curb the emission levels. To this effect, several technologies have been suggested. Out of the lot, carbon capture, utilization, and storage have been identified as one of the most feasible and pragmatic methods. This is partly because the concept, technical resources, and facilities are transferable from CO₂ injection and enhanced oil recovery applications. For this reason, studies centered around CO₂ conformance control for subsurface storage have been conducted. Also, reviews on the classification and description of chemical materials utilized for the conformance control have been published. With the limitations of these materials in mind, this review extends the types of sealants that can be applied for CO₂ entrapment in subsurface geologic formations. The group of gelants that generally fall under multicomponent polymer systems and viscoelastic fluids was evaluated. The review describes their properties, behavior, response to CO₂, and other unique features that make them suitable to be considered for reservoir conformance control purposes. Based on the review, recommendations for future studies on these novel materials were given.

1.0. Introduction

Several techniques have been suggested and developed to mitigate the release of carbon dioxide (CO₂). However, based on nearly 100 years’ experience of injecting, storing, and recycling both fluids and natural gas in the oil and gas industry, the storage of carbon dioxide (CO₂) in deep subsurface reservoirs is technically the most feasible strategy for reducing emissions of CO₂. This mitigation option is most effective when used in combination with other options like enhanced oil recovery and energy efficiency. It is widely believed that it could achieve a major reduction in atmospheric greenhouse gas emissions. Hence, the use of carbon capture, utilization, and storage (CCUS) technologies has been endorsed by many environmental agencies and stakeholders. Thus, CO₂ geo-storage systems represent a new paradigm for managing the carbon footprint. − As for the geologic storage site, brown oil and gas reservoirs will be more favorable because, besides existing infrastructures, injection of CO₂ for combined enhanced recovery and underground storage at the site will be more acceptable to both operators and policymakers. However, due to the heterogeneity of these reservoirs, the possible presence of conducting fractures, and the potential failure of sealing caprocks, the gas channelling of CO₂ may become a more serious problem. Therefore, finding an effective method for gas channelling control will be a critical issue for CO₂ geo-storage processes.

Traditional conformance control in subsurface formations usually involves the injection of organic and inorganic non-Newtonian materials into these formations. The essential feature is that these materials can reattain their viscosity and elasticity within the porous media, expand, and thicken up therein. This way, they fill up the thief zones within reservoirs like highly permeable regions, fractures, and vugs. In subsurface engineering, this technique is often used to control the directional displacement and migration of reservoir fluids, hence, it can also be used to permanently contain gaseous fluids such as CO_2. CO₂ conformance control in subsurface reservoirs using sealants has been the central theme of much research in literature. Some studies have focused on the development of novel and smart gels for conformance control in reservoirs and their attendant effect on mobility control. − Others have been geared more toward conformance control in storage sites. To this effect, several reviews on sealants for CO₂ subsurface storage exist in the literature. ,− Collectively, these research references have focused on using Cementitious materials, organic-based gels like cross-linked polymers and resins, and inorganic polymers. Cement is largely characterized by degradation in the presence of CO₂ and/or acidic conditions, which can be aggravated by the prevailing operating conditions in the wellbore. Figure demonstrates possible ways by which CO₂ can undergo seepage within the well completion due to the failure of the cement. While the inorganic gels have better chemical and thermal stability, their usefulness for deep reservoir profiling is limited. On the other hand, the adhesive and plugging properties of organic gels are debatable, even though they have better injectivity. As these classes of chemicals have significant limitations, this review aims to reduce these limitations by extending the scope of the search for suitable sealing materials used for plugging in the subsurface. Thus, the review takes a critical look at the potential of other sealant materials that can have better adaptability to CO₂ coupled with other conditions in the subsurface environment, thereby having a significant effect on sealing performance. Hence, this review systematically evaluates classes of chemicals under multicomponent polymer systems and viscoelastic fluids. Finally, suggestions are given on how to improve the design, development, and selection criteria of these novel materials.

1.

Possible ways by which CO₂ can migrate and be channelled within a well encasement: from a highly permeable or fractured formation (a) into a poorly consolidated and shrunk cement sheath (c) through gaps (b). Also, CO₂ can dissipate within the cracks in the cement and flow into the spacing (d) at the back of the casing (e). Here, CO₂ can easily migrate to the surface and immediate environment through seepage conduits (b) and (d). The arrows signify the direction of migration of mobile CO₂.

2.0. Advances in Composite Materials Application

2.1. Interpenetrating Polymer Network Gels

An interpenetrating polymer network (IPN) is a polymer composite comprising two or more species of polymeric chains that are either orderly or disorderly interlaced or simply entangled. The polymer networks are not covalently bonded to each other. however, they are so closely interknitted that the chemical monobonds need to break before they can be separated or pulled apart. Thus, the inter-relationship within these networks is different from that of copolymers wherein the latter is when different species of monomers polymerize into a multicomponent polymer chain. Figure depicts how fluorescent polymer gel, a novel microsphere, was synthesized by introducing the monomer fluorescein as a secondary network into a primary network composed of cross-linked AM and AMPS. Spectroscopic methods like Raman microscopy and infrared spectra delineate between a covalently formed multiblock multifunctional copolymer and an interpenetrating network. − The development of gels based on interpenetrating polymer networks in reservoir conformance control has received much attention lately, with applications in improved oil recovery, and CO₂ leakage remediation.

2.

Development of a multicomponent multinetwork polymer gel where acrylamide monomer, 2-acrylamido-2-methylpropanesulfonic acid, and fluorescein monomer are cross-linked using N,N′-methylene-bisacrylamide. Reprinted from Shagymgereyeva et al. “Performance Evaluation of Fluorescent Polymer Gel Microspheres as a Reservoir Conformance Control Agent”. Copyright Gels 2025, 11, 85. (http://creativecommons.org/licenses/by/4.0/).

The IPN concept can be used to develop tough, tolerant, and highly adaptable gels for subsurface conditions. The different polymer strands often compensate for each other’s weaknesses. For instance, a rigid cross-linked polyelectrolyte was combined with an elastic polymer network to develop a resin system. , The design integrated the high tensile stress tolerance of the former with the elasticity of the latter to come with a new product with high strength and less susceptibility to crack. The main ideology behind IPNs for product design, just like we have it in other composite materials, is to embed the desired qualities of individual melts into the resultant polymer system while complementing their limitations. As such, multiple interpenetrating networks can be used to develop smart CO₂-responsive polymers with high tolerance for harsh temperature, brine salinity, and hardness conditions typical of targeted CO₂ subsurface storage sites. A Novel CO₂-responsive preformed gel with an interpenetrating network was synthesized by combining AFAPE-20 and DMAEMA, and it was proposed for the mitigation of CO₂ breakthrough in fractured tight reservoirs. Because the polymeric cross-linked network contained protonable functional groups, the gel swelled with enhanced viscosity and particle strength after coming in contact with CO₂. Although this is reversible. The formulation, IPN-PAASP, exhibited good plugging attributes when injected into a fractured core, with a rise in injection pressure from 5.0 kPa to 0.342 MPa. The studies have revealed that when protonation takes place via CO₂ interaction, the hydrophilicity of the compound increases thereby allowing more water molecules to invade the nanospaces of the network and be trapped thereof. Hence, the swelling of the gels. Therefore, the rheological property of IPN-PAASP suspension, and particle strength, favored plugging. Rheological analysis showed that IPN-PAASP suspension had pseudoplastic and dilatant fluid characteristics, enhancing its plugging capacity. With the success of this novel IPN material, the study can be extended by looking at the long-term stability of IPN-PAASP at subsurface operating conditions coupled with field-scale validation.

