American Oil and Gas Reporter - January 2017 - 106

Tech Trends

Packers Influence STACK Production
By Scott Van Sickle, Chad Senters, and D.J. Snyder
OKLAHOMA CITY-As part of the
continual optimization process in resource
plays, operators continue to evaluate completion techniques and best practices to
improve efficiencies, reduce costs, and
optimize performance practices. In Oklahoma's STACK play, completion performance was evaluated by examining
completion practices and diagnostics data.
A macroscopic production analysis was
completed to complement the diagnostic
results.
The objective of the project was to
evaluate completions, and compare technologies and optimization methods implemented in the STACK play. Each well
was categorized to maximize the number
of unchanged variables, and observations
were made on the overall stimulation
coverage of each treatment interval evaluated, isolation between stages completed,
and production trends. The results provide
valuable insights for both operators and
service companies.
As one of the most prolific plays in
the United States, the STACK includes
multiple oil-rich reservoirs that are stacked
vertically. Chaparral Energy's lease position, for example, includes more than
110,000 net surface acres with stackedpay potential in the Oswego, Meramec,
Osage, Woodford and Hunton formations.
The stacked nature of the plays allows
for effective and cost-efficient recovery
from multiple formations using horizontal
pad drilling.
The carbonate formations are characterized by an extensive network of natural
fractures that is conducive to uncemented
completion systems, but contributes to
negatively pressured reservoirs. This requires operators to stimulate wells at
high pump rates that can exceed 100
barrels a minute, at times.
The prevalence of natural fractures
encountered in the STACK often is linked
with additional production and makes it
difficult to obtain consistent annular isolation in a wellbore with cement. Early
wells in the play's development mostly

used cemented casing and plug-and-perf
completions. Figure 1 shows a log section
from one of these wells. It is clear that
stimulations from previous and subsequent
stages grew together during the plugand-perf treatment.
Because of the challenges of cementing
in a highly naturally fractured zone,
Chaparral Energy shifted to using uncemented, multistage completion systems.
It also initiated a well diagnostics program
to determine the effectiveness of these
systems in STACK horizontals and to
continue improving operations after implementation.
Uncemented Systems
In uncemented completion systems,
isolation packers are run into the wellbore
with fracturing ports as part of the liner.
The lateral section is left uncemented
and the packers are set to provide annular
isolation between stages, allow fluid/proppant pumping, and limit pressure accumulation to a single stage at a time. The
well then is stimulated using size-specific
actuation balls to open fracture ports
stage by stage in one continuous pumping
operation.
An alternative to ball-drop technology
for isolating internal stages is pumping
down bridge plugs and perforation guns

to provide communication to the annulus.
Traditional, hydraulically set mechanical packers (HSMPs) are characterized
by a dynamic setting mechanism that
uses surface pumping pressure to continuously increase the sealing force (packoff) on elastomer element(s) to enhance
sealing. HSMPs typically have been made
with a single element (SHM) or single
piston. More recently, however, hydromechanical packers have been redesigned
to include dual elements, with the functionality of hydraulically setting on a
single packer body.
Dual-element (DHM) packers use separate rubber elements, which are compressed by means of two opposing pistons
in the center of the packer elements to
create two independent sealing points
against the wellbore. The two elements
together act as one long seal, with the
advantage of redundancy. DHM packers
are set by increasing liner pressure, which
causes the setting pistons to move in opposite directions to set both elements.
Rather than being set by hydraulic
force, swellable element packers (SEPs)
expand in the presence of either water or
oil. SEPs typically are bounded by antiextrusion rings to ensure a tight seal
against the wellbore. The fluid is absorbed

FIGURE 1

106 THE AMERICAN OIL & GAS REPORTER

Tracer Log of Cemented STACK Well

American Oil and Gas Reporter - January 2017

Table of Contents for the Digital Edition of American Oil and Gas Reporter - January 2017