January 2016
Oilfield Technology |
53
that is a hybridised version of a double shoulder
connection and the gas tight connection from a
drill-pipe-riser. Qualification of the new product
was performed on the most critical sizes and
involved industry standard physical testing
including make-and-break, overtorque, combined
loading and fatigue testing. This connection
is qualified to 30 000 psi internal pressure and
25 000 psi external pressure.
Comparison with common connections
The primary criteria for developing a gas tight
connection for deepwater operations included safety,
ease of use, and robustness.
In today’s market, available connections – such as
standard API, premium double shoulder connections,
drillpipe risers and OCTG based connections – only
fulfil some of the above criteria.
Based on these three criteria, below is a
brief comparison and summary of the existing
connections:
API drill pipe connections
API connections do not offer gas tight capability
and thus can potentially create health, safety and
environment (HSE) hazards, especially for demanding
applications such as deepwater stimulation
operations. API connectors have been designed to
be extremely robust and the threads and sealing
faces have low sensitivity to galling to resist harsh
drilling practices. With robustness comes fatigue
resistance. Although this type of connection is the
right fit for a lot of drilling operations, it can be risky
for completions and other technically challenging
applications.
Premium drill pipe connections
For more demanding applications, double shoulder
connections are designed to provide improved performance
while drilling, compared to API connections, primary
improvements are based on mechanical performances. They
are easy to use and as robust as API drilling connections.
Though this type of connection has been used for drilling
operations and some completions applications, gas tight
performance would still be inadequate for the more
challenging offshore hydraulic fracturing operations.
Riser connections (drillpipe based)
These products are specifically designed to be used in
work over/intervention/completions operations, hence
these products have been designed with excellent fatigue
resistance characteristics and can have gas tight ratings up
to 10 000 psi. The primary restriction of these products is
that they provide limited flexibility since they are designed
for completions operations.
OCTG connections
These connections are very application specific, and can be
more sensitive to galling on the thread and seal areas, which
mandates cautious handling techniques. These connectors
can be used for deepwater applications and criteria for
selection really depend on the preferred completion design.
Design criteria
Primary objectives for the development team when working
on this connection was to design and qualify a connector
with a minimum gas tight rating of 20 000 psi, offers the
ability to be handled like a drilling product and is robust by
design.
The already-existing double shoulder drilling connection
provided the foundation for such development and this
Figure 1.
Seal engagement andmake-upprocess.
Figure 2.
Longmake-up curve (FEA).
