tullow oil
slot addition
case study
THE CHALLENGE
Operator, Tullow Oil, was looking to install
capacity for an additional well slot on the Hewett
field 48/29A platform, located 28km north-east
of the Bacton terminal in the southern UK North
Sea.
THE CONTRACT
Having undertaken a feasibility review, Aquaterra Energy
highlighted several options including a number of potential
wellslot locations, a slot recovery option, and a bridgelinked wellhead platform option utilising its Sea Swift
platform technology. The company was subsequently
awarded the contract to project manage the structural
element of the work, from design and onshore fabrication
through to offshore installation.
EXECUTION
A new wellslot through the platform was created, which
involved significant structural modifications to the topsides
and the addition of conductor guides within both the
topsides and the jacket structures. At main deck level, one
of the existing primary beams had to be by-passed with
reinforcing beams, before removing the original beam to
create the opening for the new well. New conductor guides
were provided at both cellar deck and spider deck levels.
The relatively shallow water at the location – around 23m
(75ft) – highlighted that there was potential for a solution
to be developed whereby no subsea supports were needed.
This meant that as a first step a riser analysis for the design
of an optimal conductor riser was undertaken in-house to
try to meet this high value objective.
The analysis demonstrated that a conductor configuration
could be installed without the need for additional subsea
clamps. This significantly reduced the project costs by
eliminating fabrication and installation of subsea clamps,
and completely removed the need for any diving facilities.
Installation of the spider deck conductor guide and clamps
involved a complex lifting and rigging operation. Accurate
dimensional control was a key consideration with this
structural component during initial site surveys, design,
fabrication and installation, to ensure a precise fit.
In addition, a complex subsea camera survey operation
was executed to ensure a clear conductor path through the
jacket structure – this platform was around 40 years old
and obtaining accurate records on close proximity members
which could clash with the new conductor was very difficult.
This survey was on the project critical path and was a
potential ‘show stopper’.
The use of Aquaterra Energy’s low-cost and innovative
Aquascope multi-camera system, lowered through the
jacket structure, saved the client the expense of mobilising
an ROV spread, while providing superior dimensional data.
RESULTS
The project was seen as a great success by Tullow Oil - it was completed on schedule, within budget and, most
importantly, safely.
Aquaterra Energy believes that this project showcases the opportunities that can be realised, particularly in mature
fields. Many older structures are heavily used with little space for expansion, however, the innovative creation of
a new wellslot can result in significant cost savings when compared to a subsea development or a new satellite
platform.
Jim McGilvray, Project Manager for Tullow Oil said: “We have had excellent service with no surprises from Aquaterra
Energy on this project, which included the construction of a new platform conductor slot and carrying out an
associated tricky sub-sea structural survey.
“We have seen thorough, detailed engineering, delivered professionally, on time and within budget. I have
recommended Aquaterra Energy to all of my engineering colleagues within Tullow Oil and to friends in other
companies. It’s refreshing to work with such professional people.”