Technical limit thinking produces steep learning curve - Shell

Technical limit thinking produces
steep learning curve
Daysto drill a well went from almost 100to below 60 daysin Saih Rawl.
OlutayoAjimoko,Petroleum Development Oman*
Technical limit thinking is a conceptual feedback tool for
maximizing drilling efficiency.It involvesfirst determining the
conditions and engineering practicesthat willlead to the minimum
time and/or cost at which a given well can be drilled,
and then employing motivational and training techniques to
implement those practices. Shell and Petroleum Development
Oman (PDO) produced a highly developed technical limit
program for the challenging Saih Rawl gas field, which culminated
in the landmark drilling of the field'sfirst sub-60-day
well, Saih Raw1228, in 57.89 days, against an AFE time of75
days. Shell and PDO leveraged the methodology to further
teamwork, knowledge management and bit optimization to
progressivelyreduce well construction time.
BACKGROUND
Saih Rawl is an onshore deep gas field in southern Oman
and the biggest gas field in the country. It is split into three
geographically and tectonically separated blocks: SR Main to
the north, SR Graben and SR South, Fig. 1.
The field is a large, elongated northeast-southwest-oriented
anticline, with the anticlinal axisdipping to the southwest. A
system of northwest-southeast-trending faults delineates and
sealsthe structure's northern boundary. The varying compartmentalization
of the fault system accounts for the high anisotropy,
and thus for the extreme drilling challengesencountered
in the different lithological packages.
A typical well design in the Saih Rawl field starts with a
I7Y2-in. hole from surface to the Naith limestone at about
950 m (3,100 ft) to set 133h-in.casing.This is followed by a
I2IA-in. section to about 3,200 m (10,500 ft), where the 9%in.
casing is set in the AI KhlatalHasira formation. Thereafter,
a 2,050-m (6,730-ft), 83h-in.section is drilled to section TO
in the Amin formation. The I7Y2-in.section and I2IA-in.section
are drilled on rotary.
At the beginning of field exploration in 1991 and of exploration
on surrounding wells, the 83h-in. section was initially
drilled with roller-cone bits on rotary assemblies.In the intervening
time, roller-cone bits have been gradually replaced by
diamond-impregnated bits, so that by 2005, the entire 83h-in.
section from drillout to TO was drilled almost exclusivelywith
turbine drive systemsand diamond-impregnated bits.
TECHNICAL LIMIT WELL
The technical limit is defined as a measure of perfect performance
limited only by technology availableand/or by the
'Since writing this article, Mr. Ajimoko has changed employment. He now
works for BP.
DRILLING TECHNOLOGY
laws of physics. In well drilling, this performance measure is
the minimum possible time and/or cost to drill a typical well
in a given field. In Saih Rawl, lessonslearned in previouswells
helped the team to identify the optimization practices that
would lead to a technical-limit well, Fig. 2. Among these:
· A Le Fleur circulation packer could be used, and downtime
could be minimized to reduce the flat spot berween the
I7Y2-and 12IA-in.sections.
· A higher-capacity centrifuge could optimize hydraulics
to speed up the 8%-in. section. · A wireline formation tester could be run to eliminate
three logging trips and a wiper trip.
In addition, the technical limit well would maximize trip
efficiencies,optimize hole cleaningand mud conditioning and
increasebit life.The team determined the Saih Rawl technical
limit well time to be 32.7 days.
Removingtechnologicallimitations from the equation yields
the "perfectwell time," a theoretical construct that can be useful
for defining drilling targets. The perfect well time is the
minimum time in which a well could be drilled limited only
by the physics of the drilling practice, calculated from clearly
definedphysicalfactorsthat constrain the drilling time: the rock
strength, operational limits, number of casingstrings,hole size,
etc.The perfectwell time in Saih Rawlis 18.4 days,Fig.3.
WELL CONSTRUCTION
Historically, about 70% of the total well construction time
in Saih Rawl, as in most deep gas wells, is spent drilling ahead
and tripping. The bit penetration rate and bit life, therefore,
both have a major impact on well construction time and cost.
Hypothetically, if both penetration rate and bit life could be
doubled, an average 30% total reduction in drilling time and
cost would result.
