Highly deviated or horizontal wells completed in tight formations are frequently aligned with the minimum principal formation stress and completed with evenly spaced, transverse hydraulic fractures. When a transverse hydraulic fracture is created, unexpectedly high fracture-propagation pressures are often enocuntered. The hydraulic fracture-growth simulators currently available cannot explain these high treating pressures. There-fore, the pressures have been attributed to complex fracture geometries. Another likely cause of unexpectedly high fracture-treating pressures is the fracturing-fluid flow regime under which transverse hydraulic fractures are created. In transverse fractures, fluid flows radially outward from a "point source" (the wellbore). Flow is not linear, as implicitly assumed and hard-coded in many of today's hydraulic-fracturing models or simulators. Where radial flow exists under a constant injection rate, fluid velocities are much greater near the wellbore than out in the fracture. This condition causes high near-wellbore pressure gradients, which result in relatively high fracturing-fluid pressures in and near the wellbore, compared with pressures out in the hydraulic fracture. This pressure-profile effect on fracture-propagation pressure and created fracture dimensions is demonstrated with analytical calculations. The pressure profiles analyzed include a constant pressure throughout the fracture (the equilibrium base case) and a parabolic pressure decay along the length of the fracture (the most severe case considered). The calculations show that, for severe hydraulic-fracture pressure profiles, the fracture-propagation pressure in the wellbore can be more than 12 times greater than the propagation pressure required for constant pressure throughout the fracture. The more severe the pressure drop in the near-wellbore region, the wider and shorter the hydraulic fracture will be. Results from these calculations suggest procedural changes for minimizing the effects of adverse pressure profiles. They also demonstrate that current hydraulic-fracturing models and simulators must be modified to account for the pressure profiles expected under radial-flow conditions.
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