Abstract
The question of how slurries are transported and placed during hydraulic fracturing treatments was first broached by Kern et al. (Kern, Perkins et al., 1959), in 1959. In the early 90’s, Cleary and Fonseca (Cleary and Fonseca Jr., 1992) suggested that gravity acting on the slurry as a whole would cause the heavier slurry to fall through the fluid in the fracture and that this would dominate individual particle settling in determining the final distribution of proppant. This sparked a healthy debate concerning the nature of flow into a fracture and brought about a renewed interest in fracture fluid flow. A fracture is analogous to a Hele-Shaw flow cell. However, most experimental studies that deal with flow in fractures assume that the fracture is globally uniform with constant height and width. This is hardly the case in real fractures. Downhole cameras have revealed that fractures are anything but uniform. There are wide and narrow regions coupled with abrupt changes in uniformity. In addition, pressure analysis indicates that, in many cases, the height of the fracture changes during most of the treatment. These all serve to disturb not only bulk slurry flow but also the settling behavior of the particles that make up the slurry. While it is difficult to simulate the growth of a fracture experimentally, width non-uniformities can be simulated and their effect on slurry flow determined. A method that can be used to predict the behavior of the slurry in the presence of a non-uniformity will be presented. These techniques can be incorporated into computer models to improve predictive capabilities.