Studies have revealed that the mixing of PAM-based polymeric chains with that of natural polymers like alginate can produce IPN hydrogels with tunable rheological properties. , Also, the IPN method can be used to improve the physiochemical properties of conventional preformed particle gels. Here, desired attributes like reversed self-healing of broken cross-linked covalent bonds in the gel network can be induced, thereby developing a more robust and mechanically stable product. − The self-healing function is one of the criteria that characterize a material as being smart. The importance of this attribute cannot be overemphasized, especially for improvement in preformed particle gel technology. The associative tendencies in IPNs which inadvertently promotes self-healing and reinforcement behaviors, even in harsh reservoir conditions of high brine hardness and high temperature, were noticed in Stimuli-responsive poly­(acrylamide-co-vinyl acetate)/alginate-based hydrogel particle. Figures a and b show how the gels visibly heal when cracked fragments are brought together. Figure c further explains how this takes place at the molecular level within the matrix of the polymer network. The particle, having a stable three-dimensional network structure, can swell twice its original volume. However, the elastic modulus is selectively dependent on the brine type and concentration. As expected, the pH controlled the rate of protonation of the cross-linker within the network, and this dictates the self-association properties as well as the gelation kinetics. The protonation of the amide groups aids in forming strong intramolecular bonds, while the interaction of the divalent cations with the oligosaccharide chain aided in the reinforcement process when it created a hard ion-core–shell gel structure. Thus, contrary to previous observations on preformed particle gels, AIPNG systems’ bulk, and elastic modulus increased with temperature and swelling , thereby contributing to the mechanical strength of the gel. Field trials were also carried out in the Zhidan area to test the AIPNG product. Thus, Further studies to characterize the Alg-IPNG gel’s healing properties discovered that it demonstrated self-healing properties and has enhanced thermal stability (180 days) at temperatures up to 110 °C. Hence, this infers that it can be used in remediating fracture-like conduit problems in high-temperature reservoirs. The Chromium ion embedded Alg-IPNG complex, a porous network structure, demonstrated absorptive properties which contributed to the swellability. It also has a good elastic modulus. However, temperature and Ca²⁺ concentration tend to affect the self-healing time and mechanical strength. To further address the reversed protonation that occurs at high temperatures leading to the deswelling of cross-linked gels, Du et al. prepared dispersed particle gels (DPG) made out of a double network of polyacrylamide and sodium alginate. The gel was modified by introducing potassium methylsilanetriolate (PMS) upon shearing it in water to make the gel particles. Aging at 100 °C for 1 day and additional thermogravimetric analysis confirmed the thermal tolerance of the suspension. The gel demonstrated a high mechanical strength of 0.259 MPa and a toughness of 1.17 MJm^–2. The novel particle gel also exhibited channel-plugging capabilities in ultrahigh permeability sandpacks when they achieved a plugging efficiency of 95.3% compared to that of regular particle gel with 82.8%. Thus, aside from improving the swelling performance at high temperatures, the PAM-SA-PMS gel also eliminated the challenge of poor swellability in a high-saline environment.

3.

Self-healing mechanism of Alg-IPNG particle gels. Cracked elastomers (a) when brought together rebind perfectly (b). The material healing is depicted at the molecular level (c). Pictures (a) and (b), and figure (c) courtesy of Pu et al. “Systematic Evaluation of A Novel Self-Healing Poly­(acrylamide-co-vinyl acetate)/Alginate Polymer Gel for Fluid Flow Control in High Temperature and High Salinity Reservoirs.” Copyright Polymers 2021, 13, 3616. (http://creativecommons.org/licenses/by/4.0/).

Aside from the normal interpenetrating polymer networks, supramolecular networks can also be used to design composite polymeric systems. They are composed of a regular polymer, a cross-linker, a gel factor, and a polarity regulator. This design is similar to the host–guest concept in polymeric materials and can be used to develop very strong and stable gels. Two or more networks can be formed within the polymer architectural matrix using both covalent cross-linking and ionic-controlled hydrophobic–hydrophilic interactions. Based on this design, Ma and Co developed a novel supramolecular-composite gel intended for plugging fractured formations. Their investigations revealed that the novel material has good plugging tendencies. As depicted in Figure , the viscoelastic performance of the composite systems is significantly enhanced compared to single-component polymer networks. A unique feature of this material is the ability to temporarily disassemble the nonchemical bonds to relieve the internal stress under strain. This is important to product stability and resistance to degradation in situ. A major setback for IPNs is the reduction in the injectivity of reinforced gels because of the higher elasticity modulus that can be generated in situ.

4.

Viscoelastic performance of the supramolecular-polymer network composite as compared to single network polymer and supramolecular gels. Adapted from Ma et al. “Development and Performance Evaluation of a New Conformance Control Agent.” Gel Copyright Gels 2024, 10, 618. (https://creativecommons.org/licenses/by/4.0/).

2.2. Nanocomposite-Enhanced Gels

Nanotechnology is a perspective that should be considered for application in the CO₂ leakage control processes. This is because it has a high potential to improve plugging performance in formations. Nanoparticle reinforcement is a common thing in the enhancement of the mechanical properties of gels. , Reinforced systems are described as systems containing polymers, cross-linkers, and nanomaterials. The method entails embedding nanoparticles into gel systems, thereby enhancing their mechanical strength and other targeted properties. Nanoparticles can act as cross-linkers so that the gel strength improves as the nanoparticle concentration increases. Also, the unsaturated functional groups on polymer chains such as the carbonyl group or branched covalent double bonds on alkyls can interact with nanoparticles such as silica. Such connections can improve the texture and structure of the fabric of the gel network and prevent degradation. Besides mechanical stability, other physicochemical properties that can be infused from the combination of polymer and nanoparticles are thermal stability, chemical resistance, upgrade in rheological characteristics, and of course, stimuli-responsiveness to certain external factors. − In practice, for wellbore reconditioning, the nanoparticles can be mixed with the Portland cement or geopolymer cement and be displaced into the hole. For deep reservoir profiling, the nanoparticles can be combined chemically or nonchemically with diversion agents like polymer gels or foam. Yet again nanoparticles can just be deployed as a suspension in brine, percolating within pore spaces and forming hydraulic barriers thereof. The specific technique selected depends on the type of application and the location of deployment. The rheological properties of a silica nanoparticle-enhanced PVOH gel were noticed to depend on the subsurface formation conditions such as temperature and the presence of salts. For either parameter investigated, calcium and sulfate salts have the most prominent influence on gel viscosity, compared to sodium salts; for instance, the sulfate ions caused an increase in the viscosity. Also, the gel starts to swell at a temperature of 55 °C. Nanoclays are another interesting additive that can improve the properties and performance of polymer composites. In a study, Nanoclay particles were used to physically cross-link AM and AMPS in the polymer network, thereby leading to an improvement in thermal stability compared to regular PPGs. Also, by optimizing the compositional aggregates, the clay-based nanoparticles improved the rheology, mechanical strength, and salt tolerance of the reinforced PPG. Flow test in a brine-saturated sandpack revealed that the NC-PPG attained a plugging rate of 94.3% with a residual resistance factor of 17.6. However, NC-PPG exhibits high sensitivity to alkaline pH. Nevertheless, the presence of nanoclay in the polymer composite enhanced the water absorbency, explaining the high swelling rate.

