A laboratory study of the effects of stress regimes on hydraulic fracturing

Hydraulic fracturing is one of the most important stimulation methods for oil and gas reservoirs to increase fluid flow from low permeability reservoirs to wellbores. Various factors, such as in-situ stresses, joints and natural fractures of the formation, fluid rheology, mechanical properties of the formation, injection fluid flow rate and perforation operation, effect on the pressure and hydraulic fracture geometry. In this research, for the experimental investigation of the hydraulic fracturing, considering the reservoir condition, a three-axial machine with the ability to apply the main stresses was designed and built. Then, 32 concrete cubic samples with 10 × 10 × 10 cm dimensions were constructed and cured in the laboratory and the effect of the in-situ stress field and stress regime on the geometry and breakdown pressure, the pressure-time diagram, the pattern of crack propagation and finally the cross fractures in both vertical and horizontal wellbores were investigated. The results showed that increasing the maximum horizontal stress in the vertical wellbore leads to increased breakdown pressure and increasing deviatoric stress in the horizontal wellbore reduces the breakdown pressure.