The conventional production technique employed for low-permeability tight reservoirs exhibits limited productivity. To solve the problem, an acetate-type supercritical carbon dioxide (scCO₂) thickener, PVE, which contains a large number of microporous structures, was prepared using the atom transfer radical polymerization (ATRP) method. The product exhibited an ability to decrease the minimum miscibility pressure of scCO₂ during a solubility test and demonstrated a favorable extraction efficiency in a low-permeability tight core displacement test. At 15 MPa and 70 °C, PVE-scCO₂ at a concentration of 0.2% exhibits effective oil recovery rates of 5.61% for the 0.25 mD core and 2.65% for the 5 mD core. The result demonstrates that the incorporation of the thickener PVE can effectively mitigate gas channeling, further improve oil displacement efficiency, and inflict minimal damage to crude oil. The mechanism of thickening was analyzed through molecular simulation. The calculated trend of thickening exhibited excellent agreement with the experimental measurement rule. The simulation results demonstrate that the contact area between the polymer and CO₂ increases in direct proportion to both the number of thickener molecules and the viscosity of the system. The study presents an effective strategy for mitigating gas channeling during scCO₂ flooding and has a wide application prospect.

Under the influence of the sedimentation process, the phenomenon of intraformational non-homogeneity is widely observed in low-permeability reservoirs. In the development process of water and gas replacement (WAG), the transport law of water and gas and the distribution of residual oil are seriously affected by the non-homogeneity of reservoir properties. In this paper, a study on two types of reservoirs with certain lengths and thicknesses is carried out, and a reasonable development method is proposed according to the characteristics of each reservoir. Firstly, through indoor physical simulation experiments combined with low-field nuclear magnetic resonance scanning (NMR), this study investigates the influence of injection rate and core length on the double-layer low-permeability inhomogeneous core replacement and pore throat mobilization characteristics. Then, a two-layer inhomogeneous low-permeability microscopic model is designed to investigate the model’s replacement and pore throat mobilization characteristics under the combined influence of rhythmites, gravity, the injection rate, etc. Finally, based on the results of the core replacement and numerical simulation, a more reasonable development method is proposed for each type of reservoir. The results show that for inhomogeneous cores of a certain length, the WAG process can significantly increase the injection pressure and effectively seal the high-permeability layer through the Jamin effect to improve the degree of recovery. Moreover, for positive and reverse rhythm reservoirs of a certain thickness, the injection rate can be reduced according to the physical properties of the reservoir, and the gravity overburden phenomenon of the gas is used to achieve the effective development of the upper layers. The effect of the development of a positive rhythm reservoir therefore improved significantly. These findings provide data support for improving the development effectiveness of CO₂ in low-permeability inhomogeneous reservoirs and emphasize the importance of the influence of multiple factors, such as injection flow rate, gravity, and rhythm, in CO₂ replacement.

Carbon dioxide (CO₂) drive is one of the effective methods to develop old oil fields with high water content for tertiary oil recovery and to improve the recovery rate. However, due to the low viscosity of pure CO₂, it is not conducive to expanding the wave volume of the mixed phase, which leads to difficulty utilizing the residual oil in vertical distribution and a low degree of recovery in the reservoir. By introducing viscosity enhancers, it is possible to reduce the two-phase fluidity ratio, expanding the degree of longitudinal rippling and oil recovery efficiency. It has been proven that the acetate scCO₂ tackifier PVE can effectively tackify CO₂ systems. However, little research has been reported on the microscopic viscosity enhancement mechanism of scCO₂ viscosity enhancers. To investigate the influence of a vinyl acetate (VAc) functional unit on the viscosity enhancement effect of the CO₂ system, PVE (Polymer–Viscosity–Enhance, P-3) was used as the parent, the proportion of VAc was changed, and the molecules P-1 and P-2 were designed to establish a molecular dynamics simulation model for the P-n-CO₂ system. The molecules in the system under the conditions of 70 °C-10 MPa, 80 °C-10 MPa, and 70 °C-20 MPa were simulated; the viscosity of the system was calculated; and the error between the theoretical and simulated values of the viscosity in the CO₂ system was relatively small. The difference between P-n molecular structure and system viscosity was analyzed at multiple scales through polymer molecular dynamics simulations and used the molecular radial distribution function, system density, accessible surface area, radius of gyration, minimum intermolecular distance, and minimum number of intermolecular contacts as indicators. This study aimed to elucidate the viscosity enhancement mechanism, and the results showed that the higher the proportion of VAc introduced into the molecules of P-n-scCO₂ viscosities, the larger the molecular amplitude, the larger the effective contact area, and the greater the viscosity of the system. Improvement in the contact efficiency between the ester group on the P-n molecule and CO₂ promotes the onset of solvation behavior. This study on the microscopic mechanism of scCO₂ tackifiers provides a theoretical approach for the design of new CO₂ tackifiers.

