First Coiled Tubing Operation in Alaska Requiring 15,000-psi-Rated Well Control Equipment: A Case History
Drilling activity in remote, complex environments has increased in
Alaska as operators seek to combat falling production in existing wells and
shift to commercialization of natural gas and condensates. The completion of
these wells often requires coiled tubing (CT) intervention, whereby CT is used
for various applications, including wellbore cleanout, milling, fishing, and
acidizing operations. To complete multiple high-pressure wells in a remote
field, an operator required a CT contingency to shift formation isolation
A new collaborative approach was implemented in which the operator and
CT service provider closely worked together on the technical job design from
the onset of the project to optimize planning and execution. The planned
intervention was part of a large project in which a single company provided
most of the services. This allowed the CT service provider to work closely with
the operator and third-party providers, such as the fluid supplier and
completion equipment supplier, to complete key technical design elements,
including CT string design, fluid design, and downhole tools selection. In this
way, an integrated, fit-for-purpose solution was delivered to the operator.
Many key challenges were associated with this intervention. The biggest
challenge was the absence of previous such experience in a well in Alaska where
maximum allowable surface pressure (MASP) exceeded 8,500 psi. The intervention
would require well control equipment and other pieces of treating equipment and
downhole tools rated for 15,000 psi that were not readily available in Alaska.
In addition to the well's high MASP (8,564 psi), other key challenges included
being ready to perform a CT milling operation of a formation isolation valve in
large casing (7 5/8 in) in an environment with 30-ppm H2S and 4.55%
CO2 where ambient temperatures could drop as low as −50 degF.
A 2-in. CT string with a length of 19,000 ft was designed to provide sufficient
weight on bit and overpull to complete all required contingency CT operations.
A fluid system was designed to not only control the high pressure in the well
but also be pumped through the CT string at circulating pressures that did not
exceed the limits of the pipe. Furthermore, a test was completed prior to the
mobilization of equipment to location to determine the optimal design for
milling the formation isolation valve with CT.
This paper presents the job design and preparation processes completed
for the first planned CT intervention contingency in Alaska, in addition to
lessons learned that can be applied to future high-pressure CT operations
requiring well control equipment rated to 15,000 psi.