D R I L L I N G CONTRACTOR
DRILLING
Official Magazine of the International Association of Drilling Contractors
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OFFICIAL MAGAZINE OF THE INTERNATIONAL ASSOCIATION OF DRILLING CONTRACTORS
DOWN BUT
NOT
OUT
NORTH SEA WARMS
UP FOR REBOUND
Many optimistic that
a return to higher
activity levels is
coming into sight
INNOVATING WHILE
DRILLING
JULY/AUGUST 2009
• High-pressure riser,
20,000-psi subsea
wellhead system
among HPHT advances
• Monobore wells: the
pros and cons
• Proposing a new well
design model for GOM
deepwater
A L L
D R I L L I N G ,
A L L
C O M P L E T I O N S ,
A L L
T H E
T I M E
I N N OVAT I N G W H I L E D R I L L I N G
Continuous improvements lead to Maersk Oil
Qatar’s longest horizontal well in the world
By Kumud Sonowal and Bjarne Bennetzen,
Maersk Oil Qatar AS; Patrick Wong, K&M
Technology Group; and Erhan Isevcan,
Schlumberger D&M
MAERSK OIL QATAR AS (MOQ)
completed drilling the world-record
BD-04A well in May 2008 offshore Qatar.
It was the successful outcome of engineering efforts to increase extendedreach capabilities.
MOQ started to develop the Al-Shaheen
Field offshore Qatar in 1994 with horizontal drilling techniques pioneered by
Maersk Oil & Gas AS in the North Sea.
In May 2008 the BD-04A well was completed with a record horizontal length
of 35,770 ft. This well also set world
records for the longest well at 40,320 ft
MDRT and the longest along-hole departure of 37,956 ft.
The BD-04A well turned out substantially longer than planned. The original TD was
programmed at 28,850 ft and was later extended to 40,320 ft
mulation, 2) poor productivity of vertical
wells, and 3) number of platform locations required if a conventional approach
with vertical or slant wells was pursued.
The length of these horizontal wells has
been extended during the course of the
development, and some of these wells
are pushing the limits of what can be
achieved with today’s technologies.
This case study will review the history,
challenges and planning through the
drilling of the well. It will outline the
achievements, practices and engineering
analysis of field data where key learning
points have been shared. It will show
that even when constrained by limitations such as rig capacity, major stepchanges can be achieved by optimizing
basic operating parameters.
In 1994, when Well ALS-3 was drilled to
16,061 ft in the Al-Shaheen field, it was
a record-breaking well with a horizontal
length of 10,220 ft. This was achieved
with conventional directional drilling equipment such as mud motor and
adjustable gauge stabilizers; rotary steerable technology was not available yet.
BACKGROUND
MOQ operates the Al-Shaheen Field,
Block 5, under a production sharing
agreement with Qatar Petroleum (QP) .
The exploration and exploitation rights
include all Block 5 geological formations
above the Khuff formation.
The main targets comprise the Lower
Cretaceous Kharaib B and Shuaiba carbonate formations and the Nahr Umr
sandstone. The Kharaib Formation is
a laterally uniform carbonate deposition. Its thickness is generally 80 ft, with
a reservoir target of some 25 ft. The
Shuaiba Formation exhibits lateral facies
changes and permeability contrasts.
Its thickness is generally 200 ft, with a
reservoir target of some 20 ft. The Nahr
Umr Formation is a 20-ft sand sequence
with reservoir targets of some 5 ft or less
of permeable sand.
The decision to develop using long-reach
horizontal wells was primarily driven
by 1) the large aerial extent of the accu-
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July/August 2009
pursue new technologies and innovation
in its well design and operations, eventually leading to the record-breaking
BD-04A well.
BD-04A WELL
The well set two major world records:
(1) At 40,320 ft MDRT, it is the longest
well ever drilled, hence also achieving the longest reach of 36,238 ft.
(2) The longest horizontal section of
35,770 ft (i.e., from the first survey
above 86.0° inclination at 4,550 ft
MDRT to TD at 40,320 ft) with 35,449
ft of continuous reservoir exposure (9
5/
8-in. casing shoe at 4,871 ft).
The evolution of equipment and procedures has aided the expansion of extended-reach drilling in the Al-Shaheen Field.
There has been an ongoing development
of solutions to new problems at each
additional step-out in well displacement.
