Pressure Variations Inside the Hydraulic Fracture and Their Impact on Fracture Propagation, Conductivity, and Screenout

Abstract

Summary Field measurements of fluid pressure inside hydraulic fractures have shown rapid pressure declines along the fracture length. The consequence of this pressure profile is rapidly tapering fracture width. This means that a disproportionate volume of fluid and proppant injected inside hydraulic fractures remains near the wellbore, thus creating excessive near-wellbore and substantially less far-field fracture conductivity. This explains why history matching of oil well production figures yields much lower effective fracture lengths than when the same exercise is performed for gas wells, as oil wells require higher fracture flow capacity because of their higher permeability. The rapid tapering of the fracture width also restricts the movement of the proppant inside the fracture, causing its accumulation near the wellbore. As the treatment progresses, and if sufficient proppant volume has been injected inside the fracture, the near-wellbore segment of the fracture can begin to fill with proppant, thus reducing the open width available for further movement of the fluid. Essentially, accumulation of proppant near the wellbore reduces the fracture width available for fluid flow, which then results in higher frictional pressure losses inside the fracture, further skewing the pressure distribution and eventually leading to screenout.