Crude production from Statfjord, a Statoil-operated North Sea field, is in decline. Well over 60% of the Stock Tank Oil Originally In Place (STOOIP) is already recovered, and this recovery factor is expected to reach 68% over the next few years.
The Statfjord late life project is intended to improve recovery from the field and keep it on stream until 2018–20. This will be achieved with an extensive well programme as well as modifications to the platforms. The associated Tampen Link pipeline is also being laid to export increased gas output.
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 was 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 change of strategy will increase the recovery factor for natural gas from 54% of recoverable reserves to almost 75%.
CHANGE OF STRATEGY
Statfjord is currently an oil field with associated gas, but the late life project will convert it to a gas field with associated oil. Statfjord late life is a commercially marginal project which calls for substantial reorganisation and efficiency improvements. Executing it will be a big challenge.
Statfjord B and C need substantial upgrading to produce gas. The A installation is already equipped for low-pressure output, and its adaptations and well programme will both be limited.
Modifications will be carried out while all three platforms are in full operation and without disrupting production to any extent. At the same time, safety levels must be maintained.
The limited amount of planned prefabrication means that most of the work will be done offshore, amounting to about three million hours over at least four years. In addition, there will be about three million engineering hours on land as well as some prefabrication.
Covering more than 70 of the 124 existing wells on the field, the well programme includes drilling sidetracks and recompleting for installing gas lift and sand control equipment. Processing facilities will be de-bottlenecked and modified to accept gas at lower pressure, and have their health, safety and environmental standard and technical condition enhanced.
Modifications are being pursued in two phases, with the first of these running from the autumn of 2005 to the second half of 2007. This will embrace installation of gas lift and sand control in a number of wells as well as upgrading of topside HSE standards and technical condition, including in the drilling facilities.
Due to extend from the autumn of 2007 to the end of 2009, phase 2 involves conversion of production equipment to receive and treat oil and gas under lower pressure. The drilling programme will also continue.
Estimates indicate that recovery will increase by about 32 billion cubic metres of gas, 25 million barrels of oil and eight million tonnes of Natural Gas Liquids (NGL) compared with continuing the present production strategy.
The late life project calls for the construction of a new gas export facility to the UK. The 23.1km Tampen Link pipeline will be laid from Statfjord B to the Flags transport system, which runs from the UK’s Brent field near Statfjord to St Fergus in Scotland.
Gas from the UK share of Statfjord is already piped to land
through Flags via the Northern Leg Gas Pipeline (NLGP).
Late life modification work will also tie the new pipeline into existing pipelines on Statfjord, such as those from Gullfaks and the Gassled transport systems. This will increase export capacity for Statoil gas from other fields on the Norwegian continental shelf.
The pipeline is due to be laid in 2006, and to be ready for gas export on 1 October 2007.
The Statfjord late-phase development is costed at NOK14.5bn in current money, while the Tampen Link – including pipeline-related modifications on Statfjord B – will cost NOK1.5bn. About 60% of the investment relates to modification of the installations, 30% to the drilling and well programme and 10% 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. The modified operating solution for Statfjord will reduce annual emissions of carbon dioxide and nitrogen oxides by 38% and 28%, respectively in 2007.
Produced water volumes will remain unchanged from today’s levels. 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.