American Oil and Gas Reporter - August 2016 - 50

SpecialReport: Horizontal & Innovative Drilling

Study Analyzes High-Density Well Pads
By Mehdi Ostadhassan,
Siavash Zamiran,
Hadi Jabbari,
Abdolreza Osouli,
Bailey Bubach
and Ben Oster
GRAND FORKS, N.D.-Drilling
"megapads" with large numbers of horizontal wells, including high-density multilateral pads with multiple horizontal
branches radiating from the main vertical
borehole, seems inevitable to increase
the productivity of the Three Forks formation in the Williston Basin.
The ability to drill high-density multilaterals would not only increase production, but also reduce overall per-well
drilling and completion costs and allow
more efficient hydraulic fracturing operations. Another major benefit is reducing
surface impacts while developing a field
or acreage position.
However, accurate well placement and
design is a crucial task in development
projects with high well densities. Instability
problems results from stress interplay
among nearby wellbores, and tight well
spacing and stress shadowing effects can
dramatically disturb the in-situ stress environment.
To assess stability and stress variation
around the horizontal section of a highdensity pad design, a study was conducted
in the Continental Resources-operated
Hawkinson Unit in Dunn County, N.D.
Focusing on the Three Forks formation,

mechanical properties of the rock unit
such as Poisson's ratio, Young's modulus
and unconfined compressive strength
(UCS) were extensively analyzed using
both field data and lab experiments. These
parameters were then input into numerical
simulation software, along with the calculated in-situ stress data, for instability
analysis and geomechanical modeling.
The study also considered the suggested
well spacing between two horizontal wells
with respect to the direction of the principal
horizontal stress perturbation, as well as
failure zones in the horizontal section.
The late Devonian to early Mississippian Three Forks is one of the highestproducing layers in the Williston Basin.
Located beneath the Bakken formation
as part of the Bakken petroleum system,
the Three Forks consists mainly of thinly
interbedded greenish-gray and reddishbrown shales, light brown to yellow gray
dolostone, gray to brown siltstone, quartzose sandstone, and minor occurrences
of anhydrite. In the deeper part of the
basin, the Bakken/Three Forks contact is
comformable, while the contact appears
unconformable in basin flanks. The maximum thickness of the layer is about 250
feet in the eastern McKenzie County.
The Three Forks is informally subdivided into lower, middle and upper members, but Continental Resources-the most
active driller in the play-has divided the
formation into four different benches. Investigating retrieved cores from wells
drilled throughout North Dakota shows

FIGURE 1
Hawkinson Unit 'Megapad' in Dunn County, N.D.

50 THE AMERICAN OIL & GAS REPORTER

that the first and second benches (upper
and middle Three Forks) are present
throughout the basin. Consisting mainly
of sandy dolomite interbedded with green
shale, these two benches are the primary
drilling targets. The third bench is mainly
shale and anhydrite-dominant, and the
fourth bench is more locally developed
and could be missing in specific areas.
High-Density Pad Drilling
Multiwell pads have quickly become
the norm in the Williston and other unconventional basins. The ability to drill
four, eight or more wells on a single pad
provides significant operational and economic advantages to the operator. Multilateral and high-density pads with 10, 20
or more wells can reduce costs per well
by another 15-30 percent, including drastically reducing the number of days required to drill each wellbore to total
depth and increasing efficiencies in pumping fracturing treatments.
These techniques will lead to more
efficient land use and less environmental
disturbance. In fact, the smaller surface
disturbance is arguably the biggest advantage of high-density pads. Co-locating
a higher number of wells allows for fewer
roads and pipelines to access pad sites,
and the centralization of facilities such
as storage tanks, liquid separators and
vapor recovery units. The smaller footprint
also reduces vehicle traffic for ongoing
operations and maintenance activities.
The Hawkinson Unit "megapad" was
designed with 14, two-mile long horizontal
wells targeting multiple Bakken and Three
Forks pay zones (Figure 1). Four of the
horizontal wells target the Middle Bakken,
three target the first Three Forks bench,
four target the second Three Forks bench,
and three target the third bench of Three
Forks. The estimated initial monthly production rate from the 1,280-acre unit is a
combined 14,850 barrels of oil equivalent
from all 14 wells. The Hawkinson wells
are spaced 1,320 feet apart in the same
zone, and are offset 660 feet in the
adjacent lower or upper zones.
In situ vertical (overburden) stress and
two principal horizontal stresses (minimum
and maximum) had to be calculated to
build a mechanical earth model (MEM)
to run geomechanical simulations on the
Hawkinson wells. Poisson's ratio, Young's
modulus, UCS and other key mechanical

American Oil and Gas Reporter - August 2016

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