DRILLING WITH CASING

TUBULAR TECHNOLOGY AND SERVICES

DWCTM

OVERVIEWCasing drilling permits operators to simultaneously drill, case and eval-

uate oil and gas wells, thereby significantly reducing drilling time and the

potential for unscheduled events.

Field studies have shown a 20-30% reduction in the time required to drill

wells from spud to rig release when utilizing drilling with casing; and

drilling with casing has demonstrated improved reservoir productivity.

Initially, drilling with casing used traditional casing connections, but

these off-the-shelf connections exhibited performance problems because of

cyclic-torsion loads, sealing capability to overcome dramatic cyclic loads

and significant fatigue.

Grant Prideco, the North American leader in the development of premi-

um tubulars and connections, was faced with a technical challenge — to

design and develop a special connection for casing drilling applications

that would provide:

• Sound economics;

• high resistance to cyclic torsional loads;

• superior sealing capability while subjected to dramatic cyclic loads;

• enhanced fatigue resistance; and

• field-friendly running procedures.

There are a number of casing connections in the market that provide

two, three and sometimes even four of these characteristics. Grant

Prideco's drilling with casing coupled (DWC/C™) connection was devel-

oped to meet all five of the requirements dictated by the new emerging

marketplace.

The DWC™ technology is a family of semi-premium connections

designed for the rigorous conditions seen with casing drilling technology.

FIELD USE/HISTORYThe DWC/C connection can be used with different types of casing

drilling practices including a top drive or a kelly and rotary table.

The connection has been used to drill entire wells, ranging from 2,000 to

8,400 feet of drilling depth in areas such as the Greater Green River Basin

in Southern Wyoming and in the Lobo Trend in South Texas.

US Patent 6,406,070 B1

DWC/C™ RATINGS AND FEATURES

PIN-TO-PIN INTERNAL TORQUE SHOULDER•Mill-end pin made up to a position makeup

mark;•Field-end pin made up to a makeup

torque;•Positive stop controls position offield-end pin;•Tight tolerances for torqueshoulder control; and•Adds preload into the shoulderfor fatigue resistance.

STRESS REDUCTIONGROOVE

• Patented stress reduction groovereduces the stresses in the coupling to

enhance fatigue life;• Allows pin noses to shoulder without a long pin

nose addition;• Allows for a shorter coupling compared to API BTC.

API BUTTRESS THREAD FORM• Widely accepted thread form;• Easily run;• Widely accepted pressure resistance;• Thread sealing obtained with any API connection

thread compound.

OPTIONAL TEFLON® SEAL RING• All DWC models are offered with an optional

seal ring groove;• Seal provided by entrapped seal ring;• Provides a reliable seal for the life of the string,

unlike the thread seal which relies on solids in thethread compound to provide the seal-

ing mechanism;• Seal ring modification

does not affect the con-nection's tensile rating.

AVAILABLE SIZES• The DWC/C con-nection comes insizes from 3 1/2 in to13 3/8 in.

MODELS DWC/C™ and DWC/C-SR™ are the most common models of the DWC

design family and are the recommended connection for most or all of the

casing strings in typical casing drilling applications. The DWC/C engi-

neered design incorporates a torque-shouldering system developed specif-

ically for the torque and fatigue requirements associated with casing

drilling operations. The special coupling element of the torquing system

includes a patented Stress Reduction Groove in the center of the coupling

that enhances the coupling's resistance to cyclic loading typically generat-

ed during casing drilling operations. The DWC/C is also the most eco-

nomical model of DWC offered for casing drilling applications. The cou-

pling turned ODs are the same as for API connections.

DWC/DS™ and DWC/DS-SR™ were engineered for applications

needing more stability in the bottom hole assembly region of the casing

string or to add weight on bit, or both.

The DWC/DS is designed with torque shoulders at both the pin nose and

the coupling face. This system increases the torque strength and improves

the stress concentration of the connections, which improves the DWC/DS

resistance to fatigue loading.

The number of joints needed depends on the application but the

DWC/DS has historically been used in 10 to 12 joint assemblies on the

bottom of the casing string. The typical method used to make these psue-

do drill collars is to use a heavy wall casing that has an OD similar to the

coupling OD of the DWC/C size being used, which is typically the next

casing OD size. For instance, 7-in DWC/C casing could use 7 5/8-in pipe

for the DWC/DS without the need of a crossover. The 7 5/8-in pipe may

be selected so that the ID is very similar to the 7-in casing.

DWC/U™ and DWC/U-SR™ were designed so that the DWC connec-

tion design can be machined on upset pipe, eliminating the coupling.

This integral connection is upset on one end for the box. The pin is

threaded on plain-end pipe.

DWC/U

DWC/DS

DWC/C

MAKEUP PROCEDURES

MILL END

The mill end of DWC/C couplings is made to a position mark placed

on both the mill-end side of the coupling and the mill-end pin. This

precise makeup monitors not only the location of the coupling in the

axial direction, but also the rotational position of the coupling. This is

done to assure a very accurate mill-end pin position in order to obtain a

proper field-end makeup.

