Statoil looking to light intervention to lift productivity from subsea wells
Developing the capability to intervene in subsea wells registers highly in Statoil’s plans for improved oil recovery. The company is particularly active in the area of light well intervention (LWI), with one program due to kick off in mid year, another due for award by this fall, and an ongoing technology development about to move into a new phase.
Statoil has interests in nearly 300 subsea wells, and this number is set to increase further. The wells are both in the Tampen area of the North Sea, on fields such as Statfjord, Gullfaks, Vigdis, and Tordis, and the Halten/Nordland regions in the Norwegian Sea, where the currently producing Åsgard, Heidrun, and Norne fields will be joined later this year by Kristin.
More than half the company’s production comes from subsea wells, which explains why improving their recovery factor is such a priority. Subsea wells are in general less productive than platform wells, largely due to the fact that platform wells are easier to access for maintenance purposes. The key to improving subsea productivity lies in developing cost-effective intervention methods.
The company decided at an early stage that the best solution in this regard for LWI work would be lighter vessels with dedicated equipment, rather than relying on mobile drilling units, which tend to be over-dimensioned for such work. With drilling rig dayrates soaring, and availability limited, that decision looks far-sighted. But it also carries challenges, such as the development of suitable intervention equipment and systems.
This is essentially a new market, which lacks a regular flow of work from other operators in either the Norwegian or UK shelves. So despite the large numbers of subsea wells in both sectors, Statoil has also had to find ways of supporting contractors willing to assume the risk of investing in this type of work.
In 2003, the company carried out its first LWI program on new generation 7-in. monobore subsea trees, using equipment and services from FMC Kongsberg Subsea on Prosafe’s semisub construction vesselRegalia. Downhole work on three wells was completed successfully, according to Øyvin Jensen, Statoil’s operations manager for Tampen drilling and subsea operations.
This year, CalDive’s monohull intervention vesselSeawellmanaged another campaign. In this case, Statoil and CalDive jointly developed new equipment that included a lubricator for use with horizontal subsea trees as well as vertical trees. Interventions were undertaken in wells down to 300 m water depth, although the equipment could be used down to 600 m. Included in the program were a couple of high-pressure gas injectors on Åsgard. Special equipment developed for this task included a subsea grease pump.
CalDive performed interventions on five wells in this campaign, including four on Åsgard and one on Statfjord. Due to delays, the program had to be mounted out during the winter months (October 2004 to February 2005). Weather conditions happened to be worse than normal, leading to long periods of downtime. However, the downhole operations went to plan.
Statoil subsequently decided to exercise one of its options on the CalDive contract, and in mid year,Seawell was about to start a 160-day campaign. Statoil has 15 wells it would like to work on, but it remains to be seen how many can be done in the period, Jensen says. The planned program includes production logging, reperforation, and water shut-off.
The company has set stiff cost targets for LWI work - NKr1 million for a day’s work, and no more than NKr5 million for an intervention operation. A clear trend to more efficient operations can be seen since the first interventions in 2003, but there is still some way to go before these targets will be met, according to Jensen.
But operationally, the results have been encouraging. Production from wells on which intervention has been carried out has improved, and valuable data has been collected for reservoir management and validation of reservoir models, he says.
Statoil is gaining valuable experience as more operations are carried out. Taking this on board, last year it drew up specifications and tender requirements for a long-term contract for wireline operations. Bids were submitted earlier this year and evaluation was in the final stages around mid year. An attractive prize awaits the winning contractor, with a requirement for around six months’ work annually over a period of several years.
At present, the company’s needs are confined largely to wireline work. But in the longer term, it also needs a coiled tubing availability to undertake tasks such as pumping, wash-out, clean-out, and scale cleaning in long horizontal wells sections.
Statoil is engaged currently in a joint industry project with Subsea 7 to develop a purpose-built deployment system for handling coiled tubing. This would be a cost-effective alternative to using a standard riser system. In mid year the project members were looking to arrange fresh funding to move ahead to a new phase.
In parallel with the technology development, Statoil also has to win the backing of the relevant licensees for intervention operations. For the long-term contract, which will involve work on most of its fields, eight to 10 license partners have signaled their commitment.•