American Oil and Gas Reporter - August 2019 - 107

SpecialReport: Hydraulic Fracturing Technology

Downhole Insights Power Frac Design
By Colter Cookson
For completion engineers to design
hydraulic fracturing jobs that have the
right stage spacing, pump rates and frac
fluid chemistries, they need to reach accurate conclusions about the downhole
environment. Only then will they be able
to place clusters in rock with similar
qualities to maximize cluster efficiency,
predict how far fractures will extend to
minimize interference between wells, and
identify the most effective chemistries
for maximizing proppant transport.
Fortunately, the industry is getting
better at assessing downhole conditions.
Today, service companies report completion engineers can create pseudo logs
from readily-available surface drilling
data, characterize fracture networks after
each stage without disrupting their operations, and send fast-moving cameras
down hole to measure perf erosion, an
indicator of proppant placement.
As modern completion software simplifies data collection and analysis, the
information operators gather about each
well is becoming easier to turn into better
fracs. Meanwhile, service companies say
electric frac fleets and advanced friction
reducers are allowing pressure pumpers
to deliver higher-quality completions at
a lower cost.
Surface drilling data is one way completion engineers can gain useful information, says Mohit Paryani, an engineering
team lead with FracGeo. "Detailed logs
would be better, but because acquiring
logs in the lateral is expensive, FracGeo
has developed models that transform surface drilling parameters, which we already
collect, into information about the reservoir. These models are based on corrected
mechanical specific energy (CMSE), or
the amount of energy the bit needs to
break the rock."
Mechanical specific energy models
have been used to estimate rock elasticity
for years, says Peter O'Conor, the company's vice president of sales and marketing.
"In the past, they worked well for relative
comparisons but lacked the accuracy to
estimate absolute values," he says. "One
of the biggest issues is the amount of
energy lost to friction between the bit and
the surface, which can cause surface parameters such as torque, rate of penetration
and weight on bit to be misleading unless

we correct for friction."
With new models that accurately evaluate torque and drag, O'Conor says those
corrections can be made quickly and
easily. He adds that surface drilling parameters now can be used to estimate
pore pressure, differential stress and natural
fractures in addition to rocks' static mechanical properties, thereby accounting
for all major frac gradient drivers.
"In some cases, the drilling parameters
can be even more accurate than log-based
information," O'Conor says. "For example,
Equinor worked with us to estimate pore
pressure across a multicounty asset in
the Eagle Ford play and compared the
results with direct measurements and traditional estimates based on rock compaction. Relating pore pressure to compaction works well for young, Gulf Coasttype rocks in conventional plays, but
CMSE is a better fit in tighter formations,
so the drilling-derived estimates were
more accurate."
Fast Simulations
To turn data on static rock properties,
pore pressure, differential stress and
natural fractures into the right decisions,
operators often use simulators to see how

fractures are likely to propagate and to
predict stimulated reservoir volume,
O'Conor notes.
"This data can be transferred to a
reservoir simulator to estimate production
and depletion," he comments. "Understanding depletion is vital for determining
the best lateral spacing to avoid frac hits
or other interference between wells."
FracGeo's fast reservoir simulator can
analyze a given stimulated reservoir volume's effect on production, reservoir depletion and child wells in only a few
minutes, O'Conor reports. "This is much
faster than a conventional numerical simulator, which could take several hours to
make the same calculations," he says.
"We are able to achieve that speed without
a meaningful loss in accuracy using a
simulation technique called the fast marching method, which solves the diffusivity
equations using one-dimensional approximations. This allows operators to test
more ideas."
O'Conor mentions that FracGeo is
working with a consortium of operators-
including majors such as Shell and Total,
as well as independents such as Anadarko
Petroleum, Jagged Peak Energy, DJR Energy, SRC Energy, Sundance Energy,

With new models, surface drilling parameters such as torque and weight on bit can be
turned into accurate pseudo logs of differential stress, pore pressure, natural fractures,
porosity and static geomechanical properties, FracGeo reports. In addition to guiding
geosteering during drilling, these pseudo logs can be combined with fast simulations
to help operators pinpoint the best completion designs.

AUGUST 2019 107
American Oil and Gas Reporter - August 2019

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