Among the benefits of nanoparticles, it is interesting to know that they can boost cross-linking across the different monomer species in a composite system as seen in Figure . This is particularly important because they can serve as a sustainable option to substitute for conventional synthetic cross-linking agents in polymerization reactions. Lashari and colleagues were able to introduce silica nanoparticles into the R-80-HMTA-PADC polymeric system. This improved the cross-linking across the network which invariably boosted the structural integrity and mechanical strength of the material. Silica nanoparticles also increased the cross-link density of a hydrogel which resulted in a significant increase in the gel strength. A study investigated the effects of nanoparticles on the properties and behavior of a nano-SiO₂-strengthened polymer gel for potential applications in oilfield conformance control. The nanoparticles not only contribute to the cross-linking between hydrolyzed polyacrylamide and the water-soluble resin, but they also controlled and moderated the entanglement and aggregation within the network through absorption via attractive forces such as hydrogen bonding and Van Der Waals’. Furthermore, the nanoparticles imparted hydrophilicity unto the resultant gel system which aided in its stability and strength. This was evident when the gel with nanoparticles had a measure of gel strength four times higher than the gel without nanoparticles. The nanoparticles improved the viscoelasticity of the gel, which is nonlinear in behavior, translating to good ductility and toughness. The authors argued that based on these features, the nanoparticle-strengthened gel would have a good plugging capacity for subsurface formations. Silica nanoparticles have been combined with acrylamide, copolymers, synthetic cross-linkers, and resin ingredients to form a three-dimensional network structure with a very rigid skeleton. The resultant feature was a good temperature and salt tolerance, making them suitable candidates for high-temperature high-salinity reservoirs. The final product was hard, tough, and highly expandable particle gels, and it is envisaged that it might become challenging to process on-site before injection. However, the authors suggested innovative ways by which the gels can be prepared and transported. This is by granulation, followed by an optimized physical film coating treatment approach.

5.

Silica nanoparticles improve the coupling of AM & AMPS in the presence of cross-linkers. Adapted from Li et al. “Synthesis and Performance Evaluation of a Novel Nanoparticle Coupling Expanded Granule Plugging Agent.” Copyright Gels 2023, 9, 479. (https://creativecommons.org/licenses/by/4.0/).

Many studies have revealed that Nanoparticle-embedded gels will have improved gel strength, and long-term mechanical and thermal stability, and are less susceptible to degradation. However, the presence of nanoparticles in the gel network can alter significantly the gelation kinetics. This is a strong function of the constituent of the polymer system. In a study involving HPAM, AM, the water-soluble phenolic resin, and nanosilica particles as stabilizers, the gelation time of AM-AMPS-based polymeric gel was noticed to be longer than that of the ordinary HPAM-based under the same dosage of polymer and cross-linker conditions. Although all the gels exhibited good thermal stability with minimal syneresis after aging for 30 days, the HPAM gels took less than 20 h to form at 65 °C. The implication is that this gel design might not suffice for displacement and deployment for locations far from the wellbore.

CO₂-responsive nanoembedded preformed particle gels for CO₂ conformance control can also be prepared using different synthesis methods. Recently, vinyl silica nanoparticles (VSNPs) were introduced into a cross-linked network which resulted in a 3200% increment in the swelling ratio in an acidic CO₂ environment, as compared to 750% increment in the ordinary aqueous environment. This dramatic increase in swellability was revealed by Differential Scanning Calorimetry to be due to the nanoparticles improving the entrapment of water molecules within the gel network. Although the pore sizes of CO₂-responsive preformed particle gel (CR-PPG) with VSNPs are smaller than those without the nanoparticles. Nevertheless, the Gel was stable up to a temperature of 100 °C and salinity of 10,000 ppm in an acidic environment. While these temperature and salinity conditions are still relatively mild, the CR-PPGs attained a plugging efficiency of 99.92% with a breakthrough pressure of 1.19 MPa in a fractured core. The swelling behavior within the cross-linked network is a result of the repulsion between protonated ions created by the reaction of CO₂ and tertiary amine groups in an aqueous environment leading to the production of ammonium bicarbonate ions.

A couple of studies have looked into nanocellulose particles intercalated within PAM-based polymer networks using a standard free-radical polymerization synthesis route. In particular, the effect of the natural nanomaterial on the mechanical properties of particle gels with various contents of acrylamide was investigated. Here, the overall rheological properties and mechanical strength were boosted several times over. The study also conducted experiments and numerical simulations to observe NPG migration in fractures under varying fracture apertures, NPG diameters, and operating parameters like fluid velocity, NPG concentration, and NPG strength. Five transport patterns in fractures were identified based on fracture characteristics, and the placement of NPG significantly plugged the fractured cores. The NPG also exhibited higher residual flow and washout resistance than PG in fracture models. NPG was able to induce a higher pressure drop in the fracture compared to PG and HPAM. The enhanced performance of nanocellulose-regulated particle gels is traceable to the effects of debonding and sliding within the gel matrix between the acrylamide network and the nanocellulose segments. , However, the established numerical model may be limited because of the irregularities in breakthrough pressure. A way by which the study could be improved is by considering the roughness of fracture surfaces, which could impact the transport behavior and transport patterns of NPG and afterward optimizing these properties for improved conformance control. In all, studies on nanoparticles have not been able to correlate the swellability or positive responsiveness, in terms of rheology, to the presence of CO₂ in situ. In fact, there are limited studies on the direct use of nanoparticle-enhanced gels for CO₂ conformance control.

An advanced nanotechnology-based plugging agent was developed recently. The TS-Nano 20 sealant is a low-viscosity sealant engineered to seal very thin microcracks in wellbores and was developed for CO₂ sequestration. The sealant has superior flowability, low contact angle, and excellent bonding strength for both rock–rock and casing-rock surfaces. It is also very ductile, and thermally stable. Figure shows the exceeding bond strength compared to microfine cement. Moreover, the sealant demonstrated migration abilities into tightly fractured formations under reasonable pressure gradients. From the performance tests conducted and field observations, the sealant was effective in resisting fatigue which could lead to debonding than conventional microfine cement and other sealants. It reduced flow rates by 50–80% immediately after injection, with a slight decrease in sealing capacity after about 1 week.

