Challenges in hydraulic fracturing from perforated boreholes in unconventional reservoirs

Abstract

In recent years, with the evolution of unconventional reservoirs, hydraulic fracturing has been applied to tight sandstone and shale formations to improve the hydrocarbon production. The application of hydraulic fracturing in cased boreholes is always associated with many difficulties because the fracture has to be initiated from the perforations. There have been many cases of improper fracture initiation in tight formations, which have then resulted in premature screen out, and have not improved reservoir production. In this study, initiation of hydraulic fracturing from a perforated tunnel was studied numerically using a finite element method. The numerical model was generated to represent a laboratory experimental test, which has been carried out on tight concrete cubic samples. A perforated wellbore in a linearly elastic tight formation was modelled using Abaqus software through three-dimensional numerical analysis. Two different perforation orientations were considered to analyse the fracture initiation pressure (FIP) and the location and initial direction of the crack. Different far field stresses were considered to study the effect of in-situ stresses and perforation directions on the fracture initiation mechanism. The results were then compared to laboratory and analytical outcomes, and good agreement was observed. The results provide a better understanding on how the stress regime, stress anisotropy, and perforation orientation could affect the pressure and geometry of fracture initiation in tight formations. Based on the outcomes of this study, better strategies can be decided for perforating a cased wellbore in a tight formation so that lower FIP is experienced and a better near wellbore fracture is created.