A total of 19 new well sections were drilled in the Danish fields in 2009: 11 production wells, including one with two well sections, five water-injection wells, one appraisal well and one exploration well. Thus, drilling activity remained at the same level as in 2008.
The above-mentioned wells and additional development activities represented total investments of DKK 7.05 billion, an increase of almost 20 per cent compared to 2008.
Appendix B contains a description of the individual fields, including development and investment activities, as well as maps showing the location of the most important wells.
Approved development plans and ongoing activity The Dagmar Field
The operator is working to reassess the field’s potential and has so far concluded that the field has residual potential which it may be possible to exploit. A final plan is anticipated during 2010. The field is therefore not facing imminent decommissioning and removal of the installations.
The Dan Field
During 2009, maintenance (see box 3.1) was carried out on five old wells. These wells have been restimulated (see box 3.2) and zones with a risk of water breakthrough have been closed.
The Gorm Field
In mid-2009, well N-40B was drilled as a redrilling of well N-40A. A collapsed section of N-40A could not be restored and the well had to be closed. As there is still the potential for producing oil at the location, the well was replaced with a redrill from the old well. The new well, N-40B, is located parallel to the original well. The redrill has shown positive production results.
The Halfdan Field
In December 2008, the operator applied for approval of a plan to further develop the northeastern part of the Halfdan Field. The plan comprises drilling and subsequent
Box 3.2
Stimulation and restimulation
A very simple description of the principle of an oil well is that a pipe connection is established from the platform to the reservoir that contains hydrocarbons. In the section of pipe that is located at the very bottom of the reservoir, a series of holes are made to allow hydrocarbons to flow into the pipe and then continue up through the pipe to the platform.
To increase production, a stimulation treatment of the well is carried out imme-diately before the well is brought on stream. Stimulation is a process where dilute hydrochloric acid is forced out through the well’s holes under high pressure. This results in some of the calcareous material in the reservoir being dissolved and increases the surface area, which improves production. When the well has been producing for a period of time, it may be necessary to repeat the stimulation pro-cess in order to re-optimize the flow conditions to the well. This repeat stimula-tion is called restimulastimula-tion.
Box 3.1
Maintenance activities on offshore structures are often called workovers (WO) or well interventions.
Workover activities can comprise restimulation (see box 3.2) or installation, replacement or repair of mechanical equipment on the platform or in the well.
Well interventions can comprise the clean-up and removal of undesirable materials such as sand or chalk that seep into the well during production, or scale that is formed when injected seawater reacts with formation water. Sand, chalk and scale can all plug the well. Well interventions can also comprise zone adaptation in the wells. Some wells are completed with separate zones in the reservoir section. These zones can be opened or closed in order to optimize the production of hydrocarbons.
Well interventions are often carried out using equipment that is secured to a wire or coil tubing and controlled from the platform or a drilling rig adjacent to the platform. Whether a drilling rig has to be used for the work will depend on the scope of the maintenance work and the design of the platform.
Several restimulation campaigns were carried out in 2009.
production from another two dual-lateral gas production wells, 1ML and HCA-9ML; see box 3.3. The wells were approved individually in January and April 2009 respectively. Total production from the two wells is estimated at 0.97 billion Nm³ of gas and 0.08 million m³ of oil.
There was considerable drilling activity in the Halfdan Field during 2009. A total of nine new wells were drilled, of which the last was completed in early 2010.
Three gas production wells were drilled using the drilling rig Ensco 71: HCA-4ML, HCA-1ML and HCA-9. All three wells were located so as to form part of the existing helical pattern extending from the HCA platform. HCA-9 was originally planned as a dual-lateral well, but was drilled with only a single well section for technical reasons.
All three wells produce from a reservoir of Danian age.
In the western part of the Halfdan Field, oil production well HDA-29 and water-injection well HDA-39 were drilled using the drilling rig Noble Byron Welliver. Both wells were drilled in a western extension of the existing, regular well pattern and are located in a reservoir of Upper Cretaceous age. In the northwestern extension of the same regular well pattern, there were originally plans for seven new wells from the HBB platform. This has been reduced to five wells, HBB-1, HBB-6, HBB-7, HBB-8 and HBB-9, which were drilled using the drilling rig Energy Endeavour in 2009. HBB-6 and HBB-8 are water injectors, and the other three wells are oil production wells. The drilling of HBB-9 was begun in 2009, but work on the well was not completed until 2010. This is because the original plan for HBB-9 was revised and the well has been extended towards the northwest to a total well length of 31,140 ft, which corre-sponds to approximately 9.5 km. The well is therefore Denmark’s longest horizontal well.