6.

Bond strength of the novel sealant TS-Nano 20 in 30 μm crack between cement and shale rock surface compared to that of microfine cement fillings. Reprinted from Murcia et al. “Nano Sealant for CO2 Seal Integrity and Overcoring at Mont Terri.” Copyright 15th International Conference on Greenhouse Gas Control Technologies, Abu Dhabi, UAE, March 15–18, 2021.

Another new smart and innovative concept in the development of materials for CO₂ injection integrity and leakage remediation at the wellbores is the deployment of coated nanosealants that can attain deep infiltration into the formation and be programmed to be released based on specific subsurface triggering conditions. Of such is cement-based porous nanoparticles (CPNPs), a sealant material that can be preprogrammed with a range of ingredients that best fit various complicated well/reservoir environments under a variety of temperatures, pressures, and chemical conditions was developed. The CPNPs loaded with sealants were designed to seal cracks in wellbores, cement sheaths, and rock formations. These nanoparticles can flow into small cracks, release sealants, seal various materials, and bond to cement under extreme conditions. The technological concept is depicted in Figure . Unlike existing remediation methods, the technology aims to provide a programmable solution for CO₂ leakage prevention. Future research could look into other types of nanoparticles aside from SiO₂-based. Also, nanosilica has been speculated to be able to improve the compactness and compressive strength of geopolymers at high-pressure and high-temperature conditions. Although nanocomposite gels perform better in harsh reservoir conditions, they are an expensive technology.

7.

Schematics of the CPNP sealant technology. The epoxy resin is coated with Cementous material, and it can perform remedial jobs at the wellbore cracks and in the formation fractures.

3.0. Prospects of Viscoelastic Materials for Formation Sealing Integrity

3.1. Wormlike Micelles

Viscoelastic fluids (VEF) are melts that exhibit a response that resembles that of an elastic solid under some circumstances. This behavior is traceable to the formation of giant reversible micellar aggregates within the molecular framework which makes them act like polymeric materials. Such unique rheological attributes have found usefulness in several facets of industry such as in cosmetics, Laundry, and oil production. − Lately, VEF-based CO₂-triggered smart fluids are gaining traction because of the switchable viscous and elasticity changes they undergo when they come in contact with CO₂. Thus, this feature extends their functionality and potential application to CO₂ mitigation and control. Long-chain cationic surfactants, anionic and cationic Gemini surfactants, and amphoteric surfactants tend to form wormlike micelles (WLMs) in response to high salinity inorganic salts typical of subsurface environments. According to Wu et al., smart WLMs can respond to both pH and CO₂ depending on the functional groups present, wherein electrostatic interactions mainly govern the mechanism of transformation. Based on this, surfactant-derived CO₂-induced smart viscoelastic fluids have been synthesized and tested.

The Gemini surfactant-based viscoelastic fluids are one of the prominent classes of Surfactant-derived wormlike micelles. Smart CO₂-responsive 1c pseudo” Gemini wormlike micelles were formed by reacting erucic acid 3-(N,N-dimethylamino) propylamide (EADP) with maleic acid (MA). Here, pseudo-Gemini in the sense that after the protonation of the amine group on EADP, they interacted with the twin carboxylate group of the maleic acid, wherein the latter served as a spacer. Thus, different morphological transformations of microstructures from spherical micelle to wormlike micelles were observed in response to CO₂ stimuli as described diagrammatically in Figure . It could be said that the noncovalent interactions like electrostatic attraction and repulsion play a crucial role in self-assembly behaviors, wherein the enthalpies of reactions between EADP and CO₂ indicate a hydrophilic transition, and the viscosities of the solutions changed in response to these reactions. Apart from CO₂ promoting the protonation of functional groups such as amine, they can also operate like catalysts in the formulation of Gemini viscoelastic materials. A study revealed how two sodium dodecyl sulfate molecules were bridged to form a pseudogemini surfactant due to noncovalent attraction when diethylenetriamine (DETA) was protonated by the mere introduction of CO₂ into the solution. While the reaction is reversible upon removal of CO₂, the resultant complex behaves like a high-viscosity fluid. Also, the fluid plasticity has a critical concentration beyond which the viscosity increases exponentially. The micellar conformation was theoretically confirmed by a packing parameter of 0.46 for the CO2-SDS-DETA Gemini surfactant. Cryo-TEM also shows overlapping ‘worms’ hundreds of nanometers in length that are closely packed and entangled, forming a continuous 3-D network. The bridging process of SDS, as induced by the protonation of DETA, increased the size of the headgroup and length of the hydrophobic tail and is instrumental in the morphological change of the micelle from spherical to cylindrical micelles. The formed VEF percolated at the backend of a sandpack leading to permeability reduction equivalent to a residual resistant factor of 157 and a breakthrough pressure difference of 671.47 KPa resulting in a 99.3% plugging efficiency. However, the study did not look at the effect of brine chemistry and temperature on the ‘catalytic’ property of CO₂ toward the formulation of stable pseudo-Gemini WLMs. A study dedicated to investigating the effect of pH on the rheological properties of octadecyl trimethylammonium bromide-anthranilic acid complex was conducted. Spectroscopy results revealed that the pH-dependent interaction between the aromatic ring of anthranilic acid and the cationic headgroup resulted in the reversible transition of micelles from Worm-like to spherical, influencing the viscoelasticity. Besides CO₂, organic or nonorganic counterion salts could also influence this transformation between spherical micelles and WLMs. Another potentially challenging issue is the ability to develop gelation via micellar interaction at high temperatures. Recently, a novel Gemini cationic surfactant-based gel originally designed for formation fracturing exhibited tolerance for high temperature as the viscosity was sustained at 25.2 mPa.s after shearing at 200 °C at the rate of 170 s^–1 for 60 min. The behavior was attributed to the reversible micelle self-assembly which translated to repairable qualities even under shear. Under controlled injection regimes, flow tests revealed that this novel material can be a potential formation-plugging agent for CO₂ leakage mitigation.

8.

Depiction of how the morphology of viscoelastic fluid can change from spherical to wormlike micellar.

