White Paper
Steerable Drilling Liner Systems
Operators are experiencing and overcoming new challenges that only a few years ago would
have precluded them from completing the drilling process in many of today’s wells. Operators
recognize that drilling nonproductive time (NPT) is running at high levels. Accepting 30% drilling
NPT has become a rule of thumb in many difficult drilling environments, even reaching 45% in
some wells. Wellbore instability problems seem to be the main sources of NPT in problem wells.
Some operators have reported wellbore instability accounting for over 40% of their total NPT,
and some 25% of overall drilling costs in these difficult wells.
Subsalt applications, tar zones, and depleted zones are examples
of some of the problems routinely encountered that must be
overcome, often increasing NPT during the drilling process. While
advances have been made, these challenges continue to pose
significant risks for operators working to develop new discoveries.
Wellbore Stability – Drilling NPT
Low-Pressure or Depleted Zones
New zones in mature fields continue to be actively developed
as operators strive to maintain depleting reserves. Many of the
world’s new reserves are discoveries made below these existing,
mature reservoirs. Drilling activities in or near producing or
previously abandoned reservoirs often encounter large variations
in pressure gradient as depleted layers or under-pressured zones
are exposed during the drilling process. Zones with pressures
inconsistent with the overburden are often encountered, and the
uncertainty of pressure expectations in these wells can lead to
difficulties in well planning and managing mud systems due to
problems with lost circulation, sloughing, or collapsing formations.
If conventional drilling techniques are used, then the higher
mud weight used to hold back the target interval may result in
massive losses in the lower-pressure zone. To mitigate this risk,
the operator is often forced into a conservative drilling program
with reduced flow rates, lower weight-on-bit and diminishing
penetration rates or extra casing points.
4%
4%
3% 2%
5%
9%
cement
squeeze
geomechanics
and
pressure-related
incidents
37%
wait on
weather
14%
rig failure
22%
1. 37% NPT geomechanics/pressure1,2
2. equals 24% to 27% of total drilling costs2
3. estimated industry impact: $26Bn/yr3
References:
1. Welling & Co. (2009); Industry Survey
2. James K. Dodson Co. (2004); Incidences from 549 GoM
shelf wells (<600 ft water depth) between 1993-2002
3. Sweatman, R., Deepwater: Drilling Trouble Zones and
Well Integrity, RPSEA Forum at University of Southern
California, November 29th, 2006.
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2
Fig. 1: Typical salt dome in the Gulf of Mexico
Subsalt Formations
As the industry continues to push the limits of offshore
development in deepwater fields, an increasing number of
technological barriers emerge. In addition, more complex tighttolerance casing designs, subsalt formations, and problems
associated with them increase the operator’s risk of drilling in
these environments. These zones typically have unstable pore
pressures and can be prone to “creeping” as the pressures try to
normalize. This creep effect leads to highly unstable rubble zones,
which can severely hinder drilling efficiency.
Fig. 1 illustrates a huge salt dome typical of formations in the
Gulf of Mexico. It’s common for operators to drill 15,000 ft of salt
in deepwater wells. Rubble zones are usually found at the start or
at the end of the salt section, with the section at the end being
more troublesome.
These rubble zones cause borehole instability and can create
extreme vibration in the drillstring to a point where holes collapse
or bottomhole assemblies (BHAs) twist off. It’s common to drill
sidetracks after the initial BHAs are stuck when drilling out of
these rubble zones.
Maintaining the directional well plan can also become more
challenging in subsalt formations due to the vibration problems.
Instances of extreme drillstring vibration while drilling a salt or
subsalt section have prevented measurement-while-drilling (MWD)
or logging-while-drilling (LWD) systems from operating properly
and may require a trip to adapt the drilling assembly.
In such instances, having a stable drilling system where you can
case off the formation while drilling reduces considerable risk.
If done correctly, this could stand for the biggest drop in client
NPT in difficult wells.
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3
Tar Zones
Evolution of Casing and Liner Drilling Technology
One of the increasingly more common problems encountered in
subsalt environments is drilling through tar deposits. Significant
problems can arise due to the tar’s highly viscous and unstable
state in the formation. Tar typically is not rigid enough to be drilled
or broken into manageable pieces by the drill bit and its highly
viscous nature does not lend itself to be easily circulated out of
the wellbore in a liquid state. Initial encounters with tar during
the drilling process can range from few to no problems for thin,
segregated layers to significant difficulties drilling through thicker
zones. Extended, difficult tar zones have created torque problems
so severe that drillstrings have twisted off and wells have had to
be sidetracked to resume drilling operations.
When drilling in difficult downhole environments, the concept of
drilling with casing instead of conventional drillpipe gains favor
because it eliminates the need to expose the wellbore between
the drilling and casing processes. Running the casing string while
drilling helps mitigate many of the risks seen when a section
is drilled conventionally where the drillstring is removed from
the wellbore and a casing string must be run back into the
difficult section.
