This document discusses the growing acceptance and capabilities of drilling with casing technology. It provides details on: - Drilling with casing can address issues like stability, lost circulation, and fluids control by keeping casing in the hole at all times. - It saves time by drilling and running casing simultaneously, avoiding trips in and out of the hole. This can result in substantial savings. - Advances in metallurgy and equipment have expanded its use in more challenging applications like offshore drilling of directional wells over 5,000 feet. - Successful projects by companies like ConocoPhillips demonstrated its benefits for reducing non-productive time and costs.

1. Drilling With Casing
Gains Industry Acceptance
While the concept of drilling a well with casing–eliminating the need to drill with one string of pipe and then
replace it with another–is not new, it is an idea whose time has come. The drilling with casing market remains a
comparatively small part of global drilling activity, but advances in metallurgy, equipment and experience are
combining to expand the capabilities of drilling with casing, experts say. And when used in the right situations,
the technology is proving itself in both on- and offshore applications.
Drilling while casing the well bore addresses issues such as stability, lost circulation, fluids control and the need to
bridge troublesome zones, cite those with expertise in the technology. “Drilling with casing is part of a drilling haz-
ard mitigation solution,” asserts Steve Rosenberg, U.S. region product line manager, drilling with casing, for
Weatherford International. “It is a way to get past a problem.”
What Rosenberg and other experts in the field also talk about are the important side benefits from drilling
with casing, including the time saved because the rig is drilling at the same time casing is being run in the hole.
Doing that, according to Bill Lesso, mechanics adviser for Drilling & Measurements with Schlumberger, gives
drilling contractors the ability to save “three flavors of time.” As he describes it, “The three ‘flavors’ we are sav-
ing are the trip out of and back into the hole, a bit of improvement in drilling efficiency, and a reduction of non-
productive time.”
This can add substantial savings on land or offshore, which aggregate in high-cost drilling environments and
during periods of high commodity prices, Lesso emphasizes.
Unexpected drilling hazards and operational issues result in nonproductive time, which an industry consensus es-
timates can run as much as a quarter of many drilling projects, with about half that figure directly related to drilling
troubles that can be directly mitigated with casing drilling, according to John Boyle, vice president CASING
DRILLING®, for Tesco Corporation. He says, “The majority of nonproductive time in any drilling operation comes
when you are tripping pipe. That is when most well control problems show up and when well bore stability issues
really become evident. If you can avoid tripping pipe, you can sidestep much of the typical nonproductive time.”
By Michael Kardos
Special Correspondent
Reproduced for Schlumberger with permission from The American Oil & Gas Reporter
The “Better Business” Publication Serving the Exploration / Drilling / Production Industry
APRIL 2008

2. Benefits Of Drilling With Casing
Rosenberg says Weatherford has used
drilling with casing technology on more
than 800 projects. TESCO’s Boyle re-
ports it has used its systems in almost
1,000 intervals, including more than 350
complete wells.
Schlumberger’s directional solution for
casing while drilling combines its straight
motors, measurement-while-drilling sys-
tem and rotary steerable system to steer
the bottom-hole assembly, and Lesso says
the company has worked with TESCO on
projects with ConocoPhillips to prove the
technology mitigates drilling hazards.
Along with the specialized tools and serv-
ices specific to casing drilling, TESCO
provides tubular services as well as top
drive drilling systems.
Weatherford produces a line of tools
that allows for the casing to remain in
place. Once the casing-drilled portion of
the well bore is complete, Rosenberg says
the casing drill bit is drilled out, left in
the hole, and drilling continues.
Eachsystemoffersstrengthsandweak-
nesses compared with others.
All three industry veterans agree that
drilling with casing can be more efficient,
and therefore faster, than drilling with a tra-
ditional drill stem. Part of that efficiency
may come from the fact the technology
tends to be used in softer formations such
as shales, or formations that have become
depleted as a result of production.
Casing drilling often results in a more
stable well bore, according to TESCO’s
Boyle, who points out that because cas-
ing stays in the hole at all times, every
inch of hole drilled can be kept, even if
stability or well control problems force
the casing to be set and cemented prior
to the full interval being drilled.
One characteristic of drilling with cas-
ing is commonly referred to as the “plas-
tering” or “smear” effect. According to
the descriptions, the proximity of the cas-
ing to the well bore face “mixes” the cut-
tings and drilling fluids to a consistency
that mechanically alters, and thus seals,
the annular ring.
