Drilling Laggan-Tormore

The offshore drilling of Laggan and Tormore requires two separate campaigns, the first of which is scheduled to commence once both subsea templates are successfully installed in summer 2012.

Phase One consists of seven individual wells: four on Laggan and three on Tormore. A second campaign will see a further well drilled on each, after 12 months of production to evaluate the dynamic response of the fields.

Vertical exploration wells have already been drilled on both fields, as part of TOTAL E&P UK’s initial exploration in the area, and one existing exploration well on Tormore will be re-entered and completed during the Phase One drilling campaign.

Technically challenging

The TOTAL Group has extensive experience of deep water drilling from its global operations – knowledge that continues to inform and guide the planning and eventual execution of the drilling campaigns for Laggan and Tormore.

However, drilling in the West of Shetland region, on the edge of the UK Continental Shelf, still represents a significant challenge for TOTAL’s E&P UK’s drilling teams.

In water depths exceeding 600m, drilling rigs – traditionally the work-horses of the North Sea oil and gas industry – struggle to provide the required stability during heavy sea swell conditions.
Located 140km north-west of the Shetland Islands, winter sea states can be severe, creating difficulties to conduct operations and logistical problems when re-supplying the rig. “Despite the rig selected is suitable for all year operation in West of Shetland, anticipation and flexibility will be required to cope with the often severe weather conditions,” explains Robert Baiget, Drilling and Completion Team Leader.

“Respect of the environment is critical and all the cuttings produced with oil based mud will also be offloaded for onshore treatment and proper disposal,” adds Robert.

The West Phoenix, a recent semi-submersible rig operated by Seadrill , has been contracted to complete the drilling campaign. The rig is scheduled to remain on station throughout winter 2012 and 2013.

The drilling string

Stability and station keeping are vital factors when drilling at these water depths. This is especially true when drilling in ‘open water’ before the installation of risers to help support the drilling string.
Once riser has been installed, drilling is protected to a degree but sub-surface currents throughout the water column will also create important efforts to the drilling riser and induce high fatigue levels at the wellhead, which have to be taken into account at the design stage. 

“With a destination depth to the reservoir of approximately 3,000m vertical below the seabed, in terms of reservoir depth and horizontal offsets, drilling Laggan and Tormore is very much within normal operational parameters,” says Robert. “The pressures and temperatures within both reservoirs are not very high. However, we’ve never attempted directional horizontal drilling in the West of Shetland region before, so our initial experiences will inform how we approach the later wells.”