Since reservoirs with permeability less than 10 mD are characterized by high injection difficulty, high-pressure drop loss, and low pore throat mobilization during the water drive process, CO₂ is often used for development in actual production to reduce the injection difficulty and carbon emission simultaneously. However, microfractures are usually developed in low-permeability reservoirs, which further reduces the injection difficulty of the driving medium. At the same time, this makes the injected gas flow very fast, while the gas utilization rate is low, resulting in a low degree of recovery. This paper conducted a series of studies on the displacement effect of CO₂-soluble foaming systems in low-permeability fractured reservoirs (the permeability of the core matrix is about 0.25 mD). For the two CO₂-soluble blowing agents CG-1 and CG-2, the effects of the CO₂ phase state, water content, and oil content on static foaming performance were first investigated; then, a more effective blowing agent was preferred for the replacement experiments according to the foaming results; and finally, the effects of the blowing agents on sealing and improving the recovery degree of a fully open fractured core were investigated at different injection rates and concentrations, and the injection parameters were optimized. The results show that CG-1 still has good foaming performance under low water volume and various oil contents and can be used in subsequent fractured core replacement experiments. After selecting the injection rate and concentration, the blowing agent can be used in subsequent fractured cores under injection conditions of 0.6 mL/min and 2.80%. In injection conditions, the foaming agent can achieve an 83.7% blocking rate and improve the extraction degree by 12.02%. The research content of this paper can provide data support for the application effect of a CO₂-soluble blowing agent in a fractured core.

This study investigates the use of fly ash to mitigate the long-term performance degradation of Portland cement-based sealing materials in high-salinity environments, such as those found in gas storage reservoirs. We systematically evaluated the evolution of material properties under different temperatures and curing periods. Our integrated methodology combining mechanical tests, microstructural analysis, and chloride migration assessment, reveals a multi-faceted mechanism by which fly ash enhances chloride resistance. The key findings demonstrate that reactive Al₂O₃ in fly ash promotes the formation of Friedel’s salt, increasing chemical chloride binding and reducing the chloride ingress rate in the Portland cement–Fly ash system (PFS) to only 26.6% of that in the Portland Cement system (PCS). Concurrently, the pozzolanic reaction consumes portlandite (Ca(OH)₂), forming stable C-A-S-H gel and refining the pore structure by filling interconnected channels. This nanoscale pore refinement decreased permeability by nearly an order of magnitude. After 90 days of curing in 90 °C saline solution, PFS achieved a compressive strength of 28.2 MPa and maintained an exceptionally low internal chloride content of 0.08 wt.%, demonstrating superior long-term durability. This work clarifies the synergistic mechanisms of fly ash modification and temperature effects, providing a theoretical basis for optimizing sealing materials for deep geological reservoirs and experimental support for the application of fly ash in high-temperature, high-salinity engineering environments.

This study investigates the protective performance of a triazole-based Mannich base corrosion inhibitor, 4-((1,2,4-triazolyl)methyl) dibutylamine (TZMBA), on P110 carbon steel in dissolved oxygen environments. TZMBA was synthesized via a Mannich reaction, and its molecular structure was confirmed by Fourier transform infrared spectroscopy (FT-IR). The corrosion inhibition behavior and underlying mechanisms were systematically explored through weight loss measurements, surface characterization, and multiscale molecular simulations. Weight loss results indicated that TZMBA significantly mitigates the corrosion of P110 steel, with inhibition efficiency reaching 81.5% at 1.67 mmol/L and 82.0% at 2.14 mmol/L. Adsorption thermodynamic analysis revealed that the process follows the Langmuir isotherm model. The calculated standard Gibbs free energy ${∆G}_{ads}^0$ of −38.69 kJ/mol suggests a spontaneous, mixed-type adsorption mechanism involving both physisorption and chemisorption. Scanning electron microscopy (SEM) observations confirmed a marked reduction in surface degradation, characterized by suppressed corrosion products and minimized localized attack. X-ray photoelectron spectroscopy (XPS) further verified that TZMBA anchors to the metal surface through chemical coordination, forming a robust organic-inorganic composite film. From a theoretical perspective, frontier molecular orbital (FMO) analysis showed that TZMBA’s high E_HOMO and narrow energy gap facilitate efficient electron transfer. Combined Fukui function and molecular electrostatic potential (MEP) maps identified the nitrogen atoms in the triazole ring and amine group as the primary active sites. Furthermore, molecular dynamics (MD) simulations demonstrated that TZMBA molecules adopt a nearly parallel configuration on the Fe surface. The high negative interaction energy obtained from MD simulations confirms a strong binding affinity and a potent inherent driving force for the formation of a stable protective layer. Overall, the integration of experimental data and theoretical calculations establishes TZMBA as an effective inhibitor that provides superior protection by forming a stable, compact adsorption film on P110 carbon steel.