Zwitterionic surfactants, a variation of Gemini surfactants, have the advantage of minimal adsorption in situ porous rock media partly because they have both anionic and cationic atom groups on the same head. Thus, they are well-suited for subsurface sequestration applications. A couple of studies on zwitterionic-based viscoelastic fluids with a focus on CO₂ responsiveness have been carried out. Gao et al. developed a zwitterionic wormlike micellar complex by blending a base zwitterionic surfactant with an asymmetric bola-type CO₂-sensitive functional group, and a hydrotrope. The suspension at the initial state is a Newtonian fluid with low viscosity, but after coming in contact with CO₂, transforms into a viscoelastic WLMs. The transformation is linked to the protonation of the amine groups on the diamine N,N,2,2-tetramethyl-1,3-propanediamine (TADPA), creating a new zwitterionic specie as depicted in the reaction Scheme below. The creation of the new components is confirmed by NMR and can be explained by the acid/base dissociation degree theory. The novel VEF exhibited stable CO₂ responsiveness up to 363 K and 100 bar. Liu et al. studied the properties of a self-assembly CO₂-responsive WLM formulated with the use of double-tail surfactant (DTS). The novel zwitterionic surfactant could retain a very high viscosity of 100,000 mPa.s up to 120 °C in the presence of CO₂. Conductivity tests revealed that the solution was initially nonionic before CO₂ was added proving that the self-assembly was triggered by protonation, while Cryo-TEM revealed entanglement of cylindrical micelles within the network. The solution was pseudoplastic in the presence of CO₂ with a critical concentration of 80 mM.

1. Reaction of CO₂ with the Amine Functional Group on the TADPA Creates the Zwitterionic Species; R, R′, R′′, and R′′′ are Either Alkyl, Aryl, or H Groups.

The majority of studies on pH-responsive micelles were focused on cationic surfactants, wherein these are synthesized by embedding a pH-stimuli group into the molecular architecture. − Nevertheless, A few anionic surfactant-based viscoelastic WLMs have also been reported in the literature. A novel pH-responsive anionic wormlike micelle was developed using SDES and Na₃PO₄, with morphology transition controlled by pH through ion release. The results revealed that aggregates transformed from spherical micelles to wormlike micelles with high viscosity in the presence of HCl. Here, viscosity improvement is observed to be due to the protonation of ions and the formation of three-dimensional structures by overlapping worm-like micelles as seen in Figure . Furthermore, the addition of NaOH leads to a slight viscosity increase in SDES/Na₃PO₄ solutions. However, under shearing, the WLMs system exhibited thinning-out which can be explained by the alignment in the shear flow direction of elongated WLMs when the shear rate exceeds the critical value. A report on a CO₂-induced anionic wormlike micellar fluid derived by the introduction of a natural anionic surfactant (sodium erucate) stated that When CO₂ was introduced into the aqueous solution, triethylamine was protonated into a quaternary ammonium salt. This facilitates the growth of wormlike micelles due to electrostatic repulsion between the anionic headgroups in NaOEr molecules, resulting in the viscoelasticity buildup. The outcome of the study demonstrated that besides having CO₂-tunable functionalities, , the degree of hydrophobicity can have a significant effect on micellar properties, which also dictates the amount consumable during formulation. The addition of triethylamine improved the system’s response to CO₂ with enhanced pseudoplastic behavior as a function of concentration. In all, the system shows strong viscoelastic properties and stability over a wide temperature range. A major shortcoming of this system is that at low pHs customary for dissolved or supercritical CO₂, the solution will irreversibly become unstable with a low viscosity.

9.

Formation of overlapping wormlike micelles due to protonation of ions in an acidic medium.

Wormlike micelles derived from several types of surfactants including anionic head surfactants, cationic head surfactants, and cationic and anionic pseudo twin-tail gemini surfactants have been tested for CO₂-responsiveness. Tetrametric surfactant-based micelles have also been lately evaluated for possible application in CCUS. A study focused on the CO₂-switchable behavior of a pseudofour-tail surfactant complex formulated by sodium alkyl sulfates and cyclen. The dual twin-tail molecular architecture was made possible by the reaction of stearic acid and cyclen in the presence of CO₂ as demonstrated in Scheme . The CO₂-triggered wormlike micelles’ viscosity increased from 1.2 mPa.s to 3,000 mPa.s. While the study was borne out of the need to use bioenvironmentally friendly materials to reduce CO₂ emissions, the study lacks depth in terms of actual performance in situ subsurface conditions. Most self-assembling micellar systems with CO₂-sensitive functional groups’ responsiveness is instantaneous, forming spherical and cylindrical morphologies. However, the reversible behavior when CO₂ is removed might not be the best reaction for subsurface conformance control applications. Operational-wise, the more desired type of deep reservoir profiling, as far as CO₂ channeling mitigation is concerned, is a more permanent one wherein fractures and high permeability streaks that serve as potential thief zones for CO₂ remain permanently plugged. Therefore, an irreversible gelation after exposure to CO₂ is a more sustainable practice. The prevention of reversibility upon CO₂ withdrawal can be imparted to traditional CO₂-responsive materials by including functional groups that lock-in the gelation of the sealants and inhibit the breakdown and disruption of the rigid structure of the molecular architecture. Likewise, for viscoelastic fluids, these hypothetical inhibiting additives can prevent the reversal of wormlike micellar assemblage to spherical micellar assemblage. A conceptual example of such a system is the dispersion of CO₂-responsive nanogels within a wormlike micellar network. Du et al. exploited the possibility of mixing CO₂-responsive gel particles with CO₂-responsive wormlike micelles to restrain CO₂ breakthrough in subsurface reservoirs. The interaction between the two components was more of a hydrophobic association. The viscosity of the system increased from 10.4 mPa.s to 2339 mPa.s. But unfortunately, the wormlike micelles affected the swellability of the particle gels. This is due to the anionic surfactant sodium p-toluenesulfonate (SPTS) of the micellar compressing the electric double layers of carboxyl groups in the particle gel thereby inhibiting hydrolysis and water-absorbing expansion. Also, the improvement in rheology was reversed when N2 was introduced into the system.

2. Reaction Creates a Pseudo-Four-Tail Surfactant in an Acidic Environment .

^a 1,4,7,10-Tetraazacyclododecane amines are protonated by hydrogen carbonate ions due to the dissolution of CO₂ in aqueous medium. The reversible reaction creates an ionic-stabilized tetrametric surfactant that can be disrupted when CO₂ is removed from the system.

Overall, surfactant-based wormlike micelles’ rheological behavior and viscoelastic tendencies are closely linked to hydrophilic–hydrophobic interactions and ionicity. Here, the determining factors in the formation and variation of micellar morphologies include electrostatic interactions, hydrophobic interactions, and hydrogen bonding. Just as the morphology of the ‘worms’ dictates their mechanical properties, so also is it closely linked to the gelation properties. However, sustainable gelation in situ in the presence of CO₂ can only be attained by a rapid irreversible reaction when H⁺ is released and made available, typical of low pH conditions created by the dissolution of CO₂ in brine. Thus, further studies need to be carried out in designing more smart wormlike micelles in every sense of it; morphologies with functional groups and reaction nodes that are structurally positioned in molecular space to consolidate the already existing attractive-repulsive interactions with hydrogen bonding and possible creation of covalent conjugates or ligand complexes. This way, strong gels that can withstand harsh reservoir conditions of high brine salinity and hardness, high temperature, and unfavorable shear regime can be sustainably propagated in situ.

