American Oil and Gas Reporter - February 2018 - 23

Designed Screen-Outs
Offer Operators A Tool For
More Productive Wells
Recently, I came across an article in the Hydraulic Fracturing
Journal that highlighted why, in certain cases, a screen-out is not
necessarily a bad thing. The article, by BP's Prue Smith, explains
that during conventional hydraulic fracturing operations, the term
"screen-out" can carry a very negative connotation associated
with additional cost, complexity and time. However, during "frac
pack" operations, two screen-out events not only are planned for,
but constitute integral parts of a successful outcome. A tip screenout (TSO) is designed to increase the average fracture conductivity,
and a wellbore screen-out during the packing phase of operations
is designed to ensure the pack's quality.
The frac pack technique is applied widely in high permeability
reservoirs to eliminate sand production, penetrate past formation
damage and maximize the well's sand-free productivity. In a
highly permeable well, the required fracture conductivity (kfwf)
is the primary deciding factor in frac design and a shorter
fracture with higher conductivity tends to be more desirable
than the type of long frac that typically is designed for tighter
reservoirs. In order to maximize fracture conductivity, a frac
pack is designed to include a TSO. This phenomenon is observed
on the Nolte-Smith plot through a slope of one (or greater).
This event creates a wide propped fracture with a maximized
fracture conductivity.
Toward the end of the pumping operation, a wellbore screenout also is planned in order to efficiently pack the casing/screen
annulus. The wellbore screen-out is observed when surface
tubing pressure spikes as the annulus is packed. Both screen-out
timings are planned during the frac pack design phase, although
in execution one or both of the screen-outs may not occur
because of treatment/formation variance. When this occurs, an
operator will have appropriate contingency plans to adjust/influence
behavior during the pumping operations (such as reducing pump
rate, extending the proppant-laden fluid or reducing the crosslink). These adjustments can have unintended consequences,
such as severely impacting fracture conductivity (and distribution)
and thereby ultimately hurting the well's production.
Frac packing became widely used in the industry thanks to
production increases that resulted directly from a design that
maximized fracture conductivity. Conductivity is the product of
frac width and permeability (k w) and is the paramount variable
in frac packing, as it allows packing a high concentration of
proppant throughout the fracture and increases overall production.
As opposed to traditional hard-rock fracturing in low-to-moderate
permeability environments, which entails efforts to open very
long fractures to create a long conductive highway, frac packing
designs for short, wide fractures to achieve the paramount goal
of conductivity.
Frac packing became very popular in the 1980s as completions
in the deepwater Gulf of Mexico increased. The TSO method
originally was performed in the North Sea, where it developed
high conductivity fractures in a high permeability environment.
During the treatment, the low concentration, proppant-laden
slurry rapidly flows to the tip of the fracture and halts the

"Frac packing became widely used in the
industry thanks to production increases that
resulted directly from a design that maximized
fracture conductivity.

fracture propagation, creating the TSO. Once the tip screens
out, proppant concentration increases as pumping continues
and the fracture balloons, increasing aperture, conductivity and
net pressure. The TSO method helps create the 'frac' part of the
frac pack.
After achieving TSO and shortly the end of pumping commences, a pack around the screen annulus is designed for at the
wellbore. In order to create an annular pack, a wellbore screenout is designed at the end of the job. The wellbore screen-out
creates the 'pack' part of the frac pack, and is apparent as a
surface tubing pressure spike. The frac pack method has proven
itself through low skin values and production increases, and
therefore has been adopted widely across the industry for all
frac pack designs.
Smith's article concludes that, as long as the pump rate
exceeds the fluid loss rate, then the fracture should remain open
and increase in width and conductivity. If rate reduction is
chosen to try and induce TSO, then the pump rate must outpace
fluid loss in order to prevent an unplanned wellbore screen-out.
TSO possibly may be induced by extending the proppant-laden
slurry. Circulating in the annular pack using a step-down
schedule versus wellbore screen-out at maximum rate demonstrates
very little difference in results. Maximum rate wellbore screenout may compromise downhole equipment, and therefore it
may be better to circulate in the annular pack.
r

JEREMY VISCOMI is vice pres-

ident of global marketing for
Premier Oilfield Group in Houston and Mid-Continent regional
lead for the Petroleum Technology Transfer Council. For
almost 20 years, he has played
an integral role in many oil
and gas industry technical conferences and special events.
FEBRUARY 2018 23

American Oil and Gas Reporter - February 2018

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