American Oil and Gas Reporter - February 2015 - 59

SpecialReport: Unconventional Resource Science
are propagating through the pay zone with
equal half-length (given almost equal
well spacing), the thinner fracture translates into less conductivity and, consequently, lower gas production. FTA and
WQA evaluations of the impact of Young's
modulus on performance in both three and
24 months of production reveal that those
wells with higher Young's modulus show
lower performance than those with lower Young's modulus.
With regard to another parameter,
minimum horizontal stress, it is a proven
fact that a horizontal well should be
drilled parallel to minimum horizontal
stress, while the hydraulic fractures tend
to initiate parallel to maximum horizontal stress. Rock mechanical studies show
any increase in minimum horizontal stress
shrinks created hydraulic fracture width
and harms performance. A look at the
reservoir's minimum horizontal stress
distribution shows that areas with higher
minimum horizontal stress are less favorable for creating wide and more conductive fractures.
However, this study's FTA and key performance indicator (KPI) analyses do
not confirm this theory. This contrast
could be attributable mainly to the fact that
this study does not perform sensitivity
analysis on a known physic-based simulation model. We are dealing with the actual, nonlinear system. Therefore, in that
area of the reservoir, other parameters play
more important roles-such as fracture
quantity and reservoir characteristics-and
shadow the impact of minimum horizontal stress on production performance.

Then there is the parameter of Btu area.
Based on the content of condensate, the
Marcellus Shale study area was divided
into four Btu areas varying from dry, low
Btu, to wet, high Btu, regions. Figure 3
shows the estimated distribution map of
Btu area. According to this figure, the
reservoir's eastern part, in which most
wells have been drilled, are located in the
dry/low Btu area.
Analysis shows the wells in the reservoir's eastern part perform better than those
in its western area. Although they are located in a wet/medium Btu area, WQA
analysis shows these wells do not perform
as strongly as wells in the dry/low Btu area,
which categorizes them as "poor" and "average" wells. It is worth mentioning that
the Btu area is a discrete parameter for
which the database sets numeric values
from one to four. Therefore, no KPI
analysis can be done for this parameter.
Design Parameters
Regarding the parameter of deviation
type, each of the dataset's wells are identified according to whether they deviate up-

FIGURE 4
WQA Deviation Type for Different Well Clusters at 3 (Left)
And 24 Months (Right)
Categorized Based On: Rich Gas-3 Months-Mcf
Deviation Type

Poor Wells

Average Wells

Good Wells

Categorized Based On: Rich Gas-3 Months-Mcf
G1-InDIs

Poor Wells

Average Wells

Good Wells

2,450
2,400
2,350

2,300

2,200

Average

Categorized Based On: Rich Gas-24 Months-Mcf
G1-InDIs

2,500

2,100

2,250
2,200
2,150
2,100

2,000

1-Dry

All Data

2,400

2-Low

3-Medium

Deviation Type from
Up-Dip to Down-Dip

FIGURE 5
WQA Inside Distance for Different Well Clusters at 3 (Left)
And 24 Months (Right)
2,500

4-Wet

Categorized Based On: Rich Gas-24 Months-Mcf
Deviation Type

Deviation Type from
Up-Dip to Down-Dip

All Data

FIGURE 3
Btu Area Distribution Map

dip, downdip or do not dip. The WQA
analysis exhibited in Figure 4 clearly
shows that, in this part of the Marcellus,
both early and late well performance is favorably impacted by downdip well deviation. The downdip wells are either completely or partially fractured in the Lower Marcellus, which is more prolific in
terms of reservoir characteristics and net
thickness.
Inside distance is another parameter.
Most Marcellus laterals are spaced from
1,000 to 2,000 feet, even though some operators have experimented with closer
spacing. To investigate the impact of distance between laterals, the inside distance
parameter was defined as the distance between the laterals from a multiwell pad.
Early in production, lower inside distances
between laterals translate into more stimulated reservoir volume and better productivity.
A relationship also can be observed later in a well's life, except that greater distances between laterals in older wells elevates their production. In this situation,
shale wells act like conventional wells and

2,050
2,000

1,900

1,950
All Data

Poor Wells

Average Wells

Good Wells

All Data

Poor Wells

Average Wells

Good Wells

FEBRUARY 2015 59

American Oil and Gas Reporter - February 2015

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