American Oil and Gas Reporter - March 2022 - 63

SpecialReport: Resource Science
Of course, Newton's law of gravitation
applies in laterals, too, where it has a
greater influence on proppant behavior.
Early on, most proppant stayed in suspension
because completions used thick
fluids, Baumgartner recalls.
" Even after we moved to slickwater
fracs, engineers who looked at velocity
and turbulence would predict sand would
stay almost uniformly mixed with the
water from the heel-most perforation to
the end of the toe, " Baumgartner acknowledges.
" However, physical tests
and more realistic models show that
gravity causes sand to sink. "
Gravity's role became apparent while
GEODynamics was trying to figure out
why an operator's wells were not performing
as expected, recounts Phil Snider,
GEODynamics' senior engineering completion
adviser. " The rate and pressure
data from the completion suggested the
operator had done a fantastic job of injecting
fluid into the wells' clusters, but
when they ran production logs, they found
that only half the clusters were producing, "
he says. " Since we knew the operator
was putting fluid into the clusters, we
thought the uneven performance stemmed
from issues with proppant transport. "
To understand how proppant moves
down hole, a handshake-based consortium
was formed with several operators and
service companies to conduct tests. This
group invested about $5 million in surface
tests and downhole studies. " We thought
about trying to scale up experiments, but
given how much pressure is involved in
fracturing, it would have been difficult to
get accurate results in a small plexiglass
pipe, " Baumgartner says. " Instead, we
built a full-scale model by perforating
200 feet of 51
⁄2-inch casing at surface,
then capturing the fluid and sand coming
out of each cluster in tanks. "
After each test, a technician would
decant the water from the tanks and measure
how much sand remained. In the first
test, Baumgartner reports, the toe side
cluster had three times as much proppant
as the heel side cluster.
" The full-scale test drove home how
much gravity, fluid velocity and particle
size affect proppant distribution, " he reflects.
" As proppant flies past the heel side cluster,
it remains distributed evenly throughout
the fluid but is moving so quickly that
only the proppant very near the actual
perforation has a chance to exit the wellbore.
But as the fluid passes each perforation,
velocity decreases and sand settles out,
and the area surrounding the perforation
where proppant can exit increases. "
Improving Proppant Distribution
To figure out how to distribute proppant
more evenly, the consortium conducted
full-scale tests to evaluate several completion
scenarios, Snider shares. He says
these tests validated a model that uses
physics to predict how much proppant
each perforation will receive, given different
completion strategies.
" By applying this model, we think we
can help operators improve well productivity
10%-15%, " he estimates. " We do
not yet have the data to verify that, but
early tests show that recommendations
based on the model can reduce screenouts
and other issues. "
The model considers several factors,
including the casing's size and weight, the
perforating gun's orientation, the cluster
spacing, the number of perforations in
each cluster, total stage length, the pump
schedule and proppant size, Snider describes.
He says GEODynamics will run the model
for free for operators who use or are evaluating
its products, which include perforating
guns and charges. " Across the board, we
are seeing a strong match between the
model's predictions and the results operators
get in the field, " he reports.
Based on the model, Snider and Baumgartner
currently recommend orienting
perforating guns at three o'clock and
nine o'clock. They acknowledge that conventional
wisdom suggests pointing the
guns straight up or down to minimize
rock stresses that can inhibit fracture
growth. However, the model suggests
this approach leads to wide variations in
proppant distribution.
By pairing full-scale hydraulic fracturing
simulations at surface with downhole
studies, a coalition of operators and
service companies has shown how
much gravity, fluid velocity and particle
size influence variations in proppant distribution
across clusters. GEODynamics
says these experiments have validated a
physics-based model for predicting
proppant distribution that can help operators
increase production and reduce
screen-outs.
" If the guns are pointing up, the heelside
clusters tend to be undertreated because
the proppant velocity is too high
for the proportionate share to exit, " Baumgartner
clarifies. " As velocities slow, the
proppant concentration on the low side
of the pipe increases. The middle clusters
get the right amount, but by the toe, there
is so little fluid and velocity left and so
much proppant remaining that we see
extreme overtreatment. In fact, the proppant
concentration can be two or three
times as high at the toe as it is at the heel.
" If we instead point the guns down,
the pattern reverses, " he contrasts. " The
earlier clusters get overtreated because
gravity helps sand fall toward them, but
by the toe clusters, the sand has been depleted
and there is no longer enough to
hit the target concentration. "
The model indicates that alternating
between shooting up and shooting down
will level the swings in proppant distribution.
" However, the distribution is even
flatter with the guns at three o'clock and
nine o'clock, " Baumgartner reports. " The
well still will be slightly undertreated on
the heel side and overtreated on the toe
side, but to a lesser degree. In general,
MARCH 2022 63
American Oil and Gas Reporter - March 2022

Table of Contents for the Digital Edition of American Oil and Gas Reporter - March 2022
