Material Selection
Material Selection
The proppant selected for a fracturing treatment must be capable
of holding the fracture faces apart so that formation fluids can
flow through the fracture with a minimal loss of energy, and it
must be long lasting. From a practical standpoint, it should be
capable of being placed using pumping equipment and a fluid system
that are currently available. It should also be readily available,
safe to handle, and relatively inexpensive.
Sand is the least expensive proppant available. The
superior-performing Northern White Sand generally commands a
slightly higher price than the Texas Brown Sand. Intermediate
Strength Proppant (ISP) products generally cost about three to
eight times as much as sand, and sintered bauxite 10 to 20 times
more expensive than sand. Additionally, service companies usually
include a small surcharge for pumping larger and premium proppants
to defray the increased wear on their pumping equipment.
The fact that sand looses part of its permeability at higher
closure stresses does not automatically mean that we must select a
more expensive proppant above a certain closure stress limit. We
could always consider compensating for the loss in dimensioned
conductivity by designing for larger widths (i.e., larger areal
proppant concentration). The correct decision will involve a
detailed cost analysis of the available options. One possible
compromise is to use a less expensive proppant for the major part
of the treatment, and then "tail in" with high-quality proppant at
the end.
The fluid selection process involves careful consideration of
the fluids primary functions, which include fracture initiation,
fracture propagation, proppant transport, and post-treatment return
to the wellbore. The most important concern should be sufficient
proppant transport and leakoff control. The use of complex and
expensive fluid systems is not always justifiable. For instance,
while expensive additives might provide excellent leakoff control
in a homogeneous matrix, they would be much less effective in
formations where fluid loss is governed by a natural fracture
network.