3.2. Polyelectrolyte Complexes

Although the majority of the studies on CO₂-induced viscoelastic fluids are based on surfactant WLMs, , a few have focused on polymer-derived WLMs systems as well. These are collectively referred to as polyelectrolyte complex (PEC) micelles systems. They are developed by controlled embedding of charged blocks into a polymer’s architecture. By this, several products have been designed for many industries such as drugs, paints, and more relevant to the subject of discussion, adhesives. Thus, for CO₂-sensitive applications, responsive functional groups such as acrylamide are introduced to these blocks. A polymer-based CO₂-triggered smart VEF was designed and synthesized by combining Sodium polyacrylate (NaPAA) and tris (dimethylaminomethyl)­phenol (TAP). In the presence of CO₂, viscoelasticity was imposed on the complex due to the formation of three-dimensional networks in the molecular architecture. This response is traceable to the protonation of tertiary amino groups of TAP to produce quaternary ammonium cations, which form electrostatic binding with the carboxylate of NaPAA. It is interesting to observe that this reversible rheological attribute due to protonation and deprotonation was only obtainable in saline environments. In fact, in the absence of NaCl, the viscosity and elasticity are reduced. This is explained by the electrostatic repulsions and screening of NaPAA chains by the generated quaternary ammonium salts in solution. , This same boost in elasticity and viscosity was also observed after the protonation of amino groups of octadecyl dipropylene triamine (ODPTA) by CO₂. Here, it was confirmed that the vesicles were transformed into wormlike micelles (WLMs). The findings from this study support the previous reports in literature wherein the higher the compositional ratio of the tertiary amine to the carboxylate subgroup on the acrylate functional group, the stronger the protonation, and the better the rheological response. Also, just like it is for most amphiphilic polymeric systems, salinity tends to improve the rheological properties of the system. Redox-mediated RAFT was used to synthesize a series of mono-, di-, and triblocks of PEC. Unlike previous studies in literature, these PECs were observed to form viscoelastic gels at relatively low concentrations. The mechanism of their micellar aggregation is traceable to complex ionic coacervation in solution. Although the outcome rheological behavior is affected by the shear regime, pH, and salinity of the solution, this is still a strong function of concentration, and the morphology of the micellar architecture, as well as its hydrodynamic size. Another factor is the stoichiometric charge ratio across the PEC network which could affect, not only the rheology but also the stability of the micellar solution.

A more structurally stable PEC can be formulated by embedding them into the CO₂-responsive network surfactants and nanoparticles. Of such is Liu et al’s work where they formulated a gel using 0.8% polyethylenimine (PEI), 0.8% sodium dodecyl sulfate (SDS), and 0.1% nanosilica. In addition to the cross-linking and CO₂-responsiveness capabilities of PEI, the SDS provides both ionic and hydrophobic interactions which is essential for a strong micellation. While the silica nanoparticles provided structural stability. Thus, the resultant gel could attain thickening and self-healing behavior at conditions up to 90 °C and 20,000 mg/L. In addition, the gel system could influence a plugging efficiency exceeding 95% in medium-permeability artificial cores. For the sake of environmental sustainability in the application of sealants for CO₂ leakage control, biobased wormlike micellar solutions could be considered as well. Wu and colleagues studied the formation plugging capabilities of a carboxymethyl chitosan grafted copolymer. The self-assemblage behavior is thermally dictated and forms mesoporous aggregated structures at thermal conditions above the lower critical solution temperature (LCST). Although the micellar aggregation is reversible, the LCST can be tuned by modifying the molar content of the functional groups on the polymeric chains. The nanomicelle-derived gel could effectively plug low permeability cores via varying mechanisms in situ as depicted in Figure . In terms of gelation, more studies should look into polysaccharide-derived polyelectrolyte complexes since they naturally have swellability tendencies in aqueous phases. An attempt to address the reversibility of CO₂ responsiveness, which does not benefit their sequestration, was made when dimethylaminopropyl methacrylamide (DMAPMAm) was grafted onto the backbone of sodium carboxymethyl cellulose and characterized rheologically. In the semidilute entangled regime, the copolymer suspension’s CO₂-dictated gelation exhibited partial irreversibility at a temperature of 60 °C. This unique behavior is attributable to the high initial CO₂ dissociation constant in the protonation of the amine group on the DMAPMAm. Hence, the poor deprotonation when CO₂ is removed from the medium. Also, this may be linked to the several complex interactions between the CO₂-sensitive DMAPMAm graft and the anhydroglucose unit backbone which promotes the absorption of CO₂ molecules within the network. Thus, it could be inferred that any chemical reaction that supports the withholding of the actual CO₂ molecules within the gel will resist the release, even in the presence of inert gases, and high temperature.

10.

Carboxymethyl chitosan grafted copolymer CCMMA has different plugging mechanisms for micropores at conditions above and below critical points as dictated by chemical structure and interaction with rock grains. Reprinted from Wu et al. “Development and Characterization of Thermoresponsive Smart Self-Adaptive Chitosan-Based Polymer for Wellbore Plugging.” Copyright Polymers 2023, 15, 4632. (https://creativecommons.org/licenses/by/4.0/).

Aside from the blockage of potential pathways of escape of injected CO₂ for possible sequestration, another way by which CO₂ can be trapped in the subsurface permanently is by viscosification. This could be done either in situ or by coinjection of CO₂ with the viscosifying agent. Studies have revealed that this could be adaptable to both subcritical and supercritical CO₂ injection. Furthermore, CO₂-responsive polymer-based gels with wormlike micellar configurations are the most suited for this technique since the swelling and sealing properties are enhanced in the presence of CO₂. Ding et al’s work demonstrated that with a low concentration of viscosifying agent, the mobility control of CO₂ within the reservoir can be considerably enhanced, thereby increasing the storage capacity therein. Their study demonstrated that the viscosification of CO₂ contributed to its increased saturation, displacement of resident brine, and overall trapping. Here also, the effect of the viscosification was evident in the stabilization of the displacement front as detected by fractional flow analysis and X-ray CT imaging in layered core samples. Figure shows how the CO₂ saturation distribution pattern in layered cores is well-defined after thickening. The study proved that if low-concentration oligomers could attain a 50% increment in CO₂ storage capacity in heterogeneous formations, how much more high-weighted CO₂-responsive WLMs. Nevertheless, in the context of viscoelasticity, while surfactant-based wormlike micelles can easily form different morphological structures which translate to interesting rheological outlooks, the chemistry of polymers better allows the modification of PECs, ultimately having the advantage of being easily infused with CO₂-responsive functional groups for gelation. More studies should look into this. Finding alternative CO₂-sensitive functional groups besides amine, that could help in developing stronger and more lasting sol–gel materials with less tendency for reversible swelling should be top-priority research.

11.

Spatiotemporal distribution of CO₂ saturation injected into layered core samples before viscosification (left) and after viscosification (right). The blue dots stand for brine saturation distribution while the red dots for CO₂. Before viscosification, CO₂ displacement is characterized by poor shock fronts and massive underside bypass which could lead to early breakthrough. However, after viscosification, the displacement front is more stable and well-defined. Adapted from Ding et al. “CO2 Trapping in Layered Porous Media by Effective Viscosification.” Copyright Water Resources Research 2024, 60.