Even after successfully drilling through a tar zone, problems can
continue during subsequent drilling below the zone. Tar deposits
accumulate in stratigraphic traps below salt zones and can be
highly susceptible to flowing into the wellbore. This tendency to
flow into the wellbore creates additional stresses and difficulties
for the drillstring. Among these problems are drillstring torque
while drilling subsequent zones and more significantly, problems
re-entering the wellbore after a trip. These issues typically incur
NPT spent redrilling a tar section. After the drilling cycle, many
times openhole logging tools become stuck or there are problems
getting casing across these zones.
With steerable casing and liner technology, it is possible to drill
through these tar zones and isolate them when drilling. Once
casing is across the open hole, the overall risk profile of the well
is tremendously reduced. Many proposals to handle tar have
come forth over the years, but few successful solutions have
materialized. With steerable drilling liner (SDL) technology,
finally this may be possible.
The idea of drilling with a string of casing has been around for
more than 100 years, since Reuben Baker’s original patent in 1907
for a casing shoe used in cable tool drilling, which launched Baker
Oil Tools (now part of Baker Hughes). Various other technologies
and approaches have been used over the decades, but in general,
the main objective of each of them was to reduce flat time by
combining the casing and drilling into a single operation. Over the
last two decades, most applications focused on drilling liners into
depleted pay intervals with very high pore pressure differentials
and led to the use of casing and liner drilling to address the
drilling and completing of problem wells.
As global demand for hydrocarbon grows and easily accessible
reserves are depleted, the threshold of drilling technology
must continue to advance to allow operators to economically
drill in increasingly more difficult environments. Each year,
drilling engineers are routinely budgeting more and more time
for nonproductive drilling activities. The risks that were once
acceptable and expected in the drilling process are becoming less
tolerable and driving the development of technological solutions.
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© 2010 Baker Hughes Incorporated. All rights reserved. 29742
4
Casing Drilling
Drilling with a nonretrieved casing string has been successfully
applied for many years to address a variety of drilling issues, and
the known benefits are becoming more important in reducing the
overall drilling risks. Casing drilling ideas started as far back as
1890, but did not gain serious traction until the service industry
provided recent advances in technology. Fig. 2 shows that it
has been almost four decades since the first patent on casing
drilling was awarded. In its most basic form, casing drilling is
used to essentially drive casing into soft formations by circulating
and rotating the casing. The addition of basic cutting structures
on the casing shoe facilitates the procedure but still allows
harder formations to be drilled and for the shoe to be drilled
conventionally afterward, so drilling ahead can continue.
As the technology of casing drilling evolved, polycrystalline
diamond compact (PDC) cutting structures, specifically designed to
drill harder formation types, are now available for the shoe. While
the system does give the opportunity to drill new open holes, the
drawbacks to the system are that there is no steering capability
and no ability to get formation evaluation data while drilling.
Also, the string must be turned from the surface, which can
induce casing wear.
To counter some of the problems mentioned earlier, motor
technology had been used to help provide rotation to the bit
without having to rotate the casing. Although this helped reduce
casing wear, it did not address the issues of formation evaluation
and steering. Also, in this system, the motor and bit were attached
to the bottom of the casing and at total depth (TD) of the well, the
motor and the bit were left in the hole.
While motor drilling has advanced the technology for casing
drilling systems, the primary applications are typically vertical
sections with no directional requirements or logging requirements.
With today’s directional drilling and LWD technologies offering
distinct advantages in wellbore construction, many operators’
expectations require advanced capabilities beyond basic casing
drilling and drilling with mud motors.
As the steering needs
increased and the MWD/
LWD requirements also
increased, the casingwhile-drilling system (Fig.
3) provided the perfect
solution. With this system,
operators were able to
use state-of-the-art MWD/
LWD tools along with
rotary steerable tools to
drill complex profiles. When
the well TD was reached,
the BHA was extracted
using wireline tools. Even
horizontal wells have been
drilled with this system.
Additionally, in the event
of an LWD sensor failure,
the quick BHA retrieval using
wireline saves time for the
operator.
Fig. 3: Casing-while-drilling system
As this technology is gaining traction, so too is the need for a
steerable drilling liner system. A casing-while-drilling system
requires modifications on the rig to allow casing to be rotated.
There are much higher equivalent circulating densities (ECDs) due
to tolerances around the casing and also blowout preventer (BOP)
issues in deepwater projects.
Fig. 2: 1971 patent details from Brown Oil Tools on the first casing
drilling system
5
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© 2010 Baker Hughes Incorporated. All rights reserved. 29742
Liner Drilling
CASING/LINER - DRILL SHOE SYSTEM
(Simple bit below casing system)
The natural progression is from casing drilling to liner drilling.