While the smear effect is a delightful
byproduct of casing drilling, Rosenberg
reflects, it also can be vexing because it
does not occur all the time and can be un-
predictable. “Because you have a smaller
well bore annulus when drilling with cas-
ing versus that of conventional drill pipe,
we think the casing is plastering or smear-
ing those cuttings against the wall of the
formation, creating an impermeable bar-
rier.Typically,cuttingsaregroundfiner,and
10-20 percent less cuttings are circulated
to the surface,” he observes.
To underscore the issue, Lesso insists,
“If it wasn’t for the smear effect, I would
not be involved with drilling with casing.
I have spent 25 years trying to solve var-
ious drilling mechanics problems such
as lost circulation, kicks, high torque, vi-
brations, and things of that nature. Lost
circulation and well bore stability issues
are some of the hardest to deal with. Then
along comes this game changer, which
has the potential to solve these problems.”
However, Lesso also acknowledges
that for the skeptical operator, this bene-
fit “requires a leap of faith. As far as I
know,thereisnohardresearchorevidence
as to exactly what the plaster effect is.”
Different Approaches
WeatherfordandTESCO–thetwomain
providers of the technology–offer differ-
ent approaches to help drillers get the bit
to total depth.
In the broadest terms, Rosenberg says,
Weatherford developed a system where-
by casing can be drilled with a propri-
etary casing bit and cemented in place.
The casing bit can be easily drilled
through with a conventional drill bit be-
cause, with the exception of precisely lo-
cated cutting features, the drill shoe core
is made of drillable aluminum.
On the other hand, the TESCO sys-
tem can unlatch, and utilizing a wireline
system, retrieve the drill bit, bottom-hole
assembly and steerable motors or rotary
steerable systems that make directional
casing while drilling possible, according
to Boyle. The bottom-hole assembly then
can be re-run, allowing drilling to con-
tinue, he notes.
TESCOandSchlumbergerhaveteamed
on both onshore and offshore projects to
drill directional sections more than 5,000
feet in length.
Weatherford’s nonretrievable system is
less expensive and simpler to operate in
certain applications than a TESCO system,
both competitors agree. Weatherford’s
drilling with casing systems are not steer-
able, but, “With the stiffness of our system,
you can maintain the tangential angle over
several hundred feet,” Rosenberg attests,
noting thatWeatherford did a job for an op-
eratorintheGulfofMexico,whereitmain-
tained a 70-degree angle for more than 500
feet.
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Casing drilling received a big boost from ConocoPhillips’ drilling in the the mature
Lobo Field in South Texas in 2001. In the past five years, Tesco Corp. reports, its world-
wide drilling with casing footage has increased nearly fivefold.
◆ Improve bore hole stability with less
mechanical damage
◆ Reduce lost circulation even at high ECDs
◆ Reduce trouble time
◆ Eliminate casing strings
◆ Improve well control
◆ Drilling time savings
◆ Improve hole conditioning and production
◆ Improve personnel safety
◆ Reduce rig requirements
◆ Enable more difficult wells
Benefits Of Drilling With Casing
SpecialReport: Drilling Technology

3. There are other differences between
their companies’systems, Rosenberg and
Boyle agree. And the energy services in-
dustry has a number of manufacturers
and suppliers of specialized equipment
for drilling with casing–both surface and
downhole–such as top drives, split blocks,
bottom-hole assembles, torque collars,
steerable motors, drill bits, under-reamers,
and other equipment.
Up To The Challenge
Casing drilling received a big boost in
2001 when ConocoPhillips asked TESCO
to put the technology to work on the com-
pany’sLoboFieldinSouthTexas.Although
this maturing natural gas reservoir still had
strong reserves, both structural and strati-
graphic complications stood in the way of
further production.
As Schlumberger’s Lesso explains,
“Lobo proved the current generation of
retrievable casing drilling.”
Those wells consisted of 95
/8-inch di-
ameter casing drilled to about 2,000 feet,
7-inch diameter casing drilled to between
6,000 and 7,000 feet, and 51
/2-inch diam-
eter casing down to 10,000 feet and oc-
casionally deeper. “Those sections were
long enough that they needed multiple
bit runs and thus a retrievable system.