As new tools became available, fit-forpurpose technology was applied and
additional reach accomplished.
In addition to breaking the record length,
BD-04A achieved other milestones:
To further enhance the oil recovery
from the Al-Shaheen Field, MOQ in 2007
accepted the new challenge of drilling
even longer wells and initiated measures
with detailed engineering analysis to
expand the horizontal extended-reach
drilling envelope beyond the industry
experience. The approach of continuous
“pushing the limits” sustains the drive to
• Longest acid stimulation job (17,610
bbl of acid used).
• Longest 8 ½-in. section of 35,449 ft.
• Longest length drilled with a rotary
steerable BHA and LWD.
• Highest reach vs TVD (ERD) ratio of
10.48.
• Highest Directional Difficulty Index of
8.279.
BD-04A OPERATIONS
The BD-04A well is a line-drive pattern
producer targeting the Kharaib, KB-1a
D R I L L I N G CONTRACTOR
Reprint DC (Drilling Contractor) © July/August 2009
I N N OVAT I N G W H I L E D R I L L I N G
This graph provides a vertical section view of the BD-04A well path.
reservoir sub-unit along the entire horizontal section. The objective of this well
was to drain the area south of the BA-33
Kharaib well. It is the southernmost
producer in the line-drive pattern of the
current development phase.
BD-04A was substantially longer than
planned. The original TD was programmed at 28,850 ft. However, that was
extended to 40,320 ft to appraise the
eastern flank of the B-location and to
increase the exposure of single well in
the reservoir. A controlled 35° azimuth
turn was made as per the revised /
extended plan to align the well with the
next development phase line-drive pattern wells.
THE RIG
BD-04A was drilled within the limits of
a relatively small rig package. It had 2 x
1,600-hp pumps with an effective surface
pressure limit of 4,000-4,200 psi and a
TDS-4H top drive capable of 40,000 ft-lbs
of torque at 120 rpm. The derrick racking capacity is limited to about 17,000 ft,
or 181 triple stands of 5-in. drill pipe.
TOP HOLE SECTIONS
The catenary well profile (with a planned
dogleg of 3.0°/100 ft maximum) in the
top 16-in. and 12 ¼-in. hole sections was
drilled utilizing push-the-bit rotary steerable assemblies and optimally landing
the well horizontally (89.8º inclination)
in the target Kharaib reservoir at 4,881
ft MDRT (3,482 ft TVDRT). The 9 5/8-in.
casing shoe was set at 4,871 ft. The
advantages of using the rotary steerable
in these sections are smooth wellbore
curve, less tortuosity, good hole cleaning
and the ease of running casing.
RESERVOIR HOLE SECTION
The mud used in the 8 ½-in. reservoir
hole section was a non-formation damaging low-solids non-dispersive (LSND)
water-based mud system weighted to
9.3-9.6 ppg with sodium chloride (NaCl)
or calcium carbonate (CaCO3). Rheology,
especially low-end rheology, was maintained using Duotec to ensure good holecleaning properties. Static and dynamic
fluid loss was controlled with PAC-UL
and Polysal in the initial build phase
and thereafter maintained with Polysal
throughout the section. On several occasions, the use of high-viscosity sweeps
for improved hole cleaning proved to be
efficient in this section.
The LSND mud system exhibits two
important characteristics that are critical to the success of the well: a) hole
cleaning was fairly easy to achieve and
b) more importantly, hole enlargement
with time (BD-04A and offset wells have
consistently shown hole enlargement up
to average hole size of 9 ½ in. to 10 in.,
either inferring from lower equivalent
circulating density (ECD) values from
PWD logs or direct measurement from
ultrasonic caliper logs). This is integral
to ECD and torque management.
This graph plots the industry extended-reach drilling experience worldwide, overlaid
with the BD-04A well path.
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July/August 2009
After initial problems maintaining the
required azimuth direction when drilling
out of the 9 5/8-in. casing shoe at 4,871 ft
to 5,392 ft MDRT, an early sidetrack had
D R I L L I N G CONTRACTOR
Reprint DC (Drilling Contractor) © July/August 2009
I N N OVAT I N G W H I L E D R I L L I N G
to be made just below the shoe. The sidetracked hole was then drilled in two BHA
runs to the record TD of 40,320 ft.