Shoes with cutting structures allow for drilling new holes, but
they lack complex directional or logging capabilities. These
limitations lead to specialized applications where the difficult
section is drilled conventionally and the liner drilling assembly is
used to facilitate drilling the liner through the difficult section.
The advent of the SDL addresses the steering and logging
problems and creates new opportunities. As the system goes
through the initial stages of technology development, new
opportunities to drill previously undrillable wells will come
up. For example, applications may include drilling in tar zones
and depleted sands.
ADVANTAGES
DISADVANTAGES
LOW COST
SIMPLE TO OPERATE
NO RISK OF IRRETRIEVABLE
DOWNHOLE TOOLS
CEMENTING FOLLOWS UPON
REACHING TD
NO DIRECTIONAL AND LWD
CAPABILITIES
RIG MODIFICATIONS
REQUIRED
CASED HOLE LOGS ONLY
LIMITED DRILL SHOE
SELECTION
Fig. 4: Simple casing drilling system
Summary of Evolution
Casing and liner drilling applications can be placed into three
primary categories based on chronological development: the
simple casing drilling system; the casing drilling system with a
wireline-retrievable BHA; and finally, the latest SDL system
(Figs. 4, 5, and 6).
The first is simply a casing bit placed on a casing or liner
string to allow some simple drilling off of ledges, working the
casing through trouble zones or even drilling of new formation.
Quickly, there was a need for more power to the bit in hightorque operations and a motor inside the casing concept was
conceived. However, the drawback was that only minimal
steering could be done with this system and so, the emergence
of steerable casing while drilling took place. Today, dozens
of wells are drilled using the steerable casing-while-drilling
technology where a wireline-retrievable rotary steerable system
is used to drill a well. The third and latest application in this
paper uses a steerable BHA below the liner; this system allows
the operator to drill to TD and unlatch from the liner.
The advantages of this system are that it can be used with a
liner as opposed to a long string of casing, it requires minimal
rig modifications, and it reduces overall HSE risk.
All of the options must be carefully considered only after fully
understanding the particular drilling application. The SDL system
offers new, exciting prospects to the industry. There are no rig
modifications needed in the system, but additional development
is required to allow drilling and cementing of the liner in a
single trip.
CASING DRILLING - LATCH SYSTEM
(Motor below casing system)
ADVANTAGES
DISADVANTAGES
DIRECTIONAL AND LWD
CAPABILITIES
WIDE RANGE OF BIT
SELECTION
HIGH COST
RIG MODIFICATIONS
REQUIRED
RETRIEVABLE HOLE OPENER
LONG PILOT BHA (> 65)
RISK OF IRRETRIEVABLE TOOLS
(WIRELINE RETRIEVABLE BHA)
UNABLE TO CEMENT
IMMEDIATELY UPON
REACHING TD
Fig. 5: Casing-while-drilling system with wireline-retrievable BHA
Fig. 6: SDL system
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© 2010 Baker Hughes Incorporated. All rights reserved. 29742
6
Main Physical Components or Modules of the Steerable Drilling Liner System
Overall, the SDL system (Fig. 7) can be broken up into four different subsystems. The added advantage of the system is that most of the
components are already tried and tested systems with proven field reliability. The reamer drive sub that connects the inner string to the
reamer shoe is one of the only components developed specifically for this application.
Fig. 7: Complete SDL assembly
Outer String: The outer string (Fig. 8) consists of three main components: liner, setting tool and reamer bit.
Key advantages: All components are off the shelf. The reamer shoe itself is decoupled from the main liner body. This in turn
prevents the drilling vibrations from affecting the liner directly, thereby increasing the fatigue life of the liner.
Fig. 8: Outer string of SDL assembly
Inner String: The inner string (Fig. 9) consists of drillpipe and the inner BHA.
Fig. 9: Inner string of the SDL assembly
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7
Motor-Driven Components: The motor-driven components (Fig. 10) are the reamer bit and pilot BHA.
Key advantages: Having a motor downhole provides the advantage of not depending on surface pipe rotation, especially in
deep wells when downhole torque is a concern. Additionally, since the reamer shoe is decoupled from the main liner body,
we could conceivably think of a scenario when the bit is rotating at 150 RPMs and the liner at 30 RPMs. Without a downhole
motor, this would not be possible.
Fig. 10: Motor-driven components of the SDL assembly
Stick-out/pilot BHA: Fig. 11 depicts the stick-out of the SDL assembly, consisting of directional and formation evaluation tools.
Key advantages: In difficult trouble zones, the length of the stick-out needs to be minimized. The unique design of this
system helps achieve short stick-out lengths. The motor, the MWD pulser (BCPM), and the smart battery tools are all inside
the liner, thereby not adding to the stick-out length. Additionally, the modular nature of the LWD tools allows the use of
complex LWD technology to help geologists characterize reservoirs while drilling.
