“If I tell people that it would be fantastic to increase the recovery factor of Draugen from 67% to 70%, most people do not really see why that should be so exciting,” says Andrew McCann, Senior Vice President Subsurface from OKEA. “It just seems a small increment to most people,” he adds.
However, when he subsequently explains that it entails a doubling of the reserves left in the field, people get what his enthusiasm is about. It may equate to a greater volume than the average NCS present-day discovery of around 30 MMboe.
How easy is it to double the reserves of a mature asset?
In 2019, one year after the acquisition of Draugen from Shell, OKEA immediately drilled two wells in order to prove up further potential. One exploration well was drilled east of the field. Unfortunately, well 6407/9-12 targeting the Skumnisse prospect came in dry. In addition, an observation well was drilled into the attic of the field to find out if there was any significant oil left to be produced. Even though oil was found, the thickness of the leg did not justify further development.
This subsequently prompted the team to look at infill opportunities within the producing zones. “First of all, you have to understand the nature of the reservoir,” McCann says. ‘’In a way, the ‘problem’ with Draugen is that the reservoir is so good. Because of that, the entire field has been swept very efficiently. Oil remains, as it always does, but it is not necessarily sitting in undrained pockets. Instead, it is spread out all over the reservoir.
“Even though we have identified potential infill opportunities,” McCann explains, “these are just not making economic sense because the potential volume to be produced through these infill wells is too low.” So, with infill opportunities being difficult to justify and two wells drilled that did not result in tangible opportunities, OKEA had to look at other ways to up the recovery factor.
Draugen is an undead creature from Norse mythology. The Old Norse meanings of the word are revenant, undead man and ghost. Draugen live in their graves, often guarding treasure buried with them in their burial mound.
Reducing wellhead pressure
“It can sound very boring,” admits the geologist, “but we have found another solution to increase the recovery factor.” McCann alludes to the upgrade of subsea booster stations, which means that the pressure at the wellhead can be reduced by 4 to 6 bar. ‘’As a consequence of this measure, we can accelerate production and continue producing wells for a longer period and therefore get more oil out of the reservoir.’’ Even though the ultimate recovery factor of Draugen may not end up as high as the desired 70%, the above illustrates that small changes can result in significant additional value creation.
Draugen at a glance
Draugen was discovered by Shell in 1984, PDO was approved in 1988 and production started in 1993. Original reserves were estimated at 955 MMb of oil and 53 Bcm of gas and condensate. Remaining reserves are estimated to 60 MMboe by norskpetroleum.no.
The Draugen field produces oil from two formations. The main reservoir is in Upper Jurassic sandstones (Rogn Formation) while the western part of the field also produces from Middle Jurassic sandstones (the Garn Formation). The reservoirs lie at a depth of 1,600 metres, are of good quality and relatively homogeneous across the field. Hydrocarbons are produced by pressure maintenance from water injection and by aquifer support.
The iconic Draugen platform was developed using a fixed concrete facility with an integrated topside. Production is from both platform and subsea wells. Stabilised oil is stored in tanks at the base of the facility. Two pipelines connect the facility to a floating loading-buoy. At the moment, the production licence for Draugen runs until 2024, but OKEA has filed an application for it to be extended for sixteen more years, bringing it to 2040.
OKEA’s strategy
OKEA was founded in 2015 to work up stranded discoveries and marginal fields, of which the Yme redevelopment, operated by Repsol, is a prime example. With the arrival of Svein J. Liknes as new company CEO last year, the strategy was revised to be more in line with what the Draugen acquisition in 2018 already embodied – to successfully take over and manage mid- to late-life assets.
“We believe that prices will remain buoyant for some years to come,” the McCann says, “and the Norwegian continental shelf presents good opportunities to capitalise on our strategy.” With the acquisition of the Brage field from Wintershall Dea – which is subject to the customary authorities’ approval – OKEA will be able to apply lessons learned from operating Draugen to another late-life asset.
Accessing gas through Hasselmus
The Hasselmus gas discovery is a good example of how OKEA’s strategy differs from Shell’s, the previous operator of Draugen. Even though the field was discovered already in 1999, it was never developed by Shell. Now, it presents a tangible opportunity for OKEA to get access to fuel gas to run the platform which will reduce cost and in addition earn revenues from gas and condensate export. At the moment, condensate produced from Draugen itself is being reinjected. A development well will be drilled this year, with first gas expected in late 2023.
Power from shore
In addition to Hasselmus coming onstream, OKEA is also expecting to sanction a project to electrify offshore operations through power from shore. This will be done in conjunction with the electrification of the Njord platform operated by Equinor a little further to the West.
“The electrification project is also a way to extend Draugen’s field life,” McCann says: “It not only cuts the amount of gas required for the platform’s energy supply and thereby the related CO2 emissions, it lowers the operating costs due to the reduction in CO2 taxes”.
Further Exploration opportunities
“We are very aware that a proactive attitude is required towards operating late-life assets,” says Andrew McCann. That is why OKEA applied for and was awarded new licences around Draugen and that’s why we are planning to drill further near-field exploration wells. “We prefer to see the glass as half full rather than half empty.”
HENK KOMBRINK