The first part of the 8 ½-in. horizontal
reservoir section to 23,630 ft was drilled
at an average ROP of 221 ft/hr with
the push-the-bit rotary steerable and
insert bit. Downhole static losses were
reported at 8-12 bbls/hr. Geosteering
with assistance from LWD data was
applied to keep the well within the TVD
tolerance and place the well in the target
reservoir. Drilling torque friction factor
started relatively high when drilling out
of the casing shoe; however, it stabilized
between friction factor of 0.20-0.25. Stick
slip varied between 30-290 peak-to-peak
RPM difference. If torque friction factor
remained at 0.25, TD would have been
torque-limited to 27,000 ft with the 5-in.
drill pipe with API connections.
Lubricant was added from 20,500 ft
onwards at 2% concentration initially.
Torque friction factor improved to 0.190.21 after the addition of lubricant in the
mud system.
At 23,630 ft (after drilling 18,859 ft of
8 ½-in. hole), communication with the
rotary steerable tool was lost, and the
BHA was pulled out of hole.
This graph shows record wells by Maersk Oil Qatar. In 1994, 10,220 ft was the longest
horizontal length drilled by MOQ.
At this point, it was decided to extend
the TD of 28,850 ft. Torque and drag
modeling indicated that the expected
torque loads at the extended TD would
exceed the capability of the drillstring
and top drive; ECD loads would also be
prohibitively high if drilling was continued with the 5-in. drillstring, even with
hole enlargement to 9 ½ in. Further
modeling indicated that a tapered drillstring of 4-in. by 5-in. drill pipe would
be acceptable for torque and ECD loads.
Using a 4-in. by 5-in. tapered drillstring,
however, would result in higher pump
pressure and reduced flow rate at TD.
The length of the 4-in. drill pipe was
critical in order to balance these conflicting needs.
D R I L L I N G CONTRACTOR
Reprint DC (Drilling Contractor) © July/August 2009
July/August 2009
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I N N OVAT I N G W H I L E D R I L L I N G
Further evaluations were made to
prioritise the needs, and a balance
was struck with approximately 7,000
ft of 4-in. drill pipe in a tapered drillstring design. As part of the torque
mitigation efforts, 15,000 ft of 5-in.
19.5-ppf drill pipe with high-torque
connections were also included in
the top part of the drillstring.
thick and faulted. It was applied
through the entire reservoir section
with assistance from LWD data.
Formation evaluation information
such as gamma ray, azimuthally
focused laterolog resistivity, bit
resistivity, porosity and bulk density were utilized to make real-time
geosteering decisions. At the TD of
40,320 ft, mud pulse signals from
MWD and LWD were still transmitted and detectable using standard
equipment. The data rate of transmission was reduced from 3 bps
to 1.5 bps from 35,000 ft onward to
improve the data quality.
A point-the-bit rotary steerable BHA
was selected as it requires much
less pressure drop across the tool
to operate compared with a pushthe-bit system. Larger nozzles TFA
were also selected for the bit, further
improving the pump pressure and
flow rate at TD.
KEY ENABLING CHANGES
Another key to maximizing the
performance of the rotary steerable BHA was reducing downhole
shocks and vibrations to minimize
the negative effects on tool life and
to increase overall ROP. It was tried
to reduce vibrations (stick-slip,
BHA whirl, torque, etc) with drilling
parameters initially, and lubricant
was used in the mud system.
Drilling the BD-04A well to 40,320 ft
would not have been feasible prior
to MOQ’s initiative in late 2007 to
review the reasons for reach limitations in the Al-Shaheen Field. The
aim of the review was to expand
This plot shows BD-04A’s measured off-bottom and reach capability as the need for
drilling torque in the 8½-in. reservoir hole.
longer-reach wells may arise in
the future development phase of
The lubricant concentration was
Al-Shaheen.
increased from 2% to 3% at 28,000 ft.
A drilling mechanics log was also
The increase was necessary not only for
The 2007 review, amongst others, indiobtained for better understanding of
torque reasons but also to reduce the
cated that both reach and ROP in an
the causes of vibrations. The downhole
severity of stick slip for ROP improve8 ½-in. hole section, at that time, were
assembly provided comprehensive data
ment and preservation of downhole tools. constrained by drill pipe connections
for real-time and post-job analysis
Drilling torque friction factor did not
torque capacity and ECD loads, rather
of drillstring dynamics. This process
show significant improvement when the
than top drive or rig capability.
enabled development of drilling practices lubricant concentration was increased.
