Distinct element analysis for hydraulic fracturing in shale - Effect of brittleness on the fracture propagation

Hydraulic fracturing is one of the most important techniques for development of shale oil and gas resources. Brittleness index is considered to be an important factor for hydraulic fracturing. The effect of brittleness index on the fracture propagation was investigated by original flow-coupled DEM code. As the simulation results, followings were found. When rock models with small Young's modulus are used, average aperture of all microcracks is larger than those with large Young's modulus because it can deform easily. Therefore fracturing fluid infiltrates into the fracture tip immediately, and fluid pressure in fracture tip rises. As a result, stress intensity factor at fracture tip increases with the fracture length, and fracture propagates rapidly to one side of borehole. On the other hand, when rock models with large Young's modulus are used, only a small amount of fracturing fluid can infiltrate into the fracture tip due to small aperture of a fracture. Thus fluid pressure at fracture tip cannot increase easily, and the increments of stress intensity factor are lower at fracture tip. Thus, fracture propagates slowly to both side of borehole. Young's modulus that is a parameter of brittleness index significantly influences on the hydraulic fracturing propagation.