World Oil
®
Originally appeared in
JANUARY 2016 issue, pgs 59-62. Posted with permission.
CASING ADVANCES
Development of gas-tight connection for deepwater
drilling and completion operations
The petroleum industry’s
growing need for gas-tight
connections is being driven by
complex wells requiring highpressure completions and
fracturing jobs, or managed
pressure/underbalanced
drilling operations.
ŝŝWENDELL BASSARATH, MARTA
LAFUENTE and ROMAIN BRANLY, Vallourec
Operators exploring in the Gulf of
Mexico are drilling increasingly more
complex wellbore geometries, with additional technological challenges that
combine deepwater environments with
increased hole depths. To safely and efOCTG fitted with VAM Express gas-tight
connections stacked in the yard ready for
deepwater deployment.
ficiently deliver the wellbore requires a
high level of engineering expertise, combined with specialized tools and completion technologies. Tubulars used in these
deepwater operations provide the required high-tensile and torque ratings.
However, mechanical performance is
just a starting point, and other critical criteria must be met to ensure operational efficiency and a safe working environment.
The available OCTG-based connections
and drill pipe risers meet some of today’s
requirements, but operators have challenged the service industry to develop
new gas-tight tubular connections designed specifically for the following applications: 1) high-pressure completions/
fracture stimulations; 2) drill stem testing; 3) managed pressure/underbalanced
applications.
TECHNOLOGY RESPONSE
In response to client requests, Vallourec’s R&D engineering team started
working on a new gas-tight connection
with a metal-to-metal rotary seal. The
engineering process used extensive finite
element analysis (FEA), which produced
a hybridized version of a premium, double-shoulder, gas-tight connection from a
drill pipe riser.
The new connection, called VAM Express-M2M (Fig. 1), provides the highpressure capability of premium casing
connections, coupled with the robustness and increased torsional strength
associated with a double-shoulder rotary connection. Qualification testing
was performed on the critical sizes and
involved standardized make-and-break
testing, and over-torque analysis, in addition to combined loading and fatigue
analysis. In accordance with the company’s commitment to safety, the connection provides one of the industry’s
highest operating margins for a gas-tight
connection and is rated to withstand
30 kpsi, internal pressure, and 25 kpsi,
external pressure. The connection can
be used for both drilling and completion operations, so it can deliver considerable cost savings due to improved
operational efficiency.
DESIGN CRITERIA
The criteria for developing a new gastight connection for deepwater stimulation operations was based on the following requirements:
• Safety. Due to the severity of the
conditions during completion operations, safety was a primary concern.
This would require comprehensive
gas-tight sealing capability to eliminate trapped gas when running the
string.
• Ease of use. To simplify operations
and reduce costs, completion strings
should be run by the same drilling
crew and rig.
• Robustness. Completion strings
are usually run-in on several trips
on one rig and will generally be used
on multiple rigs. These connections
must be strong enough to withstand several runs, which requires
World Oil® / JANUARY 2016 59
CASING ADVANCES
Fig. 1. VAM Express combines highpressure gas-tight capability with the
strength of a double shoulder rotary
connection.
Fig. 4. Seal engagement and make-up process.
Pin
First contact
Box
Fig. 2. Analysis of contact taper/radius
revealed that the interface creates
dispersion of the stress repartition,
increasing the risk of losing sealability
under tension.
Fig. 3. Analysis of contact taper/radius
revealed that the interface allows for
better dispersion of peak stress and is less
sensitive to galling, providing a smooth
contact increase.
resistance to galling, while remaining competent throughout multiple
make-ups and break-downs.
The primary objective for the R&D
60 JANUARY 2016 / WorldOil.com
Pin
Seal radius
engaged
Box
team was to design a connector with a
minimum gas-tight rating of 20,000 psi,
that has similar operational capabilities to
drilling products and is inherently robust
by design. The best way to accomplish
this objective was to base the new gastight connection on field-proven OCTG
connectors with metal-to-metal seals that
have been deployed successfully in the
field for decades. The new joint would
also feature a premium double-shoulder
drilling connection that has demonstrated good mechanical performance and exceptional longevity in field applications.
The main features inherited from the
existing double-shoulder drilling connection include:
• Capable of functioning as a drilling
connector.
• Capable of high torque, up to 100%
more than comparable API connectors provided by the primary and
secondary shoulders, and the proprietary thread design.
• Easy stabbing provided by the optimized taper of the stabbing flank of
the thread profile.
• Quicker make-up and deeper stabbing provided by the connector taper and proprietary thread design.
•Improved fatigue resistance provided by an elliptical thread root design.
• Reduced risk of wedging, due to the
reversed angle on thread crests.
