The PESGB thank Maersk Oil for sponsoring this Aberdeen Evening Lecture

Oil and Gas Exploration in the Danish Sector

Nils L. Jacobsen, Troels Albrechtsen and Michael Winfield, Maersk Oil

Tuesday 16 February 2010, 6pm for 6.30pm presentation
Copthorne Hotel, 122 Huntly Street, Aberdeen AB10 1SU

The first Danish exploration licence was granted in 1935 and since then there has been oil and gas exploration activities in Denmark. However, it took more than 30 years before any real success could be reported. In 1966 A.P. Møller drilled the first Danish off-shore well discovering oil in chalk of what was later to be known as the Kraka field. This discovery marks the first find in the whole of the North Sea. The subsequent discovery in 1971 of the nearby but significantly larger Dan Field was put on production in 1972 marking the start of Danish Offshore oil and gas production. 

Production of oil and gas have played an important role for the Danish economy with the production peaking in 2004 at the level of some 500 k boe/d or corresponding to about 200% of the national consumption, and making Denmark the third largest North Sea oil producer after Norway and the UK.

The current production is from 19 offshore fields all located in the Danish Central Graben. The prediction is that Denmark will remain self sufficient in oil and gas to 2020.

The majority of the production (more than 90%) is from Ekofisk and Tor Formation Chalk characterised by relatively high porosity but low permeability matrix conditions. By 2008, an average recovery of about 20% of the known resources has been achieved leaving a major challenge in trying to increase the recovery efficiency.  

More than 250 exploration/appraisal wells have been drilled many targeting the traditional chalk structures. In 1998 the discovery of the Halfdan field sparked further interest in the chalk play and added to the understanding of the more sophisticated trapping potential of the chalk in a non-structural setting. The Halfdan discovery had a significant importance for the exploration interest in the late nineties and has been responsible for increasing the potential of the chalk, particular within the flank areas of the existing fields.  

Historically a number of smaller discoveries has been made in, for North Sea conditions, more traditional sand stone reservoirs of Upper and Middle Jurassic age as represented by the Harald/Lulita and Amalie discoveries or the Palaeocene sand fairway systems at the at the Siri, Cecillie and Nini fields. A number of wells were drilled in the Danish sector during the period from 1980 to1995 for this type of reservoirs, however without major success. The lack of exploration success was mainly explained as a combination of lack of charge, insufficient trapping or in particular at greater depth; poor reservoir properties.  

The discovery of reservoir quality sands of Late Jurassic age in 2002 by the Svane-1A well at a depth of nearly six kilometres marked a renewed interest in exploring for such hydrocarbon traps in the deeper parts of the Danish sector. Seven wells were spudded in 2008, two of which were wildcat dry holes. Five were appraisal wells; two proved oil, one had shows and two are tight hole.

One exploration well was drilled (and sidetracked) in 2009, and found hydrocarbons in the Middle Jurassic, with the sole appraisal well on Ravn near the Elly discovery proving oil in the Upper Jurassic.

The Palaeozoic has been explored by a few wells targeting reservoirs within the Carboniferous and Rotliegendes, but without success, the main reason being mainly lack of effective source.  

The challenge for the continued Danish North Sea exploration success is to push the limits of high quality 3D seismic data capable of improving the imaging of the deeper structures and providing higher stratigraphic resolution so important for successful prospect evaluation and well placement.  High quality seismic and in particularly availability of 4D data has in addition allowed drilling of smaller chalk targets. Basin modelling studies have given increased insight helping to de-risk charge and reservoir effectiveness allowing exploring for even smaller and more complex prospects in a mature province where most of the obvious structural targets have now been drilled. 

With respect of the Danish on-shore and in-land waters the initial thirty years of exploration activities from 1935 to 1965 focused there inspired by some success in Northern Germany. Most of the obvious salt structures were drilled during this period along with prospects defined along the rim area of the Zechstein basin in southern Jutland and across the islands within the inland waters towards the east. This activity ceased in the early eighties without demonstrating commercial success. Today, however, it seems like interest is re-emerging with a couple of operators in the process of maturing wells on older prospects along this trend. Also prospects on the flank of the Ringkøbing-Fyn High seem have found renewed interest.

In the Skåne province of southern Sweden Shell spudded the first of three planned wells (c.1000 m TD) in November, 2009. The objective is the Cambrian Alum shale and the well was positioned with the aid of newly acquired 2D seismic. In the same month, Devon applied for two “Open Door” licences in Denmark, likely targeting shale gas in northeast Sealand and northern Jutland, both on trend with Shell’s Swedish concession. Several wells drilled in the areas between 1949 and 1985 failed to reach the Cambrian.    

So maybe the Danish on-shore area is due for a revival after more than 30 years of North Sea off-shore success?

References 

1) Denmark’s Oil and Gas Production 08, Danish Energy Agency, June 2009