The main challenge for subsea technology on the shelf is increased recovery from subsea wells, Director General Gunnar Berge said at the opening of a large international conference concerning subsea technology in Bergen. Approximately 40 % of the production from the shelf derives from completed subsea wells. This percentage is increasing. In a few years more than half of the production on the shelf will come from this type of well, he said.
There has been a tremendous increase in the use of subsea completed wells since the first were put on production in the early 80s, Berge said. Approximately 380 subsea wells are in operation and more are underway. Both Snøhvit and Kristin will be developed using subsea wells. The development plan for the Ormen Lange field is also based on subsea well completions.
The latest estimates from the NPD show that the total resources on the Norwegian continental shelf are 12.9 bcm oil equivalents.
• 29% has been produced
• 32% remains in fields as reserves
• 10% is considered as contingent resources in both fields and discoveries
• 3% is related to possible future measures for increased recovery
• 26% is in undiscovered resources.
A large portion of the remaining, undeveloped discoveries lie close to existing infrastructure. Several of these will be developed as subsea satellites. Actual distance and water depth make for the use of known technology. The challenge ahead consists of making this technology more cost-efficient, Berge said.
Approximately 65% of the undiscovered resources are thought to lie in prospects that have not yet been drilled. A prospect is a mapped structure that has the potential to contain oil and gas. The remaining 35% are in plays or delimited areas where a specific set of geological factors exist and where one assumes there are prospects. The potential prospects in a play are not mature enough to be a goal for exploratory drilling.
A study of the 1,000 prospects that are registered in the NPD prospect database shows that 65% of these lie in less than 400 m of water and are less than 50 km from existing infrastructure or land. This implies that the possibility of tying back possible discoveries to existing infrastructure is high, because the technology exists. The challenge consists of developing the technology to be more cost-efficient. Subsea development of the remaining prospects relies on development of multiphase flow and subsea separation technology, he said.
Many of the discoveries and prospects that can be developed with subsea solutions lie in the mature areas of the continental shelf, where sufficient infrastructure exists and the geological aspects are well known. The potential of making more finds is large, Berge said, but exploration has to be increased.
The recovery factor represents a challenge for completed subsea wells. A study performed by Statoil, Hydro, and the NPD shows that the recovery factor from subsea wells is 15-20% lower than from wells with direct platform access. There are several reasons for this. The accessibility to completed subsea wells is more difficult and represents a larger cost than wells drilled from a fixed installation. Even for minor jobs, a boat or mobile rig has to be used. The number of mobile units available for this work in the North Sea is limited. This can lead to lack of well maintenance, thus reducing the recovery from the well. A huge effort has been made in the last years to have mobile units available. In cases where the subsea wells are far from the processing unit, keeping necessary pressure high enough over time to maintain tail production can be difficult. It is also important to collect data from these wells to optimize reservoir management. This implies a technical challenge, but also a potential gain, Berge said. The NPD is glad to see Statoil's goal of achieving an oil recovery factor of 55% from subsea-completed wells within 2008.
It is the NPD's opinion that the technology to build light intervention vessels or rigs is available and under constant development. But up to now the development risk has been carried mainly by the suppliers. To succeed in building these mobile units, the operating companies must take further responsibility and work hand-in-hand with the industry.
03/17/04
