Based on the issue of low efficiency of CO2 displacement and sequestration in different low-permeability reservoirs, the impact of different CO2 injection methods (continuous CO2 injection, water-alternating-gas (WAG), and Huff and Puff (HnP)) on the microscopic oil production and CO2 storage in low-permeable reservoirs are studied by conducting several experiments, aiming to select the optimal CO2 injection and storage strategy. Nuclear magnetic resonance (NMR) was employed to analyze the microscopic oil recovery and CO2 storage within different scales of pores of cores. The results indicate that CO2 miscible injection enhances mass transfer and reduces interfacial tension (IFT) between CO2 and crude oil, expands the CO2 sweep volume and oil washing efficiency in reservoir cores, and ultimately improves the oil recovery. CO2 miscible WAG (CO2-M-WAG) with a gas-water ratio of 1:1 and a single water or CO2 slug size of 0.1 pore volume (PV) of cores achieved the highest oil recovery and CO2 storage percentage after displacing the cores, followed by continuous CO2 miscible flooding (CO2-MF). In contrast, the use of a CO2 miscible Huff and Puff (CO2-M-HnP) resulted in relatively low oil recovery and CO2 storage for the cores. During the process of CO2-M-WAG, the mass transfer between CO2 and the oil phase is promoted, and the premature breakthrough at the core outlet end is also mitigated by stabilizing the CO2 displacement front. Otherwise, relative permeability hysteresis occurs during the CO2 WAG process, leading to some CO2 being isolated into clusters in certain small pores and throats, thereby enhancing CO2 storage. Therefore, to simultaneously Enhance Oil Recovery (EOR) and CO2 storage in low-permeable reservoirs where CO2 gas channeling is prone to occur prematurely, the optimal CO2 injection method may be the CO2-M-WAG with an optimized gas-water ratio.
Premature CO2 breakthrough in production wells during CO2 flooding is a significant factor that limits the enhanced oil recovery (EOR) effect in low-permeability reservoirs. To improve oil production efficiency, experiments on CO2 immiscible injection and in situ nuclear magnetic resonance (NMR) analysis were conducted to identify the dynamic patterns of oil production in different locations and various pore sizes in low-permeability cores under several CO2 displacement methods. The findings indicated that continuous CO2 immiscible flooding (CO2-IMF) primarily extracts oil from the larger pores of the cores. Increasing the displacement pressure reduces the pore radius limit for oil production, which can also lead to earlier CO2 breakthrough from larger pores or fractures. The CO2-water alternating injection (CO2 WAG) and the combination of CO2-IMF with CO2 Huff-and-Puff (HnP) effectively suppress earlier CO2 breakthrough in production wells. However, the combination of CO2-IMF and HnP shows a more significant improvement in oil production, particularly for oil trapped near the production wellbore and in smaller reservoir pores. When comparing the oil production effects of CO2-IMF at 18 MPa, the pore radius limit for oil production decreased from 0.06-0.17 to 0.04-0.14 mu m, resulting in an increase in oil recovery by 5-20% with the combination of CO2-IMF and HnP. The study results may guide the optimal scheme design of controlling CO2 premature breakthrough and recovering residual oil near the wellbore of low-permeability reservoirs.
Superhydrophilic surfaces have garnered significant research attention to their broad applications in drag reduction, antifouling, oil-water separation, and other related fields. However, the application of superhydrophilic surfaces has limitations that should not be overlooked. These include reduced surface durability and bonding due to water absorption and swelling, loss of performance in the event of cracks or fractures, and unstable coating performance in complex water environments. To address these issues, we have developed a highly durable, self-healing, superhydrophilic surface that retains its underwater super-oleophobic properties (underwater oil contact angle > 150 degrees) after undergoing 80 cycles of sandpaper friction and immersion in harsh aqueous environments (pH = 2, pH = 12 and man-made seawater). Not only is the coating self-healing in air, it also self-heals and regains wettability in harsh aqueous environments (pH = 2, pH = 12 and man-made seawater). In addition, the coating's excellent anti-fouling, drag-reduction and oil-water-separation properties pave the way for its widespread use in engineering applications.
A terahertz-band single-polarization (SP) hollow-core anti-resonant fiber (HC-ARF) based on asymmetric cladding structures is proposed. In the Y axis direction, the mixed nested structure based on circular and elliptical tubes is used to suppress the loss of the Y-polarized fundamental mode (YPFM). The X axis cladding structure is composed of an outer circular tube with gradient wall thickness and two inner circular tubes which can enhance the transmission loss of the X-polarized fundamental mode (XPFM). The numerical analysis results demonstrate that the losses of XPFM and YPFM are 1.05 dB/m and 3.1 & times; 10(-5) dB/m, respectively, at 1 THz. The ultra-high polarization loss ratio (PLR) of 33 727 is achieved. Meanwhile, the PLR can be maintained greater than 100 in the range of 0.96-1.04 THz and 1.115-1.125 THz. The excellent performance of the designed HC-ARF further expands its application potential in the terahertz-band.
On-demand adhesion superhydrophilic/underwater superoleophobic coatings can significantly simplify the functionalization and regeneration processes of equipment surfaces, while also offering significant economic benefits and environmental sustainability advantages. However, preparing superhydrophilic/underwater superoleophobic coatings that can simultaneously satisfy high adhesion and on-demand adhesion remains a critical challenge. In this study, an on-demand adhesion, self-healing superhydrophilic/underwater superoleophobic coating (EDPE) based on nonwoven fabric was designed and fabricated by integrating the temperature-responsive mechanism of tardigrades with the superhydrophilic properties of fish mucus through a multi-level biomimetic structure. The produced EDPE coating retained its structural integrity and underwater superoleophobicity after 160 friction cycles and immersion in complex water environments (pH=2, pH=12, and artificial seawater), achieving self-healing and the restoration of underwater superoleophobicity in complex water environments. The coating also exhibited excellent adhesion properties on various materials, as well as repeatable adhesion and retention of its underwater superoleophobic performance through temperature response, offering outstanding resistance to external forces and environmental changes. In addition, the coating demonstrated excellent antifouling, drag reduction, and antibacterial properties. Notably, this work proposed a simple and effective design strategy for on-demand adhesion and self-healing superhydrophilic coatings. The approach could enable scalable manufacturing processes, offering new insights for industrial applications requiring advanced surface engineering solutions.
