"Upgrading the drilling equipment is essential if we are to implement the comprehensive drilling programme for the Statfjord B platform. The new drilling equipment will also realise major benefits with respect to health, safety and the environment," says Colin Briggs, project manager for the drilling equipment upgrades.

Primarily, the upgrade involves replacement of the electrical system, and installation of a new lift device and new drilling machine that will ensure that the drilling equipment is more robust and reliable (Fig.1).

The drilling equipment on the platform has been shutdown while work is in progress. When the equipment is ready to use again in March next year, it will be possible to drill with increased regularity.

As many as 80 people will be working on modifications while the platform is fully operational. Plans for the first 80000 hours of work have been finalised, with the first major challenge the need to lift aboard a new electrical module.

Upgrading drilling equipment on the Statfjord platforms will continue until 2010. After modernisation, the drilling equipment on the three Statfjord platforms will have the same functionality and equipment.

"The next stage of the upgrade covers new equipment for handling drill pipes, and upgrade of the modules for drill mud. This will further improve the robustness of the drilling equipment, and significantly improve the working environment," explained Petter Kostøl, head of drilling and wells Stavanger.

StatoilHydro is investing NOK2.3billion (US$450m) in the Late Life project in 2008 (see below), and will use an additional NOK2billion (US$390m) on operation, maintenance and modification of the field this year.

"We are investing heavily in maintenance and upgrades as part of our preparations for long-term operation of this important section of StatoilHydro operations on the Norwegian continental shelf. This is just one of many projects which will contribute to efficient operation on the Statfjord B platform in the future," added Lars Petter Lundahl, head of Statfjord production.

The drilling upgrade of this platform will require 175 000 work hours between 1st June 2008 and March 2009. Up to 80 people will be working on the upgrade at any time. All electrical systems for the drilling equipment will be replaced, while the cables will be re-used wherever possible. Seawell Norge is the main contractor, and is supported by the Grenland Group and Profitek. National Oilwell Varco and Wartsila Norway are the main suppliers of the equipment used in the upgrade

The Late Life project

The Statfjord Late Life project is intended to improve recovery from this StatoilHydro-operated North Sea field and keep it on stream until 2019.

This will be achieved with a very extensive well programme as well as modifications to the platforms. The associated Tampen Link pipeline is also being laid to export increased gas output.

Crude production from Statfjord is in decline, with well over 60percent of the stock tank oil originally in place already recovered. This recovery factor is expected to reach 68percent over the next few years.

Injecting gas and water to maintain reservoir pressure has been an important element in the present production strategy for the field. Combined with an extensive programme of drilling wells to tap remaining oil pockets, injection has helped to push the recovery factor much higher than expected when development began.

By reducing pressure in the reservoirs and on the platforms, large volumes of previously-injected gas can be recovered. Gas will also be released from the remaining non-recoverable oil. This will increase the recovery factor for natural gas from 54percent of recoverable reserves to almost 75percent.

Statfjord is currently an oil field with associated gas, but the late life project will convert it to a gas field with associated oil.

About 60percent of the investment relates to modification of the installations, 30percent to the drilling and well programme and 10percent to the pipeline.

Improving recovery from Statfjord will enhance revenues. The project will also boost activity and create opportunities for further business development. Converting existing platforms will be significantly cheaper than building new installations. Modifying them during production avoids loss of revenue from long shutdowns, says the company.

The modified operating solution for Statfjord has already reduced annual emissions of carbon dioxide and nitrogen oxides by 38 and 28percent respectively. While produced water volumes will remain unchanged, technology for water treatment has been installed to meet the official requirement for zero harmful discharges to the sea. Oil-based drilling mud and drill cuttings will be injected below ground.

Covering more than 70 of the 124 existing wells on the field, the well programme includes drilling sidetracks and re-completing for installing gas lift and sand control equipment. Processing facilities will be modified to accept gas at lower pressure and debottlenecked, and have their health, safety and environmental standard and technical condition enhanced. o