Title: Convection/Encapsulation in Hydraulic
Fracturing
Author(s): S.N. Shah, The University
of Oklahoma and M. Asadi, Stim-Lab
Presentation: 1998 Rocky Mountain Regional/
Low-Permeability Reservoirs Symposium and Exhibition
Location: Denver, Colorado USA
Date: April 5-8, 1998
Abstract: New information is presented on the phenomena
of proppant convection and encapsulation in the hydraulic
fracturing treatments. To fully comprehend this
phenomenon, a unique parallel plate flow cell is used which
mimics field conditions and is integrated with a fiber
optic vision system. The vision system is used to enable the
visualization of proppant convection/encapsulation within the
fracture. The experimental study involves pulse injection of
both 6 and 10 ppg 20/40 mesh sand slurry of 35lb/Mgal borate-
crosslinked guar into various fluid media under static condition.
Data analysis shows that proppant convection/encapsulation is a
density/viscosity related mechanism. It is indicated that
encapsulation (downward motion of proppant) dominates particle
settling in a low viscous medium such as water or linear gel.
This phenomena, however, diminishes as viscosity of the lower
medium increases. In other words, particle settling within the
slurry cluster dominates proppant encapsulation and hence convection.
Therefore, it is ascertained that there exists an optium viscosity
value for a given range of density where the influence of density to
form encapsulation and convection is inhibited. According to this
study, a medium viscosity of 40,000 cp is suffice to sustain a
10ppg 20/40 mesh sand 35lb/Mgal borate-crosslinked slurry and to
prevent development of proppant encapsulation/convection. In
addition, to better understand the behavior of convection/encapsulation
in hydraulic fracturing, the effect of fracture gap width and
polymer concentration on the encapsulation/convection development
is investigated and presented.