In addition to well operations, a 20” multiphase pipeline from Halfdan (HBB) to Dan F was replaced.
Box 3.3
A well with two or more well sections targeting the reservoir is called a dual-lateral or a multidual-lateral well.
A multilateral well only needs one individual wellhead on the platform. From the seabed to the top of the reservoir, the well is drilled as an ordinary single-bore well.
From the top of the reservoir, a single wellbore is first drilled into the reservoir.
From here a lateral is drilled through the side of the well casing, and an additional well section is drilled into the reservoir. Thus, the well has two well sections drain ing the reservoir at the same time. ML (multilateral) is added to the name of the well to indicate that it has several well sections in the reservoir, e.g., HCA-1ML. Further well sections may be added in the same way.
This technology enables production from a larger part of the reservoir, with a smaller number of platform wellheads and at less cost.
Multilateral wells are suitable for conditions in several Danish fields.
The Nini Field
The Nini Field has been developed with two new wells from the Nini A platform, an oil production well, NA-10, and a water-injection well, NA-9, both of which have their reservoir section in the Ty Formation. Both wells were drilled using the drilling rig Mærsk Resolute.
From the new Nini B platform, also known as the Nini East platform, a total of three new wells were drilled during 2009: two new oil production wells, NB-1 and NB-2, and a water-injection well, NB-3, with the Hermod Formation as the reservoir. All the wells were drilled using the drilling rig Mærsk Resolute.
A fatal accident occurred during the completion of well NB-3. This accident is referred to in more detail in the section on work-related injuries in chapter 4, Health and safety.
The Siri Field
The Siri Field was not developed during 2009, but as described in the production section, work is under way to repair the caisson on the Siri platform, where a tempo-rary support structure was established in January 2010; see also the section entitled Inspections in 2009 in chapter 4, Health and safety. In the long term, the plan is to imple-ment a support solution with a three-legged structure, which will stand on the seabed and secure the caisson above the storage tank, thus reducing the caisson’s movements and stopping the formation of cracks. As mentioned in the production section, the permanent solution is expected to be in place in the third quarter of 2010.
The South Arne Field
As part of the third development phase for the South Arne Field, in May 2009 Hess Denmark ApS submitted an application for approval of the first of three stages in the further development of the field. The approval was granted in September and covers a permit to drill and produce from a further two oil production wells, SA-20 and SA-21.
These two wells are an extension of the drainage area on the flanks of the South Arne structure. One is located on the western flank of the main field west of SA-11 in a reservoir of the Tor Formation, while the other is located on the eastern flank of the main field between SA-6 and SA-12 in reservoirs of both the Ekofisk and Tor Formations.
Total production from the two wells is estimated at 1.11 million m³ of oil and 0.33 billion Nm³ of gas.
Some maintenance work has been carried out in the South Arne Field, involving the clean-up of old wells aimed at improving production; see also box 3.1.
The Tyra Field
In October 2009, the operator applied for a permit to drill a new well, TEB-23. The plan was approved in October 2009. The well is to be drilled in a northeastern direc-tion from the Tyra East B platform as a long-reach horizontal well. The well is to be drilled into reservoirs in both the Tyra and the Adda Fields. The well will be drilled using a wellhead module which is available on the Tyra East B platform.
Total production from the well is estimated at 1.2 billion Nm³ of gas and 1.2 million m³ of oil, about 84 per cent from the Tyra Field and about 16 per cent from the Adda Field.
If the TEB-23 well leads to the startup of production from the Adda reservoir, the Adda Field will then be classified as a producing field.
Some of the pipe on the Tyra East platform was replaced during 2009.
Tyra Southeast
As mentioned in the annual report for 2008, the TSEA-3D well was completed and brought on stream in early 2009 as expected.
The Valdemar Field
In October 2009, the operator applied for approval of a plan to further develop the Valdemar Field (the Bo area). This approval was granted in December 2009 and com-prises a permit to drill three new wells using existing wellhead modules. The wells are to be placed on either side of the existing well pattern on the eastern and western flanks of the Bo structure, respectively, in a reservoir of Lower Cretaceous age.
Total production from the three new wells is estimated at 1.7 million m³ of oil and 0.8 billion Nm³ of gas.
The exploration and appraisal wells drilled in 2009 are described in more detail in chapter 1, Licences and exploration.
Information about approved development plans and plans under consideration is also available at the DEA’s website, www.ens.dk.
Fields with no major activity and no approved development plans in 2009 There was no development or other major activity in the following fields in 2009:
Cecilie, Dagmar, Harald, Kraka, Lulita, Regnar, Roar, Rolf, Skjold and Svend.