A dynamic drilling optimization process has evolved for drilling
the Saih Rawl field. The drilling program employed on Saih
Rawl 228 involved drilling the I7Y2-in. tophole section with a
roller-cone bit to a TVD of959 m (3,150 ft) in the Naith-A formation
and casing off with I33h-in. casing. The casing was set
about 15 m (49 ft) into the Naith-A limestone to minimize the
exposure time of the Shargi shales and to reduce casing costs.
Next, rwo PDC bits on rotary drilled the I2IA-in. surface-hole
section to a TVD of 3,049 m (10,000 ft) in the AI Khlata sandstone,
and it was cased off with a 9%-in. casing. It was critical in
this hole section to case off the potentially hydrocarbon-bearing
Shuaiba and Mafraq formations above the AI Khlata, and to isolate
the troublesome and time-dependent Gharif shales.
The 83h-in. section was drilled to a TVD of5,287 m (17,350
ft) in the Amin formation with four diamond-impregnated bits
World Oil JULY 2007 103

DRILLING TECHNOLOGY
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Formation
FiqaArada
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NaithAIB
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.NahrUmr
Shuaiba
Kharab
Lekhwair
Habshan
Tuwaiq
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Mafraq
Sudair
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KhuffM
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GharifL
AIKhlata
Baseincise
valley
188
230
974
1;'237
1,391
1,481
1,546
1,585
1,808
1,933
1,973
2,110
2,182
2,237
2,693
2,879
2,988
3,061
3,110
3,207
SahNihayadal 3,424
Ghudun I 3,564
Barakat
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455
762
2,351
4,370
4,442
4587
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5,348
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5.363
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Fig. 1. A stratigraphic column showing the formation tops
associated with the Saih Rawl gas field.
on turbine. The 83/s-in.section servedasboth the intermediate
and production sections.A tapered completion string of 4\12
x 5 x 5Y2-in. chrome tubular was then run and cemented in
place.The chrome tubular was selectedto mitigate corrosion.
The 83/s-in.section presentsthe greatestchallenge to successfully
drilling useableholes in Saih Raw!, becausethe rock
strength is very high, with unconfined compressivestrength
sometimes on the order of 60,000 psi. In addition, local lithological
variation, compounded by diverse anisotropies, makes
drilling optimization difficult. It follows that this is the most
104 JULY2007WorldOil
E 1,000
.c
c.
CD
"C
~3,000
5,000
SaihRawltechinicallimit
well time=32.7days
Rig days
ITI1)Wheeledloads;2) Nightmoves;3) Sparemudtanksandauxiliaryequipt;
4) Incentivesfor movers.
~ 1)OriIl1~-in. sectionin36hours;2)Optimizeholecleaningandhydraulics.
[[] 1)Minimizedowntime,reduceflatspot;2) EmployLeFleurCirculationpacker.
@]1)OriIl12'4-in.sectionin4 dayswith 1 POCbit,includingwipertrip;
2)Optimizehydraulics;3) UsemodifiedOBM.
[[] 1)Increasetrip efficiency;2)Improveholeandmudconditioning.
[I] 1)Orill83/s-in.sectionin 2 bit runswI infinitelydurableimpregnatedbits.
2) InstallcentrifugewI highercapacityto optimizehydraulics.
II] 1)Runpressuretesterandeliminate3 loggingtrips pluswipertrip.
Fig.2. The drilled depth is plotted againsttime for the
technical limit well, along with practices that would be used to
achieve the limit.
'"
Theperfectwell
(18.4days)
to
C
'"
Ec
'5iTechnicallimit
Q..well(32.7days)
Basecase
well(60.7days)
-----------.
ILaserdrilling(6)I
IIntelligentandautomatedrigsystem(F)I
Liquidcasing/drillingwithcasing(E)I
IIntelligentrockandfluid evaluationlogs(0)I
~
IMaximumvaluedrilling(C)I
I Minimumcostdrilling(B)I
~
IOptimizedrig moves,offlinemaximization(All
Experience
Fig. 3. The performance curve of the perfect well is shown.
crucial hole section, accounting for about half of total well
construction time. Moreover, it penetrates the Miqrat and
Barik objective reservoirs.Drilling the section with diamondimpregnated
bits is a lesson learned following several uneconomic
and failed attempts to drill the section with PDC bits
on rotary and with motors.