4.0. Conclusions

This literature review came up in light of the limitations of conventional Cementous materials, and both organic and inorganic polymeric materials, to uphold the integrity of CO₂ storage in subsurface formations. In particular, the inabilities of these materials to either prevent, or to remediate the leakage of CO₂ at the wellbore, from the reservoir into the connecting aquifer, and from the reservoir to the near-surface environment via the caprock. Hence, this review was designed as an attempt to search for possible replacements for conventional sealing materials. With the performance and shortfall of the previous materials in mind, this latest review takes a deep dive and a broad look at augmented polymeric systems, also known as interpenetrating polymeric network gels and viscoelastic fluids as potential materials for CO₂ containment in the subsurface geostorage sites. As summarized in Table , the subcategories of these materials were critically evaluated in terms of their mechanical and thermal stability, plugging power, rheological behavior, tolerance to harsh brine conditions, and most importantly, response when they come in contact with CO₂. The review revealed that Interpenetrating polymer networks can enhance the mechanical strength and tolerance of gels to harsh subsurface conditions where CO₂ is stored. Nanoparticles can also be embedded in multinetwork polymer systems, either in dispersed form or as cross-linkers, to further improve the structural integrity of the molecular architecture of gels. Likewise, well-designed viscoelastic fluids, such as wormlike and polyelectrolyte micellar suspensions, have the potential to plug heterogeneous reservoirs where CO₂ is stored because of their rheological and swelling properties in the presence of CO₂. From another perspective, the review also revealed that the adhesive properties of these potential sealants, sustainable in situ plugging, and characteristics of the fracture network are equally important to the success of the leakage remediation project.

1. Overview of the New Family of Gels, Their Properties, and Characteristics.

	performance indicators
gel type	CO2–responsiveness	material strength	salinity sensitivity	rheology	plugging capacity	remarks
IPN gels	tunable/reversible swellability if the network contains protonable functional groups	self-healable properties can be induced via a targeted molecular design of the multinetwork	better tolerance to harsh brine conditions compared to normal polymer gels	enhanced viscosity and gelation compared to single cross-linked polymer networks	enhanced plugging over regular polymer gels	reduced injectivity with potentials of fracking during injection.Nonsustainable self-healing properties at harsh reservoir conditions
nanoparticle-reinforced gels	CO2-responsiveness not traceable to nanoparticles	boosted mechanical properties	pH sensitive; improved tolerance to salinity	enhanced rheology	improved plugging capacity	potentially expensive; control of nanoparticle distribution within a polymer network is a challenge; mostly affected by brine hardness.
WLMs	CO2-responsiveness with tunable swellability	self-healing attributes can be easily incorporated	salt-aided aggregations; micellar morphology is dictated by types of ions	viscous and elastic properties are weak compared to regular polymer gels	moderate plugging power; there is room for improving the plugging efficiency via molecular design	nonfeasibility of in situ hardening and sealing
PECs	amine-containing PECs demonstrate reversible CO2-responsiveness	easily affected by shear	performance is dependent on salt type and concentration	improved rheology as a function of the combination of electrostatic forces, hydrophobic–hydrophilic interactions, and protonation/deprotonation	plugging is limited to low-permeability formation	weak adhesive properties; might not be suitable for the sealing of fractures and large cracks

5.0. Recommendations for Future Research

The utilization of viscoelastic fluids for CO₂ subsurface sealing and conformance control, either in the form of wormlike micellar or polyelectrolyte complexes, is still very ‘green’ and holds a lot of potential. While studies on them, as regards other spheres of industry, may exist in the literature, those targeting CO₂ storage are very limited. The fact that these materials can attain the much-desired rheological behaviors via the combination of multiple mechanisms when they come in contact with CO₂, such as protonation and micellar aggregation, makes them objects of much interest. However, further investigations need to be conducted outside the swelling kinetics, viscosity, and elasticity to assess and understand them. As plugging agents for subsurface applications, realistic research questions like their ability to seal fractures and communicating streaks while inducing mechanical stability in situ need to be addressed. A targeted approach to this research theme is looking at the microchemistry of sealants’ adhesive action on rock surfaces. The fundamental understanding of how solid surfaces bind permanently can help in the design of a new family of viscoelastic sealants incorporated with elastomeric functional groups that promote rapid reaction with rock minerals in the presence of CO₂ in the subsurface environment. In the same vein, extended studies on the sol–gel attributes during interaction with rocks will shed more light on their ability to alter the heterogeneity of geologic formations.

The design of porous materials based on the IPN concept has received a lot of attention recently. This concept can be extended to developing super absorbent polymers for CO₂ with a high tendency for swelling because of their CO₂-philicity, making the porous IPNs easily fill fractured pathways susceptible to leaking. This way, the CO₂ barrier and conformance control are improved. The synthesis procedure can introduce a high degree of compactness across the interpenetrating network, potentially enhancing leak prevention in subsurface media targeted for sequestration. In the same vein, multilayers of polar and nonpolar polymers, either semipenetrating, fully penetrating, or just blends, are very good options for stability and mechanical strength in addition to the needed barrier properties. The complexity of designing and synthesizing multicomponent multiphase polymer systems for subsurface CO₂ storage applications will demand the incorporation of machine learning-assisted numerical modeling and simulation to be able to predict the rheological, chemical, and mechanical behaviors and properties of these polymer systems accurately. This should be in two folds: first is the understanding of the properties, interactions, and responses at atomistic scales using tools like molecular simulations and quantitative structure–property relationships. Second, computational modeling of the injection and displacement of the sealants at the core and field scale to capture the performance in situ, using data from molecular studies. This will not only aid in closely correlating the microstructure of the proposed polymer systems with the mechanical properties and performance, but it will also eliminate the differing reports on the properties of polymer composites. The majority of IPNs available, commercially and otherwise, are developed using synthetic materials that are considered a risk, and hazardous, to human health and environmental safety. Therefore, there is a renewed interest in the development of biopolymer-based IPNs for CCUS applications. It cannot be overemphasizing the need to adopt more environmentally friendly materials for the design of polymeric mixtures. For instance, the incorporation of naturally derived nanofillers such as nanocellulose particles has recently captured a lot of interest. Since these stabilizers are byproducts or wastes from agro-industry activities, the process is not only cheap but environmentally sustainable.

It is believed that the homogeneous dispersion of impermeable lamellar nanofillers can significantly increase the barrier properties of nanoreinforced polymer composites against the migration and diffusion of gases such as CO₂. Likewise, the failure of these composite materials in situ is traceable to the problem of inhomogeneous dispersion of nanoparticles in polymer matrices. The lack of uniform distribution within the phases in the polymer network is more of a shortfall in the techniques of preparation and mixing. In the context of performance, a key factor in the ability to seal and plug leakage pathways is the orientation of the nanoparticles. Therefore, an interesting research theme would be exploiting different nanoparticle orientations, alignment, morphology, and aggregations to enhance plugging abilities in fractured porous media, especially to prevent CO₂ migration. Thus, more studies are needed to understand how to control the dispersion, orientation, and alignment of nanoparticles. Nanoclays are a very efficient reinforcing filler in many polar polymer matrices, and they hold a lot of promise in formation sealing because of their ability to swell. However, more studies need to be carried out on how it can be effectively incorporated into the polymer matrices. Also probing investigations on their CO₂ responsiveness is essential.