Next, based on historical knowledge
and application expertise, the design team
Pin
Seal + taper
engaged
Box
Pin
Seal + taper +
shoulder
engaged
Box
concluded that the best place to position
the seal was in the non-active cylindrical
part of the pin nose. This section is sufficiently thick to provide stable behavior
through the loading cycles while guaranteeing a gas-tight seal. Once the location
of the seal was selected, additional design
criteria were identified to ensure optimized performance and a safe working
environment, including:
• Ability to resist high gas pressures.
The physical interference between
the pin and the box must generate
sufficient stress to ensure gas-tight
capability.
•Ability to guarantee gas-tight performance throughout the life of the
connector. The seal must always
work in the elastic zone of the material. It must have sufficient contact
surface and contact pressure on the
seal throughout the working life of
the connector.
• Ability to avoid risks of yielding of
the pin nose to avoid a potential
safety hazard when breaking out the
connection (trapped gas). The connector shall avoid geometries with
potential gas-trapping potential.
• Ability to avoid galling. The higher
stress on the seal must be lower than
the material yield strength at all
loading points. The design should
prevent sudden contact pressure increases on the seal.
During the development phase, the
team experimented with a contact taper/
CASING ADVANCES
QUALIFICATION PROCESS
A review of standard drilling practices
and fracturing operations was performed,
using the new VAM gas-tight connection
to assess performance. Preliminary testing was based on calculations using finite
element analysis (FEA), before actual
physical tests were performed. Based on
the above listed evaluations, the qualification program was defined as follows:
• Evaluation of sealability and stress distribution, as well as load test (pressure,
tension, bending and compression).
• Evaluation of fatigue resistance-resonant fatigue bench test.
• Evaluation of torque capacity.
• Evaluation of galling resistance and
pressure after several make-ups and
break-downs.
This intensive qualification program
was intended to confirm expected performances and validate field applicability for
the new connection. All of the qualification tests were performed using calibrated
test devices, and samples were machined/
prepared to reproduce the most critical
configurations.
For each size, the most extreme cases
of tolerances and make-up torque were
chosen to ensure that the critical combinations were tested: 1) The combined
load configurations tested were manufactured with the minimum interference and
contact pressure, which assessed pressure in the critical configuration; 2) The
make-and-break configuration tested was
manufactured with the maximum interference and contact pressure, and therefore assessed the degree of galling in the
critical configuration.
Fig. 5. Good agreement between FEA make-up curve (left) and physical test (right)
documents high torque capabilities.
Total torque, ft/lb
Int. shoulder
Int. seal
Ext. shoulder
Threads
Aimed torque, ft/lb
Shouldering torque line
100,000
90,000
Over-torque L6302 - next generation gas tight 57
Total torque
Calculated MUT
80,000
Makeup torque, ft/lb
70,000
Makeup torque
taper design but dismissed the option,
since this type interface creates a dispersion of stress repartition and is more
sensitive to galling, and increases the risk
of losing sealability under tension, Fig.
2. These factors led designers to use a
contact taper-on-radius design, because
it naturally controls peak stress, allowing for a smooth contact increase on the
seal, making it less sensitive to galling,
Fig. 3.
The final design of the connection
seal includes a soft taper on the pin nose’s
outside diameter and a seat with a large
radius on the box. The taper provides the
connector with a smooth contact increase
during the make-up phase (Fig. 4), and
the seal radius helps distribute stress, thus
reducing the risk of galling.
60,000
50,000
40,000
30,000
20,000
10,000
0
0.0
Rotation
0 = initial position of the meshed geometry
0
1.1
1.2
1.3
1.4
Turns
1.5
1.6
1.7
Fig. 6. Threads on box and pin in good condition after 100 make-ups and break-downs.
TORQUE CAPACITY EVALUATION
The FEA evaluation gave precise
data concerning the connector’s behavior during make-up. After FEA analysis,
the testing was confirmed by physical
tests. Figure 5 shows the make-up curve
comparison between FEA and physical
testing. These tests confirmed the joint’s
torque capacity, up to 100% more than
API, and that over-torque behavior meets
the required specifications.
GALLING RESISTANCE
EVALUATION
FEA verified that the higher stress pressure on the connector was lower than the
material yield strength at all load points,
and the design prevented sudden contact
pressure increases on the seal. This behav-
ior will mitigate the risk of galling on the
seal. The joint’s resistance to yielding and
galling was confirmed by performing 100
actual make-and-breaks, Fig. 6.
GAS-TIGHT EVALUATION
FEA testing confirmed that there is
sufficient contact pressure on the seal at
all loading points of the working envelop
of the connector to achieve the sealing
objectives, and guarantee safety during
operations. The physical load testing was
performed with nitrogen at a third-party
laboratory to guarantee the impartiality of
the results.
The tested envelope corresponded
to 90% of the Von Misses ellipse performance of the gas-tight connection. The
pressure rating achieved during the cycle
World Oil® / JANUARY 2016 61
CASING ADVANCES
cated the new gas-tight joint would provide superior fatigue resistance.
