Transport Pattern and Placement Characteristics of Proppant in Different Rough Fractures

The transport and placement characteristics of proppant in rough fracture is of great significance for optimizing fracturing parameters and making proppant transport to the deep part of fracture for effective support. This paper scans the surface morphology of rock samples after fracturing, generates rough fracture based on the scanned data, and uses high-order interpolation function to generate fracture with different roughness, and establishes a numerical model of proppant transport in different roughness based on Euler-Euler two-phase flow model. The effects of different fracture roughness, fluid velocity, proppant size, proppant density and carrying fluid viscosity on the transport pattern and placement characteristics of proppant were compared and analyzed. The results show that: (1) The complex spatial structure of rough fracture hinders the transport of proppant and makes the placement of proppant in fracture uneven, with the characteristics of tortuous and variable; Compared with smooth fracture, the equilibrium height of proppant in rough fracture is higher, and more settlement at the front end of fracture is easy to cause sand plugging; (2) Higher fluid velocity, smaller density and size are conducive to the transport of proppant in rough fracture, which is not easy to cause sand plugging, and can make proppant be carried to the deep part of fracture for effective support (3) Increasing the viscosity of carrying fluid and reducing the size of proppant can significantly improve the sand carrying performance of fluid, and smaller proppant size can better pass through branch fracture. Compared with changing other process parameters, changing the viscosity of carrying fluid and proppant size has more significant effect. But in the field fracturing process, increasing the viscosity of carrying fluid is easier to achieve, so in the hydraulic fracturing process design, the viscosity of carrying fluid should be considered first, and 70% of dimensionless equilibrium height in rough fracture should be used as the critical point to evaluate sand carrying efficiency. Exceeding 70% is easy to cause sand plugging. Optimize fracturing parameters. It is recommended that fluid velocity should be greater than 0.2 m/s, proppant size should be less than 0.32 mm, proppant density should be less than 2600 kg/m(3), and carrying fluid viscosity should be greater than 2 mPa s in field fracturing construction. (4) Proppant is placed in main fracture first in multi-cluster rough branch fracture, and then carried into branch fracture after reaching a certain height. It shows symmetrical distribution in branch fracture. It is suggested that smaller proppant size should be selected first in field fracturing construction process to enter branch fracture for effective support. The research results provide theoretical basis for realizing efficient filling of proppant in the deep part of fracture and optimizing fracturing parameters.