American Oil and Gas Reporter - December 2017 - 58

zones during the first well treatment was
in the center of the log (the yellow zone,
representing the Upper Woodford section
with higher clay volumes and significant
variability). This was concerning because
of the issues experienced previously. Second,
while experience indicated that the interval
with poor productivity (orange, associated
with the black shale) typically would not
cause a significant issue during stimulation,
there was concern about the long-term
productivity because of the higher clay
volume in the near-wellbore region.
With these indices generated, the software then created the automated stage and
perforation placement and compared it
with the standard geometric placement of
200-foot stages with three perforation clusters a stage and 50 feet between clusters.
Figure 3B shows the sidetrack well's engineered stage and perforation design compared with the geometric design. Perforation
clusters were designed to minimize stress
contrast and rock type within a stage while
avoiding highly fractured areas.
The software also computed stress
differentials for each stage as calculations

of the differences between perforation
clusters in the highest and the lowest
stresses. This was performed for both
the engineered completion and the geometric design to enable comparisons. Additionally, the completions engineer could
use these data during treatment to determine which zones might experience stimulation issues. The engineered completion
for the sidetrack well had significantly
reduced stress differentials in comparison
with the geometric design. However,
stages 10-12 in the challenging zone still
showed high stress differentials.
Stage 11 in the geometric design was
almost an order of magnitude higher in
stress because perforation clusters were in
two significantly different rock types.
During stimulation, it is much more likely
that only one perforation cluster will fracture
and take all the fluid and proppant, leaving
the other clusters understimulated and causing a dramatic reduction in total SRV.
Sidetrack Treatment Results
Understanding formation petrophysics,
initial well treatment outcomes, and how

FIGURE 3A
Sidetrack Well with Productivity
And Fracturability Indices
(Yellow: Upper Woodford; Orange: Black Shale)

58 THE AMERICAN OIL & GAS REPORTER

reservoir conditions were altered by preexisting hydraulic fractures was necessary
to optimize the sidetrack treatment design.
During the initial well treatment, there
was a dramatic difference in the outcomes
of stages 17-22 versus other stages. These
stages encountered significantly higher
surface treating pressures (STPs) with
significantly lower treatment rates.
Figure 4A compares the ratios of
STP with treatment flow rates by stage
for both the sidetrack and the initial
well. This is a qualitative comparison
that affirms the difficulty of placing
treatments during certain stages. When
excessive treating pressures occur, the
responses can be interpreted as restricted
fracture geometry development-whether
a limitation on fracture lengths or widths-
making it difficult to place the designed
stimulation treatment.
The restricted fracture geometry could
be caused by a severe stress differential
across perforation clusters, the heterogeneity of the treatment intervals, the
presence of leak-off zones (natural fracture
networks), or some combination thereof.

FIGURE 3B
Sidetrack Engineered
Stage/Perforation Design
Compared with Geometric Design

American Oil and Gas Reporter - December 2017

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