Abstract:

The studies on the characteristics of hydraulic fracturing under different conditions have an important meaning to the
effective shale gas exploration. As rocks are composed of grains and pores at micro scale, the discrete element method is introduced to
simulate hydraulic fracturing processes. The rules of energy calculation and energy conversion in the models are proposed and a 3D
discrete element model is built. Furthermore, 3D discrete element numerical simulation software“MatDEM3D”is developed. The
variations of strata stress and hydraulic speed are simulated by varying the model vertical strain and the particle diameters,
respectively. The simulation results indicate: (1) the number and direction of hydraulic fractures are influenced by the anisotropic
properties of rocks, stress state, and hydraulic speed. (2) Fractures are generated when the compressive wave passes. When hydraulic
pressure increases at a high rate, the number of induced fractures is much greater. Furthermore, the percentage of effective energy

(fracturing energy) is also greater, and as a result, the efficiency of hydraulic fracturing is higher. (3) When the vertical strain is zero,
50% of the fractures are vertical. When the vertical strain is -1×10-4, the fractures tend to develop along the direction of the maximum
compressive stress, and the percentages of vertical fractures are greater. The numerical simulation and energy analysis provide a new
method for researching the hydraulic fracturing processes of rocks.

Key words: hydraulic fracturing, discrete element method, MatDEM, energy