GAS STORAGE
3 PRODUCTION AND DEVELOPMENT
production during the year, or vice versa. Appendix B (field data) indicates the number of active wells at the end of 2009.
Appendix A shows figures for the production of oil and gas from the individual fields.
Gas production is broken down into sales gas, injection gas, fuel gas and flared gas.
Moreover, appendix A contains figures for the production and injection of water as well as for CO2 emissions.
Fig. 3.2 Location of production facilities in the North Sea 2009
Gorm Lulita
South Arne
Roar
Rolf
Tyra
Skjold
Regnar Kraka
Dan Valdemar
Siri
20 km
65 km
Gas (80 km)
Gas (235 km)
Svend Gas (29 km) Gas (260 km)
Halfdan NE 32 km
16 km
19 km 33 km
26 km Tyra SE
Nini A
Cecilie 13 km
27 km
7 km Nini B
Dagmar Harald
Halfdan Trym
Gas (29 km)
6 15'0
Oil field Gas field
Pipelines owned by DONG Oil pipeline
Gas pipeline Multiphase pipeline
Pipeline owned 50/50 by DONG and the DUC companies Planned multiphase pipeline
to Fredericia to Nybro to Nybro
Oil (330 km)
to NOGAT
Annual production figures since production started in 1972 are available at the DEA’s website, www.ens.dk.
Oil production
Oil production in 2009 totalled 15.2 million m³, a 9.0 per cent decline compared to 2008.
In addition to the expected fall in total Danish production, some of this downturn is due to the shutdown of several fields for shorter or longer periods of time in con-nection with maintenance, repairs, modifications or, as regards the Siri platform, the identification of cracks in the wellhead caisson support structure.
Because of these cracks, production from the Siri platform was shut down from 1 September 2009 until mid-January 2010; see also the section entitled Inspections in 2009 in chapter 4, Health and safety. In connection with a routine inspection of the storage tank, cracks were identified in the part of the structure that supports the caisson. The caisson is a protective section of pipe which encases all the Siri Field’s production pipe from a couple of metres above the seabed up to the platform. At year-end, work was still under way on a seabed support solution. A temporary solu-tion was in place in January 2010, enabling producsolu-tion from the field to resume.
A permanent solution is expected to be ready during the third quarter of 2010.
The shutdown of the Siri platform resulted in the suspension of production not only from the Siri Field, but also from the Cecilie and Nini Fields, as production from these fields is sent to the Siri platform.
On other installations, improved production has been achieved in certain old wells following the completion of clean-up and refurbishment programmes.
Figure 3.4 shows the historical development in production over the past 25 years.
Gas production
Natural gas production totalled 8.6 billion Nm³ of gas in 2009, with sales gas account-ing for 7.3 billion Nm³. By sales gas is meant the portion of the gas suitable for sale.
Production dropped by 13.1 per cent compared to 2008.
0
Fig. 3.3 Breakdown of oil production by company
Fig. 3.4 Production of oil and sales gas 1985-2009
Oil production, million m3 Gas production, sales gas, billion Nm3 20
Figure 3.4 shows the historical development in sales gas production over the past 25 years. Annual production figures since production started in 1972 are available at the DEA’s website, www.ens.dk.
Gas injection in the Tyra Field rose by approximately 75 per cent in 2009 compared with 2008. This proportionally large increase must be viewed in light of the very low injection in 2008. Gas exports were also significantly lower than in 2008. However, gas injection in the Siri Field dropped by about 75 per cent, largely due to the shutdown of the Siri Field during the last four months of 2009.
The unsold part of the gas produced is used primarily as fuel as part of the energy supply to the platforms. A small volume of gas is flared for technical and safety reasons. The volumes of gas consumed as fuel and flared are described in chapter 5, Environment and climate, and in appendix A.
Water production and water injection
Water is produced as a by-product in connection with the production of oil and gas.
The water can originate from natural water zones in the subsoil or from the water injection that is carried out in order to enhance oil production.
In Denmark, 37.5 million m³ of water was produced and 44.4 million m³ of water was injected during 2009, of which around a third was reinjected production water, while the remainder was treated seawater. The injection of water has fallen by 12.9 per cent since 2008, while the quantity of produced water has decreased by 5.3 per cent compared with 2008, when water production peaked.
The use of water injection
During the initial production phase of a new field, there is a substantial pressure dif-ference between the reservoir and the surface. The excess pressure in the reservoir enables the oil to be produced through natural drainage for a certain period of time.
As the oil is produced, the pressure in the reservoir will fall. Injecting water into the reservoir maintains the pressure, and the oil is displaced as it flows towards the pro-duction wells. Flushing the reservoir with injection water can also benefit propro-duction to some extent, depending on the chemical composition of the water.
Oil production Water production Water injection
73 75 77 79 81 83 85 87 89 91 93 95 97 99 01 03 05 07 09 0
5 10 15 20 25 30 35 40 45 50 m. m3
Fig. 3.5 Production and injection in Danish fields with water injection
Injection takes place through wells, which correspond to production wells. These wells must be located optimally relative to the production wells. In fields with low reservoir thickness, such as the Danish fields, horizontal production and injection wells are dril led alternately in a parallel pattern across the reservoir. This type of pattern can clearly be seen in the main Halfdan Field and on the northwestern flank of the Dan Field. In these production/injection patterns, it is important that the outermost well is always a pro-duction well to ensure that oil is not forced away from the propro-duction wells.
In Denmark, the first injection well was drilled in the Skjold Field in 1986. Since then, the technique has been developed in eight fields with a total of 106 active water-injection wells in 2009. Figure 3.5 shows the relationship between produced and injected quantities in the eight Danish fields that use water injection. The figure shows that oil production is accompanied by large volumes of produced water. The volume of injected water is decreasing, and in 2009 it corresponded approximately to the volume of produced water.
The quality and chemical composition of the water injected must not cause unneces-sary wear on the materials and equipment in the wells. For example, seawater cannot be used directly because of its oxygen content, which corrodes iron.
The water that is produced contains oil residues and geological material, among other things. It must therefore be treated before reinjection. Alternatively, treated seawater can be used. In case of some fields, this water is supplied from another processing plant, e.g. from Dan to the Halfdan Field. Efforts are being made to optimize the pro-cesses concerning produced water and injection water, allowing a greater proportion of the produced water to be reinjected. This will reduce the discharge of oil residues into the sea; see also the section entitled Marine discharges in chapter 5, Environment and climate.