CRITICAL SUCCESS FACTORS
Approaching the technical limit requires optimizing all the
factors that enter into the drilling operation. Optimizing the
staff includes both increasing their productivity and encouraging
and using crew members' ideas for optimizing other
factors, such as knowledge management and drillbit performance.
Shell and PDO used these strategies in Saih Rawl to
cut well time by over 40%.
Teamwork. The foundations of any successful team effort
are open, free communication and a shared goal.The rig team
is put on an incentive program at the beginning of the contract,
and the performance incentive goal bonds the rig team
together. The rig team consists of the drilling contractor, the
service vendors and the drilling optimization engineer. The

DRILLING TECHNOLOGY
160
140
120
100
en
~ 80
60
40
20
o
...............
Saih Saih
Rawl Rawl
197 204
Saih Saih Saih
Rawl Rawl Rawl
208 215 221
I
Saih Saih
Rawl Rawl
225 228
Fig. 4. Lessons learned while drilling the Saih Rawl204
well helped operators progressively reduce drilling time to
ultimately achieve a sub-50-day well.
cohesiveness established early in the campaign has sustained
the continuous performance improvement of the rig. The initial
motivation for performance was the reward incentive, but
this was largely superseded by the operational excellence principles
and technical limit philosophies that the drilling office
team incorporated into the modus operandi. The following
key points are worth mentioning:
· Continuity. The rig has maintained most of the crew
members who began the contract in 2003. As a result, rig efficiency
and effectiveness have been excellent.
· Competition. Desire to outperform other rigs in the
field forged a stronger bond between the rig team and the office
team, perhaps overriding the team incentive alone.
· Communication. Goals were clearly communicated and
understood across the team.
· Operational Excellence. OE is a process-oriented enterprise
program that drives improvements in the way a work
group or corporation delivers products and services to its customers.
Operational excellence calls for more than subject
matter expertise and a talented internal team.
The OE philosophy in PD~'s Exploration and Gas department
aims to incorporate the following principles:
Ideas from field staff drive success. The Saih Rawl well
engineering and rig team members are motivated to improve
operations. Team members are respected and their suggestions
are encouraged. A constant feedback and feed-forward cycle
ensures continual improvement.
Analysis paralysis breeds crisis. Rather than focusing on
analyzing potential problems or improvement opportunities,
which may allow them to become much more troublesome
and costly, team members are empowered to make decisions
and solve problems at the lowest possible level. This has minimized
operational failures while drilling in Saih Rawl. Every
team member is empowered to stop work not only for safety,
but also to increase operational excellence.
Ideas need champions. Leadership in the department
aims to encourage originators of ideas to champion them by
spearheading the efforts to develop and implement them.
Team leaders also sometimes discretionally select champions
to serve as focal points, enabling an all-inclusive performance
improvement environment.
Knowledge management. The Saih Rawl experience illustrates
that the time value of knowledge supersedes the time
value of money, especially when drilling for deep gas. The primary
objective of the team's knowledge management strategy
106 JULY 2007 World Oil
--......- - -
-
- -
- -
Fig. 5. The 12V4-in.Hycalog DSX290A2 PDC drillbit.
wasto drill each hole section correctlythe first time. Recycling
of knowledgeand lessonslearned were de-emphasized in favor
of reinforcingpracticesworth replicating or best practices, and
this expedited decision making.
Total Quality Well Delivery(TQWD) was achievedin Saih
Rawl field by adequately managing lessons learned from past
wells and applying them to subsequent wells, Fig. 4. Team
motivation was emphasized over complex logic to achieve
TQWD.
Benchmarking also played an important role. Historically,
three KCA Deutag rigs operated in the field since 2003, and
they all drilled the same well types. Therefore, data exchange,
information sharing and benchmark practices worth replicating
were easilyestablished,and most of the unpleasant lessons
did not have to be learned twice.
Staff continuity also contributed to maintaining a useful
knowledge base. Staffmembers moving up or moving on had
replacements waiting within the crew and being mentored.
