American Oil and Gas Reporter - January 2017 - 111

to identify any trends or anomalies that
have to be taken into account prior to
evaluating individual portions of a treatment.
Tracers can show up along the wellbore
or within certain stages during the cleanout of a lateral. Special consideration
should be given to wells in which the
formation took an excess amount of fluid
during clean-out. In many of the logs,
two passes were made with the tool string
to verify movement of proppant tracer
during the logging run and to confirm
tracer inside pipe. Sometimes, beads of
proppant tracer appear at a casing collar
or other hardware within the well, and
may not be mobile during the multiple
passes of the tool string.
More than 50 wells completed in Oklahoma's STACK play were analyzed using radioactive proppant tracer to identify
stages that were isolated during stimulation
treatment in uncemented wells. Many of
the wells contained internal isolation failures on greater than 50 percent of the
stages completed. Those wells were excluded so that the analysis could focus
on annular isolation between each stage,
leaving 29 wells, all of which were completed in 2016. Two wells used DHM
packers, nine used SHM systems, 11
used water-swellable packers, and seven
used oil-swellable packers.

Pump rates and minimal acting differential pressures were fairly consistent
across the wells, with pump rates ranging
from 78 to 100 bbl/minute and minimal
acting differential pressures were between
3,217 and 3,557 psi. Table 1 summarizes
the effectiveness of the various annular
isolation methods.
Although only two DHM wells were
available for this study, the DHM packer
had the highest number of isolated stages
at 78 percent. Water-swellable packers
had 46 percent isolation, while oilswellable and SHM packers both had
only 18 percent (the wells with SHM
packers had some internal isolation failures, which resulted in difficulty distinguishing between internal and external
failures).
In addition, the study examined estimated ultimate recoveries of barrels of
oil equivalent per lateral foot for 92
STACK wells completed by different
OHMS systems from multiple providers.
The best results were for a supplier that
ran DHM packers exclusively, while the
others used a mixture of single-element
and swellable packers. This correlation
indicates a relationship between isolation
effectiveness and productivity, with higher
isolation rates between stages leading to
higher production.
The diagnostic results of the STACK

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TABLE 1
Stage Isolation Effectiveness in the STACK Study
Isolation Type
Oil swellable
Water swellable
Dual hydromechanical
Single-element hydromechanical

Average Stages Isolated (%)
18%
46%
78%
18%

Number of Wells
6
11
2
10

FIGURE 4
Tracer Results in Cemented Plug-and-Perf Well where Plug Failed to
Provide Internal Stage Isolation

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American Oil and Gas Reporter - January 2017

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