With the application of CO₂ fracturing, CO₂ huff and puff, CO₂ flooding, and other stimulation technologies in shale reservoirs, a large amount of CO₂ remained in the formation, which also lead to the serious corrosion problem of CO₂ in shale reservoirs. In order to solve the harm caused by CO₂ corrosion, it is necessary to curb CO₂ corrosion from the cementing cement ring to ensure the long-term stable exploitation of shale oil. Therefore, a new latex was created using liquid polybutadiene, styrene, 2-acrylamide-2-methylpropanesulfonic acid, and maleic anhydride to increase the cement ring’s resistance to CO₂ corrosion. The latex’s structure and characteristics were then confirmed using infrared, particle size analyzer, thermogravimetric analysis, and transmission electron microscopy. The major size distribution of latex is between 160 and 220 nm, with a solid content of 32.2% and an apparent viscosity of 36.8 mPa·s. And it had good physical properties and stability. Latex can effectively improve the properties of cement slurry and cement composite. When the amount of latex was 8%, the fluidity index of cement slurry was 0.76, the consistency index was 0.5363, the free liquid content was only 0.1%, and the water loss was reduced to 108 mL. At the same time, latex has a certain retarding ability. With 8% latex, the cement slurry has a specific retarding ability, is 0.76 and 0.5363, has a free liquid content of just 0.1%, and reduces water loss to 108 mL. Moreover, latex had certain retarding properties. The compressive strength and flexural strength of the latex cement composite were increased by 13.47% and 33.64% compared with the blank cement composite. A long-term CO₂ corrosion experiment also showed that latex significantly increased the cement composite’s resilience to corrosion, lowering the blank cement composite’s growth rate of permeability from 46.88% to 19.41% and its compressive strength drop rate from 27.39% to 11.74%. Through the use of XRD and SEM, the latex’s anti-corrosion mechanism, hydration products, and microstructure were examined. In addition to forming a continuous network structure with the hydrated calcium silicate and other gels, the latex can form a latex film to attach and fill the hydration products. This slows down the rate of CO₂ corrosion of the hydration products, enhancing the cement composite’s resistance to corrosion. CO₂-resistant toughened latex can effectively solve the CO₂ corrosion problem of the cementing cement ring in shale reservoirs.

Low-salinity water flooding is a commonly used method to enhance oil recovery. At the microscopic scale, changes in pore structure and the distribution of remaining oil are critical to the effectiveness of water flooding. However, current research on the relationship between pore structure and remaining oil distribution is relatively limited. Therefore, this study employed micro-CT technology to analyze changes in pore structure and the distribution characteristics of remaining oil in sandstone cores during the water flooding process. Micron CT technology provides non-destructive, high-resolution three-dimensional imaging, clearly revealing the dynamic changes in the oil-water interface and remaining oil. The experiments included water saturation, oil saturation, and multi-stage water displacement processes in sandstone cores with different permeability values. The results show that the oil saturation in the rock core decreases during water flooding, and the morphology of remaining oil changes with increasing water flooding volume: cluster-like remaining oil decreases rapidly, while porous and membrane-like remaining oil gradually transforms, and columnar and droplet-like remaining oil increases under specific conditions. The study results indicate that at 1 PV flooding volume, the crude oil recovery rate reaches 57.56%; at 5 PV, the recovery rate increases to 64.00%; and at 100 PV, the recovery rate reaches 75.53%. This indicates that water flooding significantly improves recovery rates by enhancing wettability and capillary forces. Meanwhile, pore connectivity decreases, and particle migration becomes prominent, especially for particles smaller than 20 μm. These changes have significant impacts on remaining oil distribution and recovery rates. This study provides microscopic evidence for optimizing reservoir development strategies and holds important implications for enhancing recovery rates in mature oilfields.