Fig. 11: Short stick-out of the SDL assembly
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8
Full-Scale Tests
Fig. 12: Experience with SDL System (all 4 images)
Simple profile
„„ Medium inclinations
„„ 6 × 8½-in.; 7-in. liner
„„ 1,064 ft
„„ Shale / sandstone / coal &
limestone beds
„„ Beta facility
„„
Simple profile
Low inclinations
„„ 8½ × 12¼-in.; 95/8-in. liner
„„ 406 ft
„„ Shale / sandstone / coal &
limestone beds
„„ Beta facility
„„
„„
Brage 31/4 A-13 A
0
250
Complex drop profile
„„ High inclinations
„„ 8½ × 12¼-in.; 7-in. liner
„„ 546 ft
„„ North Sea
30 inch
„„
500
0
0
250
TD 5,172m MD
500
750
1
Wellpath
SDL
7 inch
000
250
Ea1s
00
t (m15
0
) 175
200
0
0
225
Complex ERD profile
„„ High inclinations
„„ 8½ × 12¼-in.; 95/8-in. liner
„„ 590 ft
„„ North Sea
2
500
275
0100
0
750
500
250
N
0
h(
ort
True Vertical Depth(m)
250
9 5/8 inch
750
True Vertical Depth (m)
13 3/8 inch
250
500
750
0
100
0
5
12
0
150
0
5
7
1
0
200
0
5
2
2
0
250
100
0
150
0
200
250
0
0
225
0
250
0
275
m)
13 3/8 inch
0
125
175
20 inch
0
7 inch Liner
0
250
„„
Wellpath
SDL
500
Nor
th (
9 5/8 inch
7 inch
TD 3,264m MD
m)
750
100
0 500
250
250
0
Eas
t (m
500
)
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© 2010 Baker Hughes Incorporated. All rights reserved. 29742
9
Drilling on Land vs. Deepwater
Unlike other liner drilling systems that
deliver a combination of products from
several vendors, the Baker Hughes
steerable drilling liner system consists
only of integrated, reliable Baker Hughes
products and services. These trusted
technologies include:
AutoTrakTM rotary steerable system
A vital part of the BHA, Baker Hughes’ AutoTrak
rotary steerable system provides improved
performance and hole quality in directional
wells, and delivers continuous steering and
precise wellbore placement.
Modular formation evaluation suite
Several formation evaluation technologies can
be deployed on the BHA, providing geologists
with vital formation data as well as downhole
weight-on-bit and torque-on-bit information.
HRD-ETM setting tool
The pressure-balanced HRD-E setting tool
ensures reliable, trouble-free makeup and
allows for high-circulation pressures without
fear of premature release, while enabling high
torque for slow rotation during the drilling
process.
The choice of using a casing-while-drilling system or an SDL system depends
on the application. While both casing-while-drilling and SDL technologies
have successfully been used to drill directional wells, in deepwater
applications, casing-while-drilling technologies would require subsurface
BOP modifications and time-consuming operations on the rig floor. The BOP
modifications are mainly required because the casing will be constantly
rotated through the BOP stack. Additionally, during well control situations,
the BOP would need to be able to shear the casing that is currently being
used for drilling. Compared to that, SDL technology requires minimal
additional time while rigging up (false rotary table) and does not require
any BOP modifications. Currently, because of the limitations of the casingwhile-drilling systems mentioned above, few operators actually deploy the
casing-while-drilling system offshore.
Cost Savings with the Steerable Drilling Liner System
As mentioned before, care has to be taken to match the technology with
the right application to reap financial benefits. The following list of drilling
activities is required with conventional drilling, but could be eliminated or
minimized when drilling unstable formations with a new SDL system:
Extra reaming to ensure the hole is open
Extra circulating to ensure pore pressure balance is maintained
„„ Pumping of extra mud chemicals/additives to ensure hole stability
„„ Possible additional clean-out trips
„„ Pumping of extra mud in cases of losses
„„ Increased HSE cost when spending additional time on the rig and well
control issues when dealing with the above-mentioned activities
„„
„„
Over time, with the development of the one-trip system (drill, case, and
cement in one run), the SDL system will also be able to reduce trips and
further contribute to the bottom line.
PDC/core bits
Baker Hughes PDC and core bits consistently
drill longer footage through hard, abrasive
formations. These exclusive bit designs and
depth of cut-control technology deliver a highquality hole in the most challenging drilling
environments.
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10
Contact
Kathy Shirley
Corporate Communications Manager
Baker Hughes
2929 Allen Parkway, Suite 2100
Houston, Texas 77019
11
Tel +1 713 439 8135
Fax +1 713 439 8280
kathy.shirley@bakerhughes.com