ИСТИНА

The simulation of hydraulic fractures is an important research content that can guide the engineering practice to achieve the purpose of increasing production. Coal has approximately orthogonal face cleats and butt cleats resulting in the discontinuous performance. Discrete element method (DEM) has obvious advantages in studying mechanical properties of discontinuous materials, so based on the distribution characteristic of cleats in coal, the research on the propagation of hydraulic fractures is carried out via DEM. The simulated results show that: hydraulic fractures mainly propagate along the cleats towards the maximum principal stress. The fracture network can be formed due to the intersection of face cleats and butt cleats that can propagate at certain pressure. The general variation trends of 3DEC numerical simulated results are consistent with physical experimental results at the same condition. With the increase of injection rate and fracturing fluid viscosity, the maximum aperture of hydraulic fracture increases, while the length of principal hydraulic fracture shortens. Therefore, to achieve the purpose of forming hydraulic fracture network in coal seams with cleats, low viscosity fracturing fluid and low injection rate need be applied to the fracturing technology. As the cleat density increases, the number of branched fractures increases, but the length of principal hydraulic fracture becomes short.