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In order to explore the law of proppant migration and placement under clean fracturing fluid, an Euler multiphase flow model was established through FLUENT numerical simulation software based on computational fluid dynamics(CFD). The model takes into account the rheological properties of fracturing fluid and the friction and collision of proppant particles. The influence of proppant size, density and sand ratio on the shape of the sand dike is studied by using the equilibrium height and equilibrium time as the characterization parameters. The results show that the clean fracturing fluid is easier to carry the proppant to the depth of the fracture than the conventional fracturing fluid, so that the proppant is evenly distributed in the fracture; proppant with large particle size and high density can easily settle in the fracture opening under the carrying of the clean fracturing fluid, while proppant with small particle size and low density can improve the sand carrying capacity of fracturing fluid and transport proppant into deep fracture. Increasing sand ratio in a certain range can improve the height and laying area of the sand dike, but excessive sand ratio has little effect on the shape of the proppant sand dike and is easy to cause sand blockage.

Clean fracturing fluid exhibits desirable characteristics, such as low residue, easy flowback, minimal reservoir damage, and favorable rheology, making it highly adaptable. However, challenges remain in terms of high cost, large consumption, and poor stability. Hence, this study focuses on incorporating SiO2 nanoparticles into clean fracturing fluid to develop a novel nano‐modified system. Experimental tests were conducted to analyze the impact of mass fractions of hexadecyltrimethylammonium chloride (CTAC), sodium salicylate (Nasal), and SiO2 nanoparticles on the viscosity of the solution. The results indicate a significant increase in viscosity with higher mass fractions of SiO2. A nano‐modified clean fracturing fluid composition of 1.5 wt% CTAC, 0.4 wt% Nasal, and 0.1 wt% SiO2 was selected as it meets the technical specifications for fracturing fluid while exhibiting excellent elastic modulus (2.279 Pa) and viscous modulus (0.818 Pa), thereby displaying superior viscoelastic properties. Furthermore, the system maintains a viscosity above 20 mPa.s under temperature (70°C) and shear stress (170 s−1), indicating robust temperature and shear resistance to meet the demands of downhole fracturing and proppant transport. Based on rheological experimental data, a Carreau rheological model was established for the nano‐modified clean fracturing fluid. Considering particle interaction, wall blockage, and fluid filtration, a settlement model was modified with a correction coefficient, leading to the construction of a mathematical model for correcting proppant particle settling in fractures. The error between measured settlement velocity and calculated values remained within 10%. Finally, the migration law of proppant is studied, and the settlement law of proppant in fracturing fluid and fracture is clarified. [ABSTRACT FROM AUTHOR]

N 2 injection into coal seams can effectively enhance the gas flow capacity in the late stage of pumping, thereby improving the recovery rate and recovery efficiency of low coalbed methane (CBM). To reveal the thermodynamic flow coupling relationship between the reservoir and the gas phase and its transportation mechanism in the process of thermal N 2 injection, a mathematical coupling model of N 2 injection that considers the deformation of the coal seam, fluid transportation, and temperature change was established. The influence of the seepage heat transfer effect of the coal seam under the effect of N 2 injection on the CH 4 extraction rate was investigated using this model. Results indicate that the action mechanism of N 2 injection in coal seams includes increasing seepage, promoting flow, and displacing gases. A higher initial coal seam temperature results in a smaller thermal expansion and deformation of the coal skeleton during thermal N 2 injection and less pronounced coal permeability increase. A larger initial coal seam permeability results in more favorable N 2 diffusion, which strengthens the flow-promoting effect on CH 4 . The effect of gas injection pressure on CH 4 recovery is greater than that of the gas injection temperature: High pressure promotes N 2 seepage, carries CH 4 flow, and increases the CH 4 diffusion effect, whereas higher temperature promotes the desorption of adsorbed gas in the coal seam and improves the recovery rate., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)