Glossary

Nomenclature

3D

three dimensional

AFAPE-20

acryloyl fatty alcohol polyoxyethylene ether

AIPNG

alginate-based interpenetrating polymer hydrogel

AM

acrylamide

AMPS

2-acrylamido-2-methylpropanesulfonic acid

ANOVA

analysis of variance

ANN

artificial neutral network

APS

ammonium persulfate

B-PEI

branched-polyethylenimine

CAT-AN

cation–anion

CCMMA

carboxymethyl chitosan grafted poly­(oligoethylene glycol) methyl

CCUS

carbon capture, utilization, and storage

CO₂

carbon dioxide

CPNPs

cement-based porous nanoparticles

CR-PPG

CO₂-responsive preformed particle gel

Cryo-TEM

cryogenic transmission electron microscopy

DETA

diethylenetriamine

DFT

density functional theory

DMAPMAm

dimethylaminopropyl methacrylamide

DMAEMA

(2-dimethylaminoethyl)­methyl-acrylate

DNWR

double network water-absorbent resin

DPG

dispersed particle gels

DSC

differential scanning calorimetry

DTS

double-tail surfactant

EADP

erucic acid 3-(N,N-dimethylamino)­propylamide

EDTA4–4Na⁺

ethylenediaminetetraacetic acid tetrasodium

EOR

enhanced oil recovery

FV

fracture volume

GHG

greenhouse gases

HCl

hydrochloric acid

HPAM

partially hydrolyzed polyacrylamide

IPCC

Intergovernmental Panel on Climate Change

IPN

interpenetrating polymer network

KPa

kiloPascal

LCST

lower critical solution temperature

MA

maleic acid

MBA/MBAA

N,N′-methylene bis-acrylamide

Mg/L

milligram per liter

MJm-2

megajoules per square meter

mM

millimoles

MPa

megaPascal

mPa.s

milliPascal seconds

NaCl

sodium chloride

Na3PO4

sodium phosphate

NaOEr

sodium erucate

NaPAA

sodium polyacrylate

NC

nanoclay

NETL

National Energy Technology Laboratory

NMR

nuclear magnetic resonance

NPG

nanocellulose-regulated particle gel

ODPTA

octadecyl dipropylene triamine

PAM

polyacrylamide

PCA

principal component analysis

PEC

polyelectrolyte complex

PEI

polyethylenimine

PMS

potassium methylsilanetriolate

poly­(AM-co-VA)

acrylamide-vinyl acetate copolymer

PPG

preformed particle gel

PVOH

poly­(vinyl alcohol)

PVI

pore volume injected

R-80-HMTA-PADC

resorcinol-hexamethylenetetramine-polyacrylamide dimethyldiallyl ammonium chloride amphiphilic gel

RAFT

reversible addition–fragmentation chain transfer

REDOX

reduction–oxidation

RRF

residual resistance factor

RSM

response surface methodology

SDES

sodium dodecyl ether sulfate

SDS

sodium dodecyl sulfate

SEM

scanning electron microscopy

SiO2

silicon oxide

SPTS

sodium p-toluenesulfonate

SVM

support vector machines

TADPA

N,N,2,2-tetramethyl-1,3-propanediamine

TAP

tris­(dimethyl aminomethyl)­phenol

TEA

triethylamine

UTCHEM

University of Texas Chemical Flooding Simulator

UV–vis

visual ultra-violet spectroscopy

VEF

viscoelastic fluids

VSNPs

vinyl silica nanoparticles

WLMs

wormlike micelles

WSPR

water-soluble phenolic resin

Biographies

Funsho Afolabi is a postdoctoral research fellow in the Department of Chemical Engineering at Universiti Malaya, Malaysia. Before this appointment, he was a research scientist at the Centre of Reservoir Dynamics, Universiti Teknologi PETRONAS. His domain of research is in carbon capture and underground storage, and utilization for enhanced oil recovery. He specializes in the design, synthesis, and deployment of functional polymers and surfactants for improved/enhanced oil recovery, production enhancement, and CO₂ storage purposes. He has also worked on projects related to sand control management using chemical agglomeration methods. Prior to his research fellowships at Universiti Malaya and Universiti Teknologi PETRONAS, he lectured for several years at Afe Babalola University, Ado Ekiti (ABUAD) Nigeria, handling petroleum engineering modules in reservoir engineering, production engineering, and drilling engineering. He has a BSc degree in Industrial Chemistry (University of Ilorin, Nigeria), an MSc in Petroleum Engineering (University of Ibadan, Nigeria), and a PhD in Petroleum Engineering (Universiti Teknologi Petronas, Malaysia).

Iskandar Dzulkarnain is a faculty member in the Petroleum Engineering Department and currently Head of the Centre of Reservoir Dynamics (CORED), one of the research centers under the Institute of Sustainable Energy & Resources, Universiti Teknologi PETRONAS (UTP). The center focuses on studies related to subsurface dynamics for hydrocarbon recovery and geo-sequestration. He obtained his Ph.D in Petroleum Engineering from Louisiana State University (LSU), USA in 2018, and prior to that graduated with an MSc in Petroleum Engineering from the joint Heriot-Watt and UTP program (2010) and Bachelor of Engineering (Hons.) Electrical and Electronics Engineering from UTP in 2007. He has experience teaching reservoir engineering-related courses at the graduate & undergraduate level. He is also the project leader for various research and consultancy projects related to EOR, CCUS, and reservoir production enhancement.

Syed M. Mahmood, P.E. graduated as a Petroleum Engineer from Stanford University and has over 40 years of professional experience in the oil & gas industry including field operations, research, and academics that includes over 15 years of waterflooding and EOR teaching experience among others. Currently serving as Associate Professor at University Teknologi PETRONAS involved in teaching and research in various areas of secondary and tertiary oil recovery and flow assurance.

Fahd Alakbari is a postdoctoral researcher at the Interdisciplinary Research Center for Hydrogen Technologies and Carbon Management at King Fahd University of Petroleum & Minerals, Saudi Arabia. He completed his Ph.D. degree in petroleum engineering from Universiti Teknologi PETRONAS, Malaysia. His research focuses on applying machine learning, statistical methods, and modeling techniques to engineering problems, carbon storage, optimizing drilling fluids, and managing sand production.

F.A. performed conceptualization, original draft, methodology, editing, and analysis; I.D. performed conceptualization, review and editing, analysis, project management, resource gathering, and funding acquisition; S.M.M. performed writing–review; F.S.A. performed writing–review and editing; S.K. performed project management and funding; J.H.L. performed writing–review; A.G. performed writing–review; M.S.K. performed writing–review.

The authors declare no competing financial interest.