FIELD END

The field-end makeup

of DWC/C is very simi-

lar to a connection that

has a torque shoulder.

With the mill-end pin

accurately positioned,

the field-end pin nose

shoulders against the

mill-end pin nose in the

center of the coupling to

a specified makeup

torque. When running a

torque-turn system, the

graph will be very simi-

lar to a premium con-

nection. This eliminates

the need to monitor a

makeup mark on loca-

tion.

SHOULDER

TURNS

SHOU

LDER

TORQ

UE

Max 5200

Max 3314

Ref 20

5.00

0

Applied Torque = 5243 Top Turns = 2.738Shoulder Torque = 3314 Shoulder Tns = 2.629Delta Turns = 0.109 Delta Torque = 1929 Top Delta Rate = 17697

TYPICAL FIELD-END MAKEUP GRAPH(ft

-lbs)

TESTINGWith the introduction of fatigue requirements on a casing connection,

fatigue-life criteria had to be developed. An acceptable fatigue life at dif-

ferent stress levels was obtained to establish a target for testing. A stress

vs. number of cycles curve (S-N curve) was used to define the design win-

dow.

Once a design envelope was developed, the DWC design criteria was

validated by the use of Finite Element Analysis (FEA) and physical testing.

FINITE ELEMENT ANALYSIS (FEA)

Finite Element Analysis (FEA) was performed on

4 1/2 in-OD, 11.60 lb/ft, J-55 DWC/C to verify the

fatigue resistance of the connection.

The connection geometry was meshed to create the

computer model used in the FEA. Pure axial tension

was applied to the ends of the model for mean stress

and ramped up in steps to the final load. The maxi-

mum principle stresses for the nodes in the thread root

radii and the maximum stress points were used to

determine the stress concentration factor (SCF).

The SCF was calculated for every nodal point along

every pin and box root radius for each load step. The

maximum SCF was found in the pin imperfect thread

area, where a fatigue failure would be expected.

TORQUE-TO-FAILURE

Torque-to-failure testing was also conducted on the

DWC/C and DWC/U connections to verify the tor-

sional limits of the con-

nection. The connections

were made up per the

makeup procedure and

then torque was applied

until significant yielding

was visible on the torque-

turn graph. The yield

torque values were com-

pared to the theoretical

yield values.

Shou

lder

Max 15000

5790 Yield Torque

0.50

0

Applied Torque = 11081 Top Turns = 0.340Yield Torque = 5790 Yield Tns = 0.079Delta Turns = 0.261 Delta Torque = 5291 Top Delta Rate = 20272

TORQUE-TO-FAILURE

TORQ

UE

TURNS

(ft-lb

s)

PHYSICAL FATIGUE TESTING

Physical fatigue testing was con-

ducted on 4 1/2-in, 11.60 ppf, J-55,

DWC/C and DWC/U connections.

All of the fatigue samples were tested

to sample failure resulting is a fatigue

crack or an empirical infinite life.

The fatigue testing was conducted

using two different types of fatigue

machines, a rotary, four-point fatigue

machine and a resonant fatigue

machine.

The rotary, four-point fatigue

machine has a more constant bending

moment but is very slow because the

pipe rotates during testing at a few

hundred RPM. The resonant fatigue

machine induces a vibration on the

sample to obtain similar loads as the

other fatigue machine but operates at

a much faster pace, approximately 24-

28 Hz. This reduces the testing time

from days to hours. Similar results

were obtained from both of the testing

apparatuses.

All fatigue cracks were in the pin-

critical area or on the pipe body at a

field induced stress point away from

the connection (e.g. tong marks). The

physical testing correlates with the

findings of the FEA.

DWC/C Fatigue Test Pin Failure

MOTOR MOTOR

ROLLERS

CYLINDER

EXTENSIOMETER

0°

0°

0°

0°

ROTATABLEECCENTRIC

MASS

ROTARY,FOUR-POINT

FATIGUEMACHINE

RESONANTFATIGUEMACHINE

www.grantprideco.com/dwc

TUBULAR TECHNOLOGY AND SERVICES

CORPORATE OFFICE

Grant Prideco, Inc.1330 Post Oak Blvd., Suite 2700Houston, Texas 77056 USA832.681.8000

Tubular Technology and Services1450 Lake Robbins Drive, Suite 500 The Woodlands, Texas 77380 USA281.297.8625 Fax: 281.297.8925

DWCTM

Grant Prideco has produced this brochure for general information only and it is not intended for design purposes.Although every effort has been made to maintain the accuracy and reliability of its contents, Grant Prideco in noway assumes responsibility of liability for any loss, damage or injury resulting from the use of information and dataherein. All applications for the material described are at the user's risk and are the user's responsibility.

Grant Prideco is a registered trademark of Grant Prideco, L.P.

DWC, DWC/C, DWC/C-SR, DWC/DS, DWC/DS-SR, DWC/U and DWC/U-SR are trademarks of GrantPrideco, L.P.

TEFLON is a registered trademark of DuPont de Nemours and Company, Inc.

© 2003 Grant Prideco. All rights reserved.TTS-DWC-10.03-5M-FMC