As a result, de-bottlenecking efforts
to reduce downhole shocks and vibraA 35° azimuth turn to the right was exe(designing the tapered drillstring) began
tions that ultimately enabled developing
cuted as per the extended-TD well path
with acquiring 5-in. drill pipe with higher
correlations between surface and downfrom 33,500 ft to 36,000 ft to align the
torque connections, as well as the introhole WOB and torque for use in future
well with the next development phase
duction of a section of 4-in. drill pipe.
ERD wells.
line-drive pattern wells. While drilling
These equipment upgrades contributed
The 4-in. by 5-in. tapered drillstring with
ahead at 36,630 ft, the drilling torque
to the success of BD-04A. The net and
point-the-bit rotary steerable BHA was
peaked to 36,000-39,000 ft-lbs (average
immediate benefits after the combination
tripped in positive weight to 22,376 ft
prior was 32,000-33,000 ft-lbs). This coin- drillstring was picked up are listed in
and reamed/washed down to bottom due
cided with higher lost-circulation rates
Table 1.
to negative weight. Drilling continued
experienced at that depth.
The critical changes that allowed this
ahead from 23,630 ft to 33,877 ft at an
The torque peak was probably due to
extraordinary reach to be achieved are:
average ROP of 120 ft/hr. Drilling torque
azimuth turn. A precautionary wiper
was tracking between friction factor of
• Drill pipe upgrades to high-torque contrip was made to 33,500 ft and washed/
0.18-0.21, which was to be within the top
nection to maximize the torque capabilreamed down to bottom. Drilling
drive limit when projecting ahead at the
ity of the top drive.
resumed
at
an
average
ROP
of
120-135
extended TD. Stick slip averaged 30-290
ft/hr and drilling torque of 32,000-35,000
peak-to-peak RPM difference. Downhole
• A tapered drillstring design with slim
ft-lbs (friction factor of 0.18-0.21) to the
static losses increased to 25-34 bbl/hr
OD drill pipe in the lower part, for torque
TD of 40,320 ft.
from 26,600 ft onwards.
loads reduction, as well as ECD improveAt 33,877 ft, a wiper trip was performed
to 18,307 ft to reposition the high-torque
drill pipes. The drillstring was then
tripped in positive weight to 26,585 ft
and reamed/washed down to bottom. The
ability to trip in positive weight to 26,585
ft indicated that the hole condition was
good.
Geosteering is critical to drill and position the wellbore in the target formation
as the reservoir is approximately 10 ft
Drillstring
ment. Slim-OD drill pipe have the added
benefit of slightly reducing friction factor.
Drilling Torque (kft-lbs) Friction Factors ECD (ppg)
5” drill pipe string
19 - 26
0.20 - 0.24
15.2
5” X 4” drill pipe combination
14 - 21
0.18 - 0.21
14.3
Table 1: The new drillstring brought immediate benefits to the drilling operation.
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July/August 2009
D R I L L I N G CONTRACTOR
Reprint DC (Drilling Contractor) © July/August 2009
I N N OVAT I N G W H I L E D R I L L I N G
• Use of lubricant in the mud system for drilling torque and stick slip
mitigation.
BD-04A was terminated at 40,320
ft due to logistical reasons and
after a thorough risk assessment.
The torque loads were still within
the capability of the drillstring
design, top drive and rig capability.
Simulations indicate that if drilling
had been continued, it was likely
that a TD of ± 44,000 ft would have
been possible where it would’ve
been limited by the top drive capability, assuming the ECD-induced
lost circulation rate was still within
the acceptable range.
• Increased focus on ECD management. Previous wells have all been
torque-limited. TD was forced on
when ECD induced losses are intolerable or ROP too low. ECD management included reliance of hole
enlargement with the mud system,
tapered drillstring design with a section of slim-OD drill pipes and thin
rheology mud.
• Emphasis was put on the quality
well path to minimize unnecessary
doglegs for improved torque and
drag.
CONCLUSIONS
The BD-04A well has pushed the
industry extended-reach drilling
envelope for shallow wells to new
heights with fit-for-purpose design
and appropriate practices.
• The use of RSS in the continuous
build top-hole sections, resulting in
a smooth catenary wellbore curve,
which helped to push the ERD limits.