Fig. 7. Test results showed no connector leaks using multiple criteria.
Next generation gas-tight connection 39 loading points tool joint: 5½-in.
OD x 2⅞-in. ID-grade 130 ksi tension + compression + IP bending 15°/100 ft + EP
35,000
The new VAM Express-M2M connection is a cost-effective gas-tight connection
that combines the capabilities of a highpressure drill pipe riser with the robustness of a premium double-shoulder rotary
connection. The combination of features
gives operators and drilling contractors the
flexibility to use the same tubular string for
both drilling and completion operations,
without compromising performance or
safety. The connection is optimized to prevent gas entrapment and provides a high
margin of safety. It also has the ability to
complete multiple fracing jobs without repair, and is easy to fish from a wellbore, due
to its slim-connection design.
4
30,000
25,000
OPERATIONAL BENEFITS
5
3
20,000
2
15,000
Pressure, psi
10,000
5,000
1
0
-5,000
-10,000
7
-15,000
-25,000
-30,000
-35,000
-300,000
Connector 100%
Connector 90%
Loading pass
Loading points
Intrade
Extrade
8
-20,000
9
-200,000
-100,000
0
100,000
200,000
Tension, lb
300,000
400,000
500,000
600,000
700,000
ACKNOWLEDGMENT
This article is derived from IPTC paper 18568, “Development
and Qualification of a Next Generation Gas Tight Connection
Incorporating Metal-to-Metal Technology.” It was originally
presented at the International Petroleum Technology Conference,
Doha, Qatar, Dec. 6–9, 2015.
Fig. 8. Test results showed no connector leaks using multiple criteria.
Next generation gas-tight connection 57 loading points, tool joint: 7⅛-in.
OD x 4⅜-in. ID-grade 122 ksi tension + compression + IP bending 15°/100 ft + EP
30,000
25,000
20,000
WENDELL BASSARATH is a
global product line manager at
Vallourec and manages the
company’s drill pipe portfolio.
He has over 20 years of
industry experience in drilling
operations and new technology
development. He has extensive knowledge of
M/LWD and directional tool development. His
experience also includes several years in R&D
at Halliburton. Prior to joining Vallourec, Mr.
Bassarath was a global product champion at
Weatherford, responsible for commercializing
and deploying the motary steerable system. He
holds a BS degree in engineering physics/
applied physics from the University of the West
Indies, St. Augustine Campus.
4
3
5
2
15,000
Pressure, psi
10,000
5,000
0
1
-5,000
-10,000
7
-15,000
-20,000
6
9
-25,000
-30,000
-600,000
Connector 100%
Connector 90%
Loading pass
Loading points
Intrade
Extrade
8
-400,000
-200,000
0
200,000
was up to 30 kpsi, internal pressure, and
25 kpsi, external pressure, for the smallest
size, and 25 kpsi, internal pressure, and 20
kpsi, external pressure, for the largest size.
To more accurately simulate well conditions and increase test severity, the cycle
included combined internal/external
pressure in tension or compression and
bending up to 15°/100 ft. Figs. 7 and 8.
FATIGUE EVALUATION
An accepted industry fatigue performance standard maintains that a drill pipe
connector should always be stronger than
the welded pipe. To confirm the gas-tight
400,000 600,000
Tension, lb
800,000
1,000,000 1,200,000 1,400,000
connection met this standard, fatigue resistance was verified, using FEA and a stress
concentration factor (SCF) methodology.
SCF tangential located in the critical point
of the connector was compared to the
weakest point of its associated pipe. The
results indicated the connector would have
long fatigue life.
Next, resonant fatigue machines were
used to bench test samples at a frequency
of approximately 28 Hz. All of the samples were filled with water and tested at
one atmosphere, with a constant 200-psi
internal pressure. Axial strain gauges on
the outer diameter of the pipe body indi-
Article copyright © 2016 by Gulf Publishing Company. All rights reserved.
MARTA LAFUENTE is a product
champion at Vallourec Drilling
Products, based in Houston. She
is responsible for managing the
company’s drilling connections
and developing new-product
offerings. Prior to her current
assignment, she held sustaining positions and
served as product development manager for
Vallourec and other companies based in Spain
and France. Ms. Lafuente has authored several
SPE papers and technical publications related to
oilfield tubulars. She holds a Master’s degree in
Industrial Engineering from the University of
Barcelona and is currently pursuing an MBA at
the University of Houston.
ROMAIN BRANLY is a R&D engineer for
Vallourec Oil and Gas based in France. He has
10 years experience with company developing
drill-pipe connections and providing
technical support. He has participated in the
development and/or improvement of multiple
VAM casing-tubing connectors and drilling
sub products. Mr. Branly holds an MS degree
in mechanical/industrial engineering from
ENSIAME engineering school, Valenciennes
University, France.
Printed in U.S.A.
62 JANUARY 2016 / WorldOil.com
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