American Oil and Gas Reporter - November 2015 - 102

SpecialReport: Marcellus/Utica Activity

Project Assesses 'Engineered Staging'
By Pascal Lim,
Peter Goddard,
John Sink
and Ibrahim Abou-Sayed

HOUSTON-Perforation clusters in
horizontal wells with multistage plugand-perf completions generally are designed with equal spacing and stage
lengths. Recognizing that a shale formation
is not homogeneous along a lateral section,
"engineered staging" is an alternative approach that takes geological and geomechanical properties into account. The goal
is to determine wellbore segmentation
during fracturing by grouping intervals
with similar properties to promote a
higher percentage of stimulated clusters
for improved production and recovery.
To examine the degree to which staging
and clustering can be optimized using
horizontal descriptions of key geological
properties, two pairs of horizontal Marcellus Shale wells were completed with
one well in each pair using engineered
staging and one well in each pair using
regular stages with equal spacing/lengths.
The well pairs are located in the Marcellus dry gas play in Pennsylvania. For
"group A," the A1 well was completed
with engineered staging based on openhole lateral logs, and the A2 well was
completed with regular staging. For group
B, the B1 well was completed with engi-

neered staging based on laterally projected
data from a nearby vertical pilot hole,
and B2 was completed with regular staging.
A comprehensive suite of open-hole
logs was run in the horizontal lateral of
A1, and the engineered staging was designed according to the rock properties
measured. The well was plug-and-perf
stimulated using slickwater. After 12
months, a production log was run to determine the downhole contribution of
each stage and cluster.
No open-hole logs (other than measurement-while-drilling gamma ray) were
run in the B1 well. Instead, properties
were extrapolated for (projected onto)
the horizontal section using logs acquired
in the adjacent vertical well. B1 then
was completed using engineered staging.
Cumulative production from both A1
and B1 exceeded that of their offset wells
after 400 days, potentially attributable to
the engineered design. In the case of B1,
production figures show a potential benefit,
but without the cost of acquiring logging
data in the lateral.
When stimulating several clusters of
equal spacing/length in a plug-and-perf
completion, any closure stress differential
between clusters theoretically will impact
the rate of fluid taken by the formation at
each entry point. Within the same stage,

FIGURE 1
Dual Oil-Based Mud Imaging Interpretation

102 THE AMERICAN OIL & GAS REPORTER

low-stress intervals can be expected to
take more fluid than high-stress intervals.
If the stress differential is high enough,
some clusters may not be stimulated,
leaving parts of the rock untouched. The
presence of natural fractures also can impact this flow distribution, since they
tend to be paths of lower resistance.
The purpose of engineered staging is
to group and stimulate clusters with
similar properties to obtain "balanced"
reservoir fracturing throughout the lateral.
This requires determining the rock's horizontal heterogeneity using geological
data. The two main parameters driving
perforation design are closure stress and
the frequency of natural fractures. The
third parameter is near-wellbore petrophysical properties, which also yield insights into the surrounding geology.

Logging, Data Extrapolation
Well A1 was drilled to 10,500 feet
measured depth, including 4,000 feet of
lateral section. It was drilled using synthetic oil-based mud and targeted a 20foot interval in the basal portion of the
lower Marcellus. The well was geosteered
using MWD gamma ray compared with
the bed thicknesses and gamma ray character of a vertical pilot well. Intermediate
casing was set at approximately 2,000
feet, and the final 8,500-foot section was
drilled at a 77⁄8-inch diameter.
After reaching total depth, a wiper
trip was run to assure the hole was in
good condition, and the open-hole logging
suite was run on drill pipe using a sideentry sub and latch system. Logging tools
used in the 170-foot string were:
* Integrated triple-combo;
* 3-D acoustic sonic;
* Elemental capture spectroscopy;
* Dual oil-based mud imaging; and
* Ultrasonic borehole imaging.
The logging program was designed to
provide comprehensive characterization
of near-wellbore properties and any variability along the lateral. The 5,400-foot
section logged included the entire lateral
and part of the curve. Data quality was
excellent overall, with the exception of
ultrasonic borehole imaging, where problems were encountered during the run.
Significant variability in log properties
existed along the wellbore. They were
interpreted to show variations in porosity,
total organic carbon, and geomechanical

American Oil and Gas Reporter - November 2015

Table of Contents for the Digital Edition of American Oil and Gas Reporter - November 2015