Bin Xu

Gel materials are widely used in underground mining for air leakage sealing and coal spontaneous combustion prevention. In this study, a novel self-healing carboxymethyl cellulose-modified amphiphilic polymer hydrogel with fire prevention and extinguishing capabilities is synthesized through ionic crosslinking between CMC-graft-poly(AM-co-NaA-co-BAM) and aluminum citrate (AlCit). The copolymer is constructed by grafting sodium carboxymethyl cellulose (CMC) onto an amphiphilic polymer backbone composed of acrylamide (AM), sodium acrylate (NaA), and N-benzylacrylamide (BAM), forming a dual-network structure via hydrophobic association and hydrogen bonding. The carboxymethyl cellulose-modified amphiphilic polymer demonstrates optimal viscosity-enhancing performance at a CMC content of 7.5 wt%. CMC-graft-poly(AM-co-NaA-co-BAM) demonstrated superior temperature, shear, and salt resistant performance compared with poly(AM-co-NaA-co-BAM), poly(AM-co-NaA), and CMC polymers, as well as enhanced viscoelasticity and self-healing capability. When crosslinked with AlCit, CMC-graft-poly(AM-co-NaA-co-BAM)-AlCit gel demonstrated superior viscoelastic properties and self-healing capability, as well as thermal stability, which gave the superior fire prevention and extinguishing performance for charcoal in fire extinction tests. CMC-graft-poly(AM-co-NaA-co-BAM) has abundant cross-linking sites, which lead to accelerated gelation and improved mechanical strength, while the hydrophobic microdomains acted as physical cross-linking points that interconnected polymer chains into a three-dimensional network. The hydrophobic interactions within the hydrogel are dynamically reversible. This intrinsic property allows physical cross-links to spontaneously reassociate when fracture surfaces make contact. Consequently, the material exhibits autonomous self-healing.

Due to the widespread heterogeneity in oil reservoirs and severe water channeling, hydrogel-based agents are employed for profile control and water plugging. Amphiphilic polymers exhibit superior temperature and salt tolerance, and gels formed with these polymers as the primary agent demonstrate enhanced stability, showing broad application prospects. The ternary copolymer P(AM-NaA-ODAM) was synthesized via free-radical solution polymerization, with structural characterization of the product and related monomers performed using infrared spectroscopy. Leveraging the excellent properties of the P(AM-NaA-ODAM) solution, it was utilized as the main agent to construct the gel. The crosslinker formulation was optimized via a single-factor method, with gelation time and gel strength serving as key indicators to determine the optimal composition: hexamethylenetetramine (0.3%), resorcinol (0.05%), and citric acid (0.3%). Furthermore, under this optimized formulation, the effects of temperature and salinity on the amphiphilic polymer gel system were investigated, identifying suitable conditions for stable gel performance and providing a theoretical basis for oilfield profile control and water plugging operations.

Water well profile control is the main way to control water channeling in low-permeability fractured reservoirs, and preformed particle gels (PPGs) are commonly used. A preformed particle gel was prepared and the synthesis conditions were optimized. The temperature and salt resistant performance, plugging performance were investigated and the field application was tested. The results showed PPGs exhibited good temperature and salt resistant performance. PPGs with larger particle size showed greater plugging strength but shorter valid period. Field tests suggested that multiple rounds of profile control should be employed using PPGs with different particle sizes to achieve deep profile control.

Delayed crosslinking polymer gel systems are widely utilized in deep profile control processes for water production control in oilfields. In this paper, a kind of delayed crosslinking amphiphilic polymer gel system with adjustable gelation time based on competitive inclusion was prepared and its delayed crosslinking gelling properties were studied. The amphiphilic polymer of P(acrylamide (AM)–sodium acrylate (NaA)–N-dodecylacrylamide (DDAM)) was synthesized and it showed much better salt resistance, temperature resistance, and shear resistance performance compared with hydrolyzed polyacrylamide (HPAM). Phenol can be controlled released from the the cavity of β-cyclodextrin (β-CD) ring in the presence of the hydrophobic group used as the competitive inclusion agent in the amphiphilic polymer backbone. Accordingly, the gelation time of the delayed crosslinking amphiphilic polymer gel system is closely related to release rate of the crosslinker from the the cavity of β-CD ring. This study screened an amphiphilic polymer with good salt resistance and temperature resistance performance, which can be used in high temperature and high salinity reservoirs, and provided a feasible way to control the gelation time of the polymer gel system by the competitive inclusion method.

Wax deposition is harmful to oil wells, especially for waxy heavy oils at low temperature. The influencing factors on wax deposition of heavy oil were studied and a kind of O/W emulsion type wellbore wax remover was investigated. The results showed that the wax deposition rate of Jinghe heavy oil increased with the increasing wax content and asphaltenes content but decreased with the increasing water content. The oil in water emulsion type paraffin remover was prepared and it showed both good wax dissolution and paraffin prevention ability and can save large quantities of solvent. The results of this study provides a possible way for waxy heavy oils to dissolve wax, to prevent wax deposition and reduce the viscosity of heavy oils by emulsification together, which is helpful to reduce the frequency of hot washing and enhance oil recovery for waxy heavy oils.

Miscible CO₂ injection process has become widely used technique for the enhanced oil recovery in low permeability reservoirs. Core flooding experiments and field test of CO₂ miscible flooding in low permeability sandstone reservoirs and its influence on crude oil properties was studied. The results showed that CO₂ miscible flooding in low permeability sandstone reservoirs can enhance oil recovery both in laboratory study and field test. The permeability of sandstone reservoirs decreased during CO₂ miscible flooding due to the precipitation of asphaltene of crude oil. The precipitation of asphaltene lead to a reduction of asphaltene content and the apparent viscosity of crude oil. A further study on inhibitors and removers for asphaltene deposits from crude oil should be investigated to prevent and remove asphaltene deposits in low permeability sandstone reservoirs.

Hydrophobically modified polyacrylamides can be used to enhance oil recovery in tertiary oil recovery process because they have good thickening and emulsification properties. Hydrophobically modified polyacrylamides with different hydrophobic groups were synthesized using micellar polymerization. Above CAC, elastic polymer gel is formed by the aggregation of hydrophobic groups. Hydrophobicity of hydrophobic groups plays a substantially important role in properties of HMPAMs solutions. Higher hydrophobicity of hydrophobic groups leads to more intensive intermolecular association and thus helps to enhance the apparent viscosity of HMPAMs solutions and form stronger elastic polymer gel network structures in HMPAMs solutions which can enhance the stability of the O/W crude oil emulsions stabilized by HMPAMs.