American Oil and Gas Reporter - July 2017 - 69

SpecialReport: Horizontal Wellbore Construction
A level 3 junction has a cased/cemented
main bore and a liner isolating device in
the junction to provide mechanical support.
The liner device typically has an oriented
pre-milled window opening to allow
access back to the main bore, and a
milling system is used to cut a casing
window to directionally drill laterals.
Most level 3 multistage fracturing completions consist of open-hole sleeves combined with an open-hole packer for stage
isolation. Typically, the entire completion
is run and tied back to the main bore and
all the packers and hangers are set before
releasing the rig and moving in a frac
spread to begin multistage treatments.
A level 4 junction has a cased/cemented
main bore combined with a cemented
liner in the junction to provide cement
isolation and mechanical support. Some
level 4 versions use level 3 junction equipment, but add cement. Another solution
is to cement the liner in place with the
liner top near the top of the window, removing the portion of the lateral liner top
in the main bore. Level 4 eliminates any
open-hole formation area in the junction
and provides easier access to the lateral
liner. Because the junction is cemented,
level 4 is better suited for plug-and-perf
or cemented liner fracturing. An openhole fracture completion, combined with
an inflatable packer and stage tool, can
be used to stage cement the junction area
to get the benefit of level 4 design.

Initial Field Applications
Several operators have experimented
with multilateral technology in unconventional reservoirs in North America,
and have deployed various types of junctions as well as lateral entry options for
completion and stimulation. In many
cases, the operators have documented
cost savings and environmental improvements when transitioning to pads with
multilateral architectures. These initial
applications also have identified some of
the key design issues and operational considerations for drilling, completing and
producing multilaterals in resource plays.
One example of a multilateral application in a resource play is a 25-well
program that SandRidge Energy executed
in the Mississippian Lime play using
open-hole sidetracks and cased-hole whipstocks to initiate the multilaterals. The
wells used various configurations, and
validated the mechanical feasibility, economic and production benefits associated
with multilateral development in the play.

Other examples are a Cimarex Energy-operated project in the Granite Wash
in the Texas Panhandle that constructed
dual level 4 junctions drilled from a
single vertical wellbore, and Penn West
Exploration's dual-lateral development
program using open-hole junctures and
open-hole multistage systems in the Slave
Point tight oil play in northern Alberta.
In assessing the economics of a multilateral project, the cost of drilling additional vertical sections has to be compared
with the cost of building junctions for
the multilaterals. For example, consider
the case for drilling and completing two
single horizontal wellbores from a pad
versus a dual-lateral wellbore. The higher
the cost of the vertical section of each
horizontal well, the more competitive becomes the cost of creating a multilateral
junction and isolating it for stimulation.
As with a single horizontal well, a multilateral requires a minimum of a drilling
rig, a frac spread and a coiled tubing unit.
However, how the well is drilled, completed
and stimulated determines how and when
this equipment is used, and how long it is
required on location. In some cases, a
workover rig could be used instead of a
drilling rig for certain operations. On the
other hand, the contiguous use of a fracturing
spread, CT unit and workover rig also
could be necessary, which would obviously
impact the bottom line.

Design Considerations
Should reservoir pressures require a
barrier to be installed after each lateral is
stimulated to protect against working in
a "live well" scenario, it could require
lubricator risers, a CT unit and a crane to
either remove or drill out the temporary
barriers. It may be possible to use a CT
indexing tool to retrieve barriers to stimulate additional laterals. If not, a
diverter/deflector will have to be installed
to gain re-entry into additional laterals,
requiring a workover rig.
Mobilization/demobilization costs can
be a factor in determining the economics
of drilling and completing a multilateral
well. The impact of rig moves on overall
project economics are a bit of an unknown,
since each operator schedules rig moves
relative to mobilizing frac spreads a bit
differently. For pad drilling, however,
optimized rig and frac spread moves can
be managed to effectively minimize mobilization/demobilization costs without
drastically impacting overall authorization
for expenditure (AFE).

Planning multilateral well subsurface
activities requires the same stringent approach to drilling and completion as a
single horizontal well, with some caveats.
Given that multiple lateral legs are created
from a single well, there is a greater need
for nontortuous wellbores, good hole cleaning practices, accurate pipe tallies, highlevel torque and drag modeling, and accurate
force and stress calculations. In addition
to sound operational procedures, it is critical
to ensure that surface equipment and facilities can support the multilateral wellbore
construction activity. This includes having
load and torque capabilities to accommodate
milling operations and setting/releasing
various temporary packer-based BHAs,
whipstocks, diverters, deflectors, etc.
Window quality and window milling
issues has been a concern for some operators that have experimented with multilaterals. Constructing long, straight windows and ensuring debris removal are
crucial for getting completion strings and
centralized liners into the laterals in level
2, 3 and 4 junctions. Some operators
have attempted to use level 2 junctions
with one-trip whipstock milling systems,
but have had to make second mill runs to
extend window openings to get liners or
completion strings to depth, or revert to
level 1 completions because of window
issues. A cement log should be run to
ensure the window kickoff area has satisfactory cement. If not, a squeezed cement
operation should be performed before
milling begins.
r

DOUG G.
DURST

Doug G. Durst is a global technology
adviser for Halliburton in Houston.
His diversified industry background
spans drilling, completion and production, and he has been associated
with a number of service companies,
with responsibilities ranging from product and business development to project
management. Durst holds multiple
patents. He has a B.S. in engineering
from the University of Houston.
JULY 2017 69

American Oil and Gas Reporter - July 2017

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