Numerical analysis of the material parameter effects on the initiation of hydraulic fracture in a near wellbore region

Hydraulic fracturing is recognized as a key method to enhance unconventional reservoirs, but it is also quite complicated and challenging due to so many affecting factors such as the formation material parameters, fluid behaviors and geological setting/conditions. However, in unconventional reservoirs, in the near wellbore region, the rock may consist of different materials, and the stress is redistributed during drilling and fracturing process, so the preferable hydraulic fracture path is hard to predict. This paper aims to study the effects of formation material parameters, including drilling effects, on the hydraulic fracturing process in unconventional reservoirs. First, hydraulic fracturing has been simulated in nine cases with different parameters specifically permeability, porosity, Young's modulus, and Poisson's ratio. Then hydraulic fracturing has been studied by a heterogeneous model with multiple zones and layers, and complex stress condition. It is found that under a constant hydraulic pressure boundary, when the values of permeability, porosity, Young's modulus, and Poisson's ratio are higher, hydraulic fracturing initiates earlier; with a heterogeneous distribution of materials, stress concentration is formed between different materials, and the tensile stress concentrated areas become the preferable paths of hydraulic fracturing. (C) 2015 Elsevier B.V. All rights reserved.