The Lobo formation is pretty tough and
abrasive,” Lesso comments.
Boyle figures TESCO has completed
more than 200 wells in the Lobo Field.
He mentions another TESCO project,
the Stratton Field, also in South Texas.
There, conventional drill-pipe drilling
had yielded poor results in an aging de-
velopment and marked the Stratton as un-
economical. Boyle says TESCO drilled
57 wells, using casing drilling in trouble-
some zones. The wells often were drilled
in half the time of conventional wells in
earlier efforts, and doubled both produc-
tion rates and ultimate recoverable re-
serves, he reports.
“We don’t trip. We drill it; the casing
is there.You pull the bottom-hole assem-
bly, pump cement, and you are good,”
Boyle describes.
He adds that TESCO has drilled more
than 2.7 million feet of hole with casing
for more than 40 operator clients around
the world. He notes that in the almost
1,000 hole sections TESCO has drilled
with casing, it has experienced no signif-
icant well control incidents and lost no
well bores.
Going Offshore
One of the first instances of drilling
with casing offshore came in the early
part of this century when UnocalThailand
experienced trouble re-entering the top
1,000 feet of hole in about 20 percent of
its offshore wells. A Weatherford unit,
Brit Bit, was part of the early work that
proved casing drilling’s success offshore.
As casing while drilling work pro-
gressed in ConocoPhillips’ Lobo Field,
Lesso says the company became inter-
ested in using the technique offshore.
Following a successful test by TESCO
in 2005, in January 2007, ConocoPhillips
completed what is believed to be the first
well that “drilled directionally with cas-
ing using retrievable bottom-hole assem-
blies from an offshore location,” accord-
ing to an abstract of a case history that
Lesso and others from ConocoPhillips
and Schlumberger presented at the 2008
International Association of Drilling
Contractors/Society of Petroleum Engi-
neers Drilling Conference in March.
The project was conducted on an
Eldfisk well in the North Sea, and con-
sisted of drilling 10,968 feet of the well’s
total 13,600 feet directionally with cas-
ing, Lesso reveals. He says one string of
Completed in January 2007, a ConocoPhillips’ well at the Eldfisk Bravo Field in the
North Sea is believed to have been the first offshore well drilled directionally with cas-
ing using retrievable bottom-hole assemblies.
Drill Lock Assembly (DLA)‡
connecting BHA to
Casing Profile Nipple‡Internal
tandem
stabilizer‡
PowerPak†
straight PDM
Vibration
sensor sub
Roller
reamer
Casing shoe‡
Motor bit box
Under-reamer‡
Pulse† telemetry and
surveying MWD system
PowerDrive X5† RSS
PDC bit
One of the key steps in the development
of casing while drilling systems was the
ability to drill directionally with the tech-
nology. Shown here are the various com-
ponents in a directional casing while
drilling bottom-hole assembly similar to
those TESCO and Schlumberger have
used both on- and offshore to drill direc-
tional sections more than 5,000 feet in
length.
SpecialReport: Drilling Technology

4. 103
/4-inch casing and one string of 73
/4-
inch casing were used, with well path in-
clinations up to 60 degrees.
Rosenberg offers, “One of the big ben-
efits in taking casing while drilling off-
shore is that cost savings are magnified
compared with onshore. For example, a
jackup rig may charge $100,000 a day
and a deepwater floating rig may work
for $500,000 a day. We think the prize
for drilling with casing is in deep water
because day rates are so high.”
Lesso adds, “It is no longer a matter
of whether operators will want to do this
offshore, but when.”
However, Rosenberg tempers the en-
thusiasm for offshore applications by
cautioning, “The problem offshore comes
about because the wellhead is on the sea-
floor,andyouhavetodrill-inthecasing and
simultaneously land it on the wellhead,
so there are spacing considerations to
take into account.”
Technology Advances
Advances in science and technology
give oil and natural gas drillers better,
more reliable equipment with which to
undertake drilling with casing.
“The metallurgy in 1950 was marked-
ly different than it is today,” Lesso points
out. “When the drilling string is casing,
by definition it is not as strong.”
He notes standard 5-inch drill pipe can
endure 25,000 foot-pounds of torque, and
some 57
/8-inch drill pipe can handle as
much as 55,000-60,000 foot-pounds.
