Axial Fracture Initiation During Diagnostic Fracture Injection Tests and Its Impact on Interpretations

Diagnostic fracture injection tests (DFITs) have been performed extensively in unconventional reservoirs to derive reservoir properties such as pressure, permeability, and closure stress. Since most horizontal wells in unconventional reservoirs are drilled in the direction of the minimum horizontal stress, prevailing studies typically presume that hydraulic fractures are oriented transverse to the wellbore direction. However, the near-wellbore stress concentration and perforation frictions may favor the initiation of fractures along the wellbore, which is perpendicular to the maximum horizontal stress. The possibility for the initiation of an axial fracture increases, if the injection rate is high enough or having low differential stress. In this study, we investigate the effect of initiation of the axial fractures on a DFIT test and its interpretation, using a fully coupled geomechanics and fluid flow model. First, we provide a model for the initiation and closure of axial fractures and transverse fractures during DFITs by coupling geomechanics with fluid flow. Then, using numerical simulations, we demonstrate that estimated closure stress can be misleading in the presence of an axial fracture. Finally, we discuss a potential method to determine the maximum horizontal stress under such circumstances.