This practice and long tenures (at least 2 yr) of the incumbents
have facilitated a downward trend of the performance learning
curve. Extensive lessons were learned on Saih Rawl 204,
which took more than 130 days to drill. The well was especiallyproblematic
due to the difficult directional work carried
out, and the lessonslearned were passed on.
Knowledge management in the Saih Rawl field has had to
be dynamic since 2003, becauseat any point in time there are
at least three rigs drilling different hole sections or performing
different phases of well construction. The drilling team
was given the rare opportunity of simultaneously learningbefore-doing,
learning-while-doing and learning-aFter-doing.
The end result is the progressivedownward trend in learning
curve time.
Bit optimization. The biggestfactor to reduce wellconstruction
cost and time is drilling useable boreholes more quickly.
Bit optimization is a continuously evolving process in Saih
Rawl field. Drilling optimization engineers, supplied by the
vendors who worked in the PD~ officeas part of the rig team,
have sped up bit technological advancement and optimized
the bit-application process.

Fig. 6. The 83fa-in.Smith K507BCTPXX diamond-impregnated
bit.
To date, the biggest improvement has been recorded in the
121,4-in. section with innovative developments in POC bit
technology. The typical formations penetrated in the 121,4-in.
section include shale, sandstone, limestone, clays, dolomites
and sometimes streaks and beds of pyrite, the latter having been
penetrated in the dolomitic limestone of the Khuff formation.
To improve drilling efficiency and meet the challenges
posed by the formation vagaries, the bit design has undergone
several iterations and revisions in cutter size, number of
blades, diamond hardness and bit proflle. The POC bit durability,
stability and aggressiveness also have undergone several
tunings and re-tuning.
The Hycalog OSX290 drillbit has proven to be a game
changer, as the bit has helped reduce construction time in the
121,4-in. section by an average of 41 %, Fig. 5. The bit has a
parr-ring design that ensures total lateral stability and a proprietary
"steering wheel" to ensure good borehole quality.
Notable progress has also been recorded in the 83h-in. section
typically drilled with a diamond-impregnated bit on a
turbine drive. The hole section is very tough due to the uncompromising
mix of lithologies, and reliability is the prime
objective. The Smith K507BCTPXX has proven to be the
most reliable bit from the stock on offer; the choice was
reached after several wells, Fig. 6.
There are two scenarios for performance opportunity in
this section. The first is improving the durability of diamondimpregnated
bits and making them stay in the hole longer.
This strategy gives a longer section interval but at a slower
drilling rate. The second scenario is sacrificing the durability
to achieve faster ROP. The downside to this strategy is that it
will require more bits to drill the section. So far, the second
scenario has given the best result and is the preferred strategy.
The most critical success factor is pulling the bit at the right
time, and this was determined by employing Minimum Specific
Energy (MSE) and Economics Gradient Curves (EGC).
DRilLING THE LIMIT
Technical limit is a means to an end, not an end in itself It
is only a vehicle to stimulate creative thinking and shift paradigms
from the school of "business as usual" and "this is the
way we do it," to a "what if?" or "can do" mentality. If an organization
or business does what it has always done, the same
results will be achieved.
Living the limit raises the bar of operational excellence and
safety by two notches. First, it involves innovative thinking,
employing synergies and taking creative ownership of the results.
Creative ownership of results involves turning failures
into launching pads to future success and perpetually pursuing
business improvements. Implementation of technical limit
thinking in the Saih Rawl has contributed to well cost and
time reduction of over 40% since its implementation. WO
THE AUTHOR
Olutayo Ajimoko worked for Shell E&P as a well
engineer in charge of two heavy land rigs drilling
deep gas in the Saih Rawl field. He provided singlepoint
well engineering, operations and logistics
support to the combined drilling budget. He joined
Petroleum Development Oman as a well delivery
consultant and was actively involved in the implementation
of the technical limit philosophy. He
cross-trained as a production technologist with
extensive deepwater experience working for Star
Deep Water Petroleum Ltd. in Nigeria and the US. Mr. Ajimoko previously
worked for Texaco and Chevron. He is currently employed by BP.
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