Successful Grane pre-drilling
Pre-drilling on the Hydro operated North Sea field Grane, 185 kilometres west of Stavanger, has been a success. The programme was completed within budget two months ahead of schedule, and included the drilling of two more wells than originally planned.
Pre-drilling, which commenced 1 September 2001 and was completed on 7 January this year, included nine production and three injection wells.
Given the nine pre-drilled production wells, Grane will produce 70 percent of plateau production before drilling of the remaining production wells commences on the platform.
Two of the injection wells now drilled will be used to inject gas for pressure support in the reservoir, while the third will inject cuttings and produced water.
A total of 35 wells are to be drilled on the field, of which 27 will be production wells. The remaining wells will be drilled from the Grane platform, where Odfjell Drilling will be responsible for drilling operations.
" The crew of the Saipem-owned drill rig Scarabeo 6 have done a great job, working well together with the Grane field's Bergen based rig team," says offshore installation manager Svein Hatlem, who doubles as Hydro Oil and Energy's representative for the development.
One of the reasons for the success of the drilling programme was the thorough planning. As the Scarabeo 6 rig has limited storage space, Hydro's rig team has stressed that there is only room for absolutely essential drilling equipment.
"Grane's land-based rig team and drill rig crew were able to predict which equipment would be needed. Had this not been as accurate as it was, we would have had a lot more downtime when weather conditions prevented us from transporting new supplies," says Hatlem.
New drilling technology
The application of new drilling technology has played a vital role during the pre-drilling programme. In conjunction with Schlumberger Oilfield Services, Hydro has developed and started to use the new "Ultra Deep Resistivity Tool".
" This technology has provided us with the opportunity of placing the well-paths in a better position with a view to maximum production and recovery," says Hatlem.
In many of the production wells the path enters the reservoir horizontally, at a distance of between nine and 16 metres to the oil-water contact point. However, in wells where there is no water at the bottom of the reservoir, the wells penetrate as deeply as possible.
" The new technology gives us the opportunity to "see" the bottom of the reservoir around the drill bit, allowing us to manoeuvre accordingly," adds Hatlem.
The Grane drill team has also tested the use of seismic investigations during drilling. It has been documented that this technology enables one to "see" 300 to 400 metres ahead of the drill bit when drilling.
Ninety percent of the Grane development has now been completed and work is on schedule for production start-up in October. The development has also been kept within the total budgetary cost limit of NOK 15.5 billion, one billion less than indicated in the Plan for Development and Operation (PDO).
Furthermore, by 15 December all platform modules were completed and are currently being tested at AkerKværner's yards at Stord, Egersund, Stavanger and Verdal.
In the spring the modules will be transported to the Grane field, where they are scheduled to be installed between April and June.
Grane licence holders
Norsk Hydro (operator)