Fluid Flow in Vertical Fractures From a Point Source
- P.E. Clark (U. of Alabama) | Qinsheng Zhu (U. of Alabama)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- March 1995
- Document Type
- Journal Paper
- 209 - 215
- 1995. Society of Petroleum Engineers
- 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.3.2 Multiphase Flow, 5.3.3 Particle Transportation, 2.4.3 Sand/Solids Control, 4.3.4 Scale, 4.1.5 Processing Equipment
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Flow into a fracture from a point source recently has been the focus of attention in the petroleum industry. The suggestion has been made that, in this flow configuration, convection (gravity-driven flow) would dominate Stokes' -type settling for determining final proppant distribution. The theory is that when a dense fluid flows into a fracture filled with a less dense fluid from a point source, the density of the fluid will force it to the bottom of the fracture. This clearly happens when the two fluids have low viscosity. However, viscosity of both the fluid in the fracture and the displacing fluid and nonuniformities in the fracture influence displacement process significantly. Results presented in this study clearly show the effects of viscosity and fracture nonuniformity on the convective settling mechanism.
While this paper deals with the convection mechanism for proppant transport in a vertical fracture, a review the history of proppant transport and placement is appropriate to help understand the experimental modeling of fracture flow better. Kern et al. reported the first model study. Their model was small, and their study dealt primarily with equilibrium velocities (the velocity where the height of the settled bed ceases to change). The authors used no crosslinked fluids and presented only limited data on thickened fluids. This paper laid the groundwork for the concepts of bank buildup and equilibrium velocity, concepts that dominated early thinking on proppant transport.
Babcock et al. made the next contribution to laboratory fracture-flow modeling. Their model was longer than that used by Kern et al., and they used several concentrations of guar and different sizes and types of proppant, fracture widths, and flow rates for their study. Their results were reported in terms of equilibrium bed heights, settling velocities, and equilibrium velocities. Schols and Visser reported data from a model that was ˜ 10 ft long and 1 ft high. Their work focused on equilibrium velocity and bank buildup and resulted in a set of equations that could be used to predict bed height and length.
Most of the early work with fracture models involved determining equilibrium velocities and equilibrium bed heights for "bankbuilding" fluids. Models constructed after 1975 were used to study particle settling. Clark et al. constructed a 12-ft-long by 4-ft-high model. This model was used to determine settling velocities in guar and hydroxypropyl guar (HPG) solutions. This paper includes what appears to be the first report of particle clustering during settling after shutdown. Sievert et al. report further data from the use of Clark et al.'s model. They observed that pack-growth rate as a function of proppant concentration in non-Newtonian fluids was nonlinear and that doubling of the viscosity of non-Newtonian fracturing fluids would result in a several-fold decrease in particle-settling velocity.
|File Size||3 MB||Number of Pages||7|