When Ekofisk was first developed in the 1970s, it was thought that only 17% of reserves could be recovered. Based on original plans, the field would have finished producing already. Thanks to efficient operations and improved oil recovery, Norway’s very first oil field development is expected to keep pumping until 2050, according to the Norwegian Petroleum Directorate.
New technology has played a very important role in increasing recovery. It makes it possible to drill wells and develop fields in ways not technically feasible before.
Ekofisk is just one of many example of how the industry has been able to recover twice as much oil on the Norwegian shelf as the global average. Worldwide the expected oil recovery factor is less than 25%, according to INTSOK, the government supported initiative to help the Norwegian oil industry expand abroad. The rate on the Norwegian shelf is currently close to 50%.
Statoil, the largest operator on the Norwegian Continental Shelf, has set even more ambitious targets. The Norwegian oil company has ambitions to achieve an average 65% recovery rate on its platform operated fields and 55% from subsea fields. It will do so by intensifying research and development in areas and quickly adapt and apply the R&D results to its fields.
Framo, for example, was recently given a contract to develop a solution for subsea wet gas compression that could extend the life of the Gullfaks South field. The technology lets Statoil compress gas closer to the reservoir rather than on the platform. The goal is to boost recoverable gas reserves by 6% from the current estimate, representing 3 billion standard cubic metres of gas.
|Statoil and FMC Technologies have developed new well and sidetrack technology, Through Tubing Rotary Drilling (TTRD), to improve oil recovery from subsea fields.
Statfjord Late Life
Statoil has made great progress in various oil recovery methods, ranging from water injection for pressure support to various advanced procedures for improving oil recovery, such as water-alternating-gas, also known as WAG, injection.
In some of the larger fields, such as Gullfaks and Statfjord, the company has been able to nearly double the ultimate expected recovery factor from 40% to 70%. The most important IOR measures for these two fields were advanced wells, well intervention, 4D seismic, produced water management, and topside modifications, according to INTSOK.
Statoil expects to prolong the life of the Statfjord field by 12 years, extending its lifetime by two more years than expected when the plan for Statfjord Late Life programme was originally submitted. The overall value creation from these additional reserves is worth NOK 60 billion, a six-foldincrease since the Statfjord Late Life plan was submitted in 2004.
“We are highly satisfied with every single year we can add to the Statfjord field’s productive life,” said Ståle Tungesvik, Statoil Senior Vice President for the operations west cluster in the Exploration and Production Norway business area.
Statoil and its license partners will invest in eight new electrical semisubmersible pumps on the Statfjord C platform, and possibly another four for Statfjord B, to pump out the water out of the reservoir. This will lower the reservoir pressure and release more gas for production.
There are several INTSOK partners that provide pumping and compression solutions. Aker Solutions and FMC Technologies offer multiphase pumping and compression solutions. Framo Engineering delivers water injection pumps, multiphase pumps and wet gas compressor. PG Pump Solutions has multiphase pumps, while Siemens Oil and Gas Offshore offers wet gas compressors.
But the single best way to improve oil recovery is better drilling methods, according to Statoil. That is because a growing number of discoveries are developed as subsea installations, while productivity is declining at mature fields. Wells need workovers to remove deposits and halt water intrusion in order to maintain output. But this is more expensive on subsea developments.
“Downhole intervention and sidetracks from existing wells are the most effective ways of recovering more oil and gas from subsea fields,” said Øystein A. Håland, Statoil head of subsea technology. “Adopting new solutions in these areas also yields substantial reductions in operating costs.”
Statoil has adopted light well intervention (LWI) vessels on a large scale to cut thecost of well intervention work. It has two ships from Ulsteinvik-based Island Offshore, Island Wellserver and Island Frontier, in operation all year round on the Norwegian shelf.
A LWI vessel costs less to hire than a conventional rig. During LWI, downhole equipment is remotely operated via a wireline from the surface and – unlike rigs – without a riser. A LWI vessel is also easier to move around than a moored semi-submersible rig.
“We expect LWI to earn about NOK 15 billion in 2009,” said Øyvin Jensen, Statoil head of LWI operations. “
Statoil has also developed new well and sidetrack technology, together with FMC Technologies, to improve oil recovery from subsea fields. The new technology, Through Tubing Rotary Drilling (TTRD) lets it drill new sidetracks through existing tubing on subsea fields, rather than drill expensive new subsea wells. TTRD was successfully tested on the Norwegian field Åsgard this summer. Statoil expects the drilling operation to produce NOK 1.4 billion worth of extra oil from the Åsgard field.
There are various INTSOK partners that help with drilling relation solutions for improved oil recovery. Within well design and planning, there is AGR, IRIS, and SINTEF Petroleum Research. AGR, Geomec Engineering, IRIS, PTC and Reelwell have drilling technology and equipment. Aker Solutions, FMC Technologies, Odfjell Drilling, and TTS-Sense provide other drilling and well intervention methods. In addition, Odfjell Drilling and SeaDrill have rigs and drilling services.
|Statoil has adopted light well intervention (LWI) vessels on a large scale to cut the cost of well intervention work. Pictured here is Island Offshore vessel Island Wellserver.