Wellslot creation helps evolving Hewett
  from: Offshore Engineer
  by: David Rowson
  Thursday, October 02, 2008

Engineering and business ingenuity are key to maximising hydrocarbon recovery from mature North Sea fields and ensuring the more long-in-the-tooth structures remain fit for purpose. Aquaterra Energy recently completed a $2 million structural project to install an additional wellslot on a 40-year old gas platform. Project manager David Rowson reports.

Operator Tullow Oil asked Aquaterra Energy to review the feasibility of installing an additional well on the Hewett field 48/29A platform, located 28km north-east of the Bacton terminal in the southern UK North Sea. Several options were identified, including a number of potential wellslot locations, a slot recovery option and a bridge-linked wellhead platform option, based on its Sea Swift platform technology.

After careful deliberation with Tullow Oil, a new wellslot location, adjacent to the existing wellbay area, was selected as the preferred option. Aquaterra Energy was awarded the contract to project manage the structural element of the work.

The company’s scope of work comprised project management from design and onshore fabrication through to offshore installation. Great Yarmouth based KSD Fabrication was selected as the fabrication and installation contractor.

Aquaterra Energy plan to create a new wellslot through the platform involved significant structural modifications to the topsides and the addition of conductor guides within both the topsides and the jacket structures – above water level.

At main deck level one of the existing primary beams had to be ‘by-passed’ with reinforcing beams before removing the beam to create the opening for the new well. New conductor guides were provided at both cellar deck and spider deck levels.

Because of the relatively shallow water at this location – around 23m (75ft) – a riser analysis to design an optimal conductor riser was undertaken in-house.

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 activities.

The 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 that it fitted ‘first time’.

In addition, a complex subsea camera survey operation was also undertaken to ensure a clear conductor path through the jacket structure. 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. Drilling of the well began in August.

The project was seen as a great success by Tullow Oil; and was one undertaken on schedule, within budget, and, most importantly, safely.

Aquaterra Energy believes that the venture will open up further opportunities for similar business, particularly in mature fields, using the company’s multidisciplinary expertise in both platform engineering and drilling engineering. Many of these older structures are heavily used with little space for expansion. But the innovative creation of a new wellslot can result in significant cost savings when compared to a subsea development or a new satellite platform.OE

About the author

David Rowson is a project manager with Aquaterra Energy with more than 20 years engineering and project management experience in the oil and gas industry. Rowson is a chartered civil engineer with a BEng (Hons) in civil and structural engineering from the University of Sheffield.

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