Pressure Variation Inside the Hydraulic Fracture and Its Impact on Fracture Propagation, Conductivity, and Screenouts
Field measurement of fluid pressure inside hydraulic fractures shows rapid pressure decline along the fracture length. Actual field measurements show the rate of this pressure decline depends on fluid injection rate. The consequence of this pressure profile is a large degree of shear fracturing and branching near the wellbore and a 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 conductivities. This may explain why production history matching of oil wells yields much shorter effective fracture lengths than production history matching of gas wells, as oil wells, because of their higher permeabilities, require higher fracture flow capacities.
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, increasing the frictional pressure losses inside the fracture, further skewing the pressure distribution, and eventually causing a screenout. This fracturing phenomenon will be examined in detail in this presentation, as will its implications on hydraulic fracture design.