Polymer-dominant drag reduction in turbulent channel flow over a superhydrophobic surface

The economic development of tight carbonate reservoirs requires hydraulic or acid fracturing stimulation. Acid fracturing better activates natural fractures, resulting in increased stimulated reservoir volume and improving oil and gas flowability. In order to solve the problem of excessive acid-rock reaction due to high temperature, this paper screened four kinds of solid forms of acid with the maximum quantity of acid and reaction rate as the index and formed a high temperature-resistant mixed solid acid system with solid organic acid as the main part and inorganic solid acid as the auxiliary part. The maximum quantity of acid produced and effective acid concentration of the system were greater than 50%, and no residue was precipitated after the complete reaction. Dynamic acid-rock rate tests were performed on different types of retarded acid at 140 °C. The test results show that the solid acid dissolves to form a low-viscosity acid solution, and the reaction rate is one order of magnitude lower than that of gelled and cross-linked acids at the same hydrogen ion concentration, and it is little affected by temperature. Moreover, the paper compares the treatment effect of micro-proppants and solid acids on micro-fractures. The results show that the core permeability improvement multiples up to 900 times under low dissolution of solid acid and the formation of oil and gas flow channels with the same scale as micro-proppants. The experimental results demonstrated the ability of solid delayed acid to transport the fracture leading edge at high temperatures and effectively activate micro-fractures.

Improving oil and gas flowability in tight carbonates with a novel solid delayed acid

Wang,

Zhou,

Yang

et al. 2024

Promote or inhibit turbulence drag reduction behavior of surfactant solutions with different micelle structures by certain nanoparticle addition

Li,

Wang,

Zhang

et al. 2024

The micelle structure of surfactant is easy to be destroyed in the flow process resulting in a decrease in its drag reduction (DR) efficiency; therefore, how to strengthen the stability of the micelle structure during the flow process and thus improve the drag reduction efficiency deserves intensive research. In this work, by comparing a variety of nanoparticles, hydrophobic silica nanoparticles were selected as the best additive to enhance the turbulence drag reduction efficiency of surfactant solution with spherical micelle structure. The experimental results also demonstrated that the hydrophobic silica nanoparticles had a reinforcing effect on anionic, cationic, nonionic, and zwitterionic surfactant solutions with the same concentration (dominated by spherical micelles), and the optimal nanoparticle addition concentration and maximum drag reduction rate were obtained. Meanwhile, the effect of silica nanoparticles on the turbulence drag reduction efficiency of surfactant solutions with different micelle structures was evaluated by inducing the surfactant micelle structure change. It was shown that the hydrophobic silica nanoparticles had a strengthening effect on the turbulence drag reduction performance of surfactant solutions with spherical micelle structure, while they had an inhibiting effect on the turbulence drag reduction performance of surfactant solutions with worm-like micelle structure. The change in solution viscoelasticity indicated that the decrease in viscoelasticity was the main reason for the decrease in drag reduction efficiency of surfactant solution with worm-like micelle structure when silica nanoparticles were added. A mechanism for the interaction of hydrophilic/hydrophobic silica nanoparticles with spherical micelles and wormlike micelle structures was finally discussed and proposed.

Influence of a dynamic gas film on underwater drag reduction

Liang,

Wang,

Wang

et al. 2024

The gas film at the liquid–solid interface, induced by hydrophobic microstructure, can achieve a high-efficiency underwater drag reduction. However, previous studies have rarely considered the impact of changes in gas structure morphology on drag performance, especially under turbulent conditions. We conducted numerical simulations to examine the dynamic process of gas on a hydrophobic spanwise grooved surface under turbulent conditions. Our findings indicate that the morphology of the gas phase structure at the liquid–solid interface undergoes continuous alterations due to fluid action, resulting in a dynamic state of drag performance. In addition, the gas morphology that completely covers the groove surface will reduce the turbulent kinetic energy on the groove surface, resulting in a better drag reduction effect. In the flow velocity range of 10–20 m/s, the drag reduction effect of the superhydrophobic grooved surface increases with the flow velocity. Finally, we conducted experiments to validate the effectiveness of this result. A mechanism for underwater drag reduction was proposed based on these simulation results. This study offers a novel perspective on the phenomenon of underwater gas drag reduction, which could significantly influence its practical applications, especially under real working conditions.