Torque was the limiting factor in
determining the well’s reach. ECD
Based on the drilling torque friction
This plot shows BD-04A’s calculated ECD loads with management was integral to the
factors encountered in BD-04A, TD
overall torque management, and
sensitivity analysis on open-hole size and observed
would have been torque-limited to
the use of mud lubricant was neceslost-circulation
rate
.
+/- 30,000 ft with the original equipsary to reduce the friction factor to
ment of 5-in. drill pipe with API tool
As such, MOQ’s equipment upgrades
a manageable level for the LSND
joints and possibly even less, as the
were directly responsible for at least +/water-based mud system. ECD loads are
ECDs would have been higher, result10,000 ft of additional reach.
higher with increasing reach, and it was
ing in intolerable lost-circulation rates.
D R I L L I N G CONTRACTOR
Reprint DC (Drilling Contractor) © July/August 2009
July/August 2009
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I N N OVAT I N G W H I L E D R I L L I N G
amplified with the shallow TVD of
Al-Shaheen reservoirs. If ECD loads
were not managed, intolerable lost
circulation rates would have led to
the replacement of drilling fluid containing lubricant to seawater, pushing the friction factor higher, hence
reaching the torque limit long before
planned TD.
buckling management and making
connections to avoid stuck pipe or
self-inflicted damage to the wellbore.
5. Hole condition monitoring. Realtime monitoring of torque and drag
and ECD trends and comparison
with the theoretical trends enables
identification of potential problems
and timely corrective actions. Hole
condition monitoring was also
used to project the torque and drag
and ECD loads to TD based on the
actual drilling condition.
A systems approach was required
for a balanced engineered solution.
Extensive torque and drag, ECD
and hydraulics modeling work were
done to identify the bottlenecks. A
gap analysis was performed and a
performance improvement plan produced and implemented, contributing the following:
Fine-tuning of drilling parameters
and drillstring design were made to
ensure TD of the well was reached
within the equipment limitation. It
was also used for ROP optimization. WOB was limited by buckling
of the 4-in. drill pipe, a “maximum
allowable WOB” roadmap was
generated based on the actual drilling condition, and optimum WOB
within the buckling limit was used
to maximize ROP.
1. Knowing what are limiting factors
to pushing the operating envelope
further. Torque and drag review of
offset wells indicated torque was
not limited by the top drive but
by the connection of the 5-in. drill
BD-04A’s measured standpipe pressure and actual
pipe. With the use of up to 10,000 ft
flow rate plot.
of 5-in. drill pipe with high-torque
connection, the torque limit was
Previous wells were torque-limited, with
increased from 32,000 ft-lbs (connection
6. The spin-off benefits from this
TD usually forced on once torque loads
limited) to the top drive limit of 40,000
record well have been extended and
became unacceptable. ECD manageft-lbs.
implemented across the board on all
ment included use of the 5-in. by 4-in.
wells drilled, resulting in ROP improvetapered drillstring and thinner rheology
2. Fit-for-purpose drillstring design.
ment, torque and drag mitigation, ECD
fluids.
Torque and drag modeling indicated that
management, extending the reach of
BD-04A torque was sensitive to the side
Model showed that ECD loads were very
sandstone Nahr Umr wells and drilling
loads in the horizontal section. Lighter
sensitive to hole size and mud rheology.
multilaterals.
drill pipe will generate less side loads,
4. Training and practices. The margin
hence less torque. A tapered drillstring
SPE/IADC 119506, “How Continuous
of error for BD-04A was very narrow.
Improvement Lead to the Longest Horizontal
design with a section of lighter-weight
Well in the World,” was presented at the 2009
The hole cleaning and tripping behavior
4-in. 14-ppf drill pipe placed above the
SPE/IADC Drilling Conference & Exhibition,
are a step-change from conventional
BHA can effectively reduce torque.
17-19 March 2009, Amsterdam, Netherlands.
wells. Extended-reach drilling operation
3. Focus on ECD management. This
practices training are key to familiarize
Article glossary, references, acknowledgeis a critical priority, given that mud
operations personnel with the appropriments and additional graphics are available
is necessary for torque management.
online at www.drillingcontractor.org.
ate practices for drilling, tripping, pipe
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July/August 2009
D R I L L I N G CONTRACTOR
Reprint DC (Drilling Contractor) © July/August 2009