American Oil and Gas Reporter - January 2012 - 87

Oil & Gas Shales

Geosteering Improves Bakken Results
By Kevin O'Connell,
David Skari,
Aaron J. Wheeler
and Allan Rennie
DENVER-Developing tight oil and
gas-bearing formations often requires a
dense pattern of wells with long lateral
sections. To produce such fields economically, producing sections of wells must
be positioned accurately within the targeted
intervals, while drilling costs are kept to
a minimum.
A cost-effective solution has been developed that includes predrill modeling
of logging-while-drilling measurements
along the trajectory of a planned well to
compare with real-time LWD data. This
provides the ability to support geosteering
to and within the target formation. This
geosteering technique has been utilized
to develop Bakken Shale oil assets. The
wells have been navigated to land consistently in the reservoir, and have successfully
maintained position within the primary
target zone for more than 90 percent of
the lateral sections.
North Plains Energy LLC (NPE) is a
Denver-based company focused on acquiring, developing and enhancing oil
and gas assets within the continental
United States. NPE operates acreage in
part of the Williston Basin on the west
flank of the Nesson Anticline. A 2008
U.S. Geological Survey assessment of the
undiscovered resources in the Upper Devonian-Lower Mississippian Bakken formation of the Williston Basin Province in
Montana and North Dakota estimated
mean undiscovered volumes of 3.65 billion
barrels of oil, 1.85 trillion cubic feet of
associated natural gas, and 148 million
barrels of natural gas liquids.
NPE is drilling and developing two blocks,
aggregating approximately 50,000 net acres
in the heart of the Bakken Shale in Divide,
Williams, Dunn and McKenzie counties,
N.D. (Figure 1). Led by a highly experienced,
technologically focused management team,
the company prides itself on customizing its
drilling and completion methods to the
unique geological and geophysical characteristics of its core project blocks.
Drilling History
Since early in 2010, Ensign Rigs Nos.

89 and 118 have been working for NPE
in Divide, Williams and McKenzie counties. Wells are being drilled to target zones
located between 9,000 and 11,000 feet
true vertical depth. The horizontal producing sections of the wells average 8,000
feet of lateral, which is cased, perforated
and fractured in multiple stages. The two
primary intervals targeted within the oil
reservoir are a clean dolomite member of
the Three Forks formation and a 15-foot
zone below a tight limestone within the
Bakken Middle Member.
Initially, the horizontal production wells
required drilling a vertical pilot hole that
was sidetracked, deviated from vertical
to build the curve, then drilled laterally
within the producing zone. Wireline logs
and cores were run in the initial pilot
hole to determine the landing point for
the sidetrack and to evaluate the optimal
interval within the reservoir to target.
There was limited regional structural
control in planning the laterals. The initial
well required a sidetrack because it inadvertently drilled into the Upper Bakken
FIGURE 1
North Plains Energy LLC Area of
Operations in North Dakota

Shale. NPE decided that a single geosteered
well trajectory would be more cost effective, and the resulting smoother well
profile should reduce the risk of losing
the bottomhole assembly. It also would
make the completion less problematic. In
addition, using LWD tools in the region
would provide valuable experience and
knowledge about the subsurface geology
of the target formations while drilling.
Geosteering Partnership
Prior to geological steering methods,
the success of a directional drilling operation depended largely on steering the
well through a target reservoir with an
assumed position fixed in geometric space.
However, a success in geometric terms
could be a failure in economic terms if
the assumed and actual geometric locations
of the reservoir differed.
Effective well placement in horizontal
drilling requires that geological changes
be detected quickly, and that the well
plan be adjusted in a timely fashion. With
this challenge in mind, a dependable geological steering partnership was developed
between NPE and PathFinder, a Schlumberger company, for providing directional
drilling and MWD/LWD services, supported by the company's PayZone Steering™ services at the well site. The realtime forward modeling software assists
in geologically steering deviated well trajectories by combining petrophysical data
from LWD logs run in offset wells, the
geological earth model, and the directional
well plan to create a model of the formations being drilled.
During the early stages of the project,
service company staff, working in close
consultation with the operator's technical
team, focused on learning the geologic
setting in the area. Effective communications among the team allowed it to assemble local earth models based on available seismic data, structural information,
and information from selected offset wells.
Wireline and LWD data from offset wells
were utilized to calculate the expected
LWD response of formations into which
horizontal wells were to be drilled. LWD
data types typically modeled included
gamma ray, resistivity, density-neutron
(imaging), and sonic measurements.
JANUARY 2012 87

American Oil and Gas Reporter - January 2012

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