Standard 95
/8-inch casing can handle only
14,000 foot-pounds of torque, Lesso con-
cedes.
Now, however, “There is special 95
/8-
inchcasingthatcantakemorethan100,000
foot-pounds of torque,” he reports.
The development of casing collars and
torque rings gives casing joint shoulders
greater strength to carry higher torque
loads, Lesso explains. Greater strength
translates to a greater lateral reach in a
directional well, he adds.
“We have gone out 5,000 feet on an
offshore, directional well,” Lesso reveals.
“These new casing strings give us the
ability to plan directional projects off-
shore with casing that have reaches ex-
tending as much as 10,000 feet.”
Being able to simultaneously drill
with casing and steer in an offshore en-
vironment is where the cost savings and
benefits are most apparent. “We think the
prize for drilling with casing is in deep
water because the magnitude of day rate
costs is so high,” Rosenberg comments,
adding that the potential for reserves off-
shore to be much greater than onshore
compounds the economic benefit.
Strides also are being made on equip-
ment at the bottom-hole cutting face.
Rosenberg explains that Weatherford’s
line of specialized bits is designed for in-
creasingly hostile environments. He says
the initial bit, developed in 1999, is suit-
ed for soft formations with less than 3,000
psi of combined compressive strength
Improved metallurgy along with
casing collars has resulted in a
special 95
/8-inch casing able to
endure more than 100,000 foot-
pounds of torque, surpassing
even the strength of 57
/8-inch
drill pipe.
The casing while drilling sur-
face equipment on this well in-
cluded a casing drive system,
a split block, a swivel with
space for the wireline BOP, a
top drive system, and 103
/4-
inch casing.

5. (CCS). The second bit can handle 7,000
psi of CCS and has a cutting surface im-
pregnated with 6-millimeter, thermally
stable polycrystalline diamonds. A third
casing drill bit has a cutting structure con-
sisting of 13-19 millimeter polycrys-
talline diamond compact cutters, and can
handle up to 15,000 psi of CCS, he adds.
To give the latter bit drill-out capabil-
ity, Rosenberg says pressure actuation
extends the PDC cutting blades to the an-
nulus, allowing the casing drill bit to be
drilled out conventionally.
At TESCO, Boyle adds, “The neat
thing that has happened over the past 12-
14 months is our ability to attach anyone’s
rotary steerable system to the bottom of
our bottom-hole assembly, (enabling
them to) steer the casing.”
He acknowledges that in any casing
drilling application, there are limitations
on build rate, fatigue strength and other
issues associated with the properties of
the casing string, “but still this opens a
lot of possibilities.”
Rig Modifications
One concern drilling companies have
expressed about drilling with casing is
the potential need to modify their rigs.
“There are certain basic modifications
that need to take place,” Boyle allows.
Some of those changes include top
drives, and in some instances a split-
block assembly that allows wireline to
be used in running and retrieving the bot-
tom-hole assembly. But Boyle points out
that most new rigs that have come on the
market in the past few years are built so
as to easily accommodate any changes.
Rosenberg says Weatherford’s ce-
ment-in-place system is relatively sim-
ple to operate and requires no rig modi-
fications. “We can rig up our drive system
on virtually any rig with a masthead
height of 65-70 feet, and drill the casing
in,” he states, estimating that fewer than
5 percent of the drilling rigs working in
North America would not be suitable for
the system.
Even a super single rig can generally
handle the top drive system and a standard
40-foot joint of casing, Rosenberg says.
One important difference between the
Weatherford and TESCO systems comes
in the area of logging and data collection.
Rosenberg says Weatherford’s nonre-
trievable system offers only limited log-
ging options, while Boyle notes that
TESCO’s wireline retrieval configura-
tion makes logging possible.
All three men say they expect the mar-
ket for casing while drilling to grow be-
cause downhole conditions are becom-
ing more difficult and high commodity
prices make those assets worth pursuing.
Boyle attests, “The casing while drilling
market is starting to pick up quite a bit of
speed. Shell, for instance, is a firm believer
in the technology. Hess, ExxonMobil and
ConocoPhillips, which is one of our largest
supporters, are trying it, as are Petrobras
and others. Saudi Aramco, Occidental
Petroleum and many independents also
have expressed interest in casing drilling
with TESCO.” ❒
SpecialReport: Drilling Technology