Against the backdrop of global energy transition and strict environmental regulations, supercritical carbon dioxide (scCO₂) fracturing and oil displacement technologies have emerged as pivotal green approaches in shale gas exploitation, offering the dual advantages of zero water consumption and carbon sequestration. However, the inherent low viscosity of scCO₂ severely restricts its sand-carrying capacity, fracture propagation efficiency, and oil recovery rate, necessitating the urgent development of high-performance thickeners. The current research on scCO₂ thickeners faces a critical trade-off: traditional fluorinated polymers exhibit excellent philicity CO₂, but suffer from high costs and environmental hazards, while non-fluorinated systems often struggle to balance solubility and thickening performance. The development of new thickeners primarily involves two directions. On one hand, efforts focus on modifying non-fluorinated polymers, driven by environmental protection needs—traditional fluorinated thickeners may cause environmental pollution, and improving non-fluorinated polymers can maintain good thickening performance while reducing environmental impacts. On the other hand, there is a commitment to developing non-noble metal-catalyzed siloxane modification and synthesis processes, aiming to enhance the technical and economic feasibility of scCO₂ thickeners. Compared with noble metal catalysts like platinum, non-noble metal catalysts can reduce production costs, making the synthesis process more economically viable for large-scale industrial applications. These studies are crucial for promoting the practical application of scCO₂ technology in unconventional oil and gas development, including improving fracturing efficiency and oil displacement efficiency, and providing new technical support for the sustainable development of the energy industry. This study innovatively designed an amphiphilic modified amino silicone oil polymer (MA-co-MPEGA-AS) by combining maleic anhydride (MA), methoxy polyethylene glycol acrylate (MPEGA), and amino silicone oil (AS) through a molecular bridge strategy. The synthesis process involved three key steps: radical polymerization of MA and MPEGA, amidation with AS, and in situ network formation. Fourier transform infrared spectroscopy (FT-IR) confirmed the successful introduction of ether-based CO₂-philic groups. Rheological tests conducted under scCO₂ conditions demonstrated a 114-fold increase in viscosity for MA-co-MPEGA-AS. Mechanistic studies revealed that the ether oxygen atoms (Lewis base) in MPEGA formed dipole–quadrupole interactions with CO₂ (Lewis acid), enhancing solubility by 47%. Simultaneously, the self-assembly of siloxane chains into a three-dimensional network suppressed interlayer sliding in scCO₂ and maintained over 90% viscosity retention at 80 °C. This fluorine-free design eliminates the need for platinum-based catalysts and reduces production costs compared to fluorinated polymers. The hierarchical interactions (coordination bonds and hydrogen bonds) within the system provide a novel synthetic paradigm for scCO₂ thickeners. This research lays the foundation for green CO₂-based energy extraction technologies.

Excessive CO₂ emissions cause global warming, while CO₂ interaction with crude oil can enhance oil recovery (EOR). To capture and reuse CO₂, nano-SiO₂ was cationically modified to synthesize nanoparticles (SCR₂). The structure and performance of SCR₂ were characterized by FT-IR, DLS, and TEM, confirming its excellent CO₂ adsorption capacity and surface activity. Compared with unmodified nano-silica, SCR₂ increased CO₂ adsorption capacity by 254.3% and reduced the core surface contact angle from 112.1° to 24.5°. Core flooding experiments showed that in low-permeability reservoirs, SCR₂ achieved a plugging rate of 87.5%, an enhanced oil recovery of 24.8%, and an ultimate oil recovery of 74.8% (23.8% higher than unmodified nano-silica). Mechanistically, SCR₂ plugs gas channeling pathways via its inherent nanoparticle properties and adsorption of dissolved CO₂ in the aqueous phase while improving rock surface wettability, thereby enhancing sweep efficiency and total oil recovery during CO₂ flooding. This study provides a promising approach for EOR and CO₂ resource utilization in low-permeability reservoirs.

Clay mineral hydration dispersion and pressure transfer are the main factors leading to well wall instability during shale development. In this study, the surface of nano-SiO₂ was modified with silane coupling agent KH-550, polyethyleneimine PEI_30 000 and PEI₃₀₀, and three kinds of end-amidated nano-SiO₂ core–shell structural materials with different degrees of branching were successfully prepared. The results show that –NH₂ is truly present on the surface of three modified SiO₂ nanostructures. Additionally, the modified nanosilica nanoparticles show better dispersion in water and enhanced thermal stability compared with the unmodified sample. Linear swelling and drum recycling were used to investigate the inhibitory effect of sodium bentonite on water sensitivity, with BPEI@SiO₂ exhibiting the strongest inhibition against clay hydration expansion. At a 2.0 wt% concentration, it reduced the 16-hour expansion rate of sodium bentonite by 30.77%. Pressure transmission and microporous filtration membrane blocking demonstrated that the amine-terminated nano-SiO₂ exhibits a smaller particle size than the other samples, enabling effective blocking of pore channels within the rock core. The zeta potential and the clay-layer spacing test were used to thoroughly analyze the mechanism of action of the end-amidated nano-SiO₂. The results showed that all three types of modified end-amidated nano-SiO₂ exhibited effective chemical inhibition and physical sealing, as evidenced by a pronounced increase in the zeta potential of bentonite suspensions from −32.6 mV to −18.95 mV and a significant reduction in clay interlayer spacing after treatment with BPEI@SiO₂. The interactions between modified silica nanoparticles and shale showed different mechanisms of action for the modified nano-SiO₂ with different chain-length shells. KH550@SiO₂ neutralises the negative charge on the clay surface by protonating –NH₃ ⁺. BPEI@SiO₂ inserts into the bentonite crystal layer and reduces its crystal layer spacing to inhibit its hydration and swelling. In contrast, HPEI@SiO₂ features a larger and more distinctive hyperbranched polymer shell, which extends outward from the nanoparticle surface and enables simultaneous electrostatic adsorption onto the external surfaces of multiple bentonite grains.