American Oil and Gas Reporter - January 2017 - 62

Shale Resource Science
FIGURE 2
Average Lateral TVD and Toe-Up/Toe-Down Wells
1,900

365-Day Cumulative Gas Production (MMcf)

To address the possible impacts of
well orientation on productivity and
overall economics, Devon Energy Corp.
conducted an in-depth integrated analysis
of the performance of wells with both
toe-up and toe-down lateral orientations
in its Cana Woodford operating area in
west-central Oklahoma. The study correlated the change in lateral total vertical
depth (i.e., the change from the heel to
the toe of a horizontal well, or toe up
versus toe down) to three measures of
horizontal multistage fractured well production performance:
* 90-day initial productivity;
* 365-day cumulative totals; and
* Estimated ultimate recoveries.
The analysis included a dataset of
more than 300 Cana Woodford horizontal
wells located within a three-township area
to isolate production performance drivers
such as reservoir conditions, geology,
stimulation size, etc. A dataset of this
size contained within a small, homogenous
area allows for superior statistical control
and results. Using a "real-world" dataset
to create isolated variable groups enabled
Devon to analyze the effect on production
of changes in lateral TVD independent
of other factors.
The analysis revealed a relationship
between lateral TVD change and production performance. In the dataset analyzed, lateral TVD change was shown to
have a significant effect on production
performance. The impact of the relation-

1,800
1,700
1,600
1,500
1,400
1,300
1,200
1,100
1,000
900
800
700
600
500
400
300
200
100

r2=0.375

11,600

11,800

12,000 12,200

12,600 12,800
Average (TVD)

Toe-Down

ship between lateral TVD and production
performance also changed, based on reservoir conditions.
The study results indicate that toedown wells were the lowest-performing
group, followed by flat wells, and then
toe-up wells. Not only were toe-down
wells poor performers, but the more
severe the toe-down inclination angle,
the poorer the production performance.
Wellbore orientation (toe-up/toe-down)
is dictated by the combination of surface
location and the direction of the well
with relation to geologic bed dips. In an
effort to maximize contact with pay, wells
are steered to follow these natural angles

FIGURE 1
Toe-Up versus Toe-Down Well Orientations
Toe-Up

12,400

Toe-Down

13,000

13,200

13,400

13,600

13,800

Toe-Up

and contours. Figure 1 shows a schematic
of typical toe-up and toe-down wellbore
trajectories with reference to the bed dips.
For the Cana Woodford analysis, a
toe-up well was defined as a horizontal
well with an average inclination angle
greater than 90 degrees and a negative
lateral TVD gain (the TVD change between
the toe and heel of a horizontal well),
while a toe-down well was defined as a
horizontal well with an average inclination
angle less than 90 degrees and a positive
lateral TVD gain. For purposes of the
study, each well's TVD was averaged
along the length of the lateral, and its inclination angle was averaged along the
entire length of the lateral. Gross lateral
length was defined as measured depth at
the toe minus measured depth at the heel.
Study Workflow
The methodology and workflow steps
for the Cana Woodford study consisted
of collecting data, identifying primary
and secondary variables, binning data,
analyzing the data, and then using the
results to impact economic decisions.
A great amount of data is needed in
order to fully understand what is driving
well performance and to decrease the

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American Oil and Gas Reporter - January 2017

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