3. Exploration activity: Preamble

Licensing rounds

Licences to explore for oil and gas are allocated by the authorities in what are called licensing rounds. Figure 3.1 shows how the size of the licensing rounds has varied. The first round, in 1965, was by far the largest. After the first oil was found, and the authorities and companies had obtained more knowledge regarding in which areas and at which levels the oil and gas resources could be found, the licensing rounds have become more restricted in area. The authorities have therefore been able to plan the exploration of the Norwegian continental shelf by awarding production licenses in different areas as the resource base has been mapped and the economic and environmental evaluations have been made. The first four licensing rounds only concerned the North Sea. At first, activity was concentrated on the southern part of the Norwegian continental shelf, in the Ekofisk area. The Sleipner and Frigg areas were also included in the second round.

The authorities have also awarded some production licences independently of the licensing rounds, for instance if there has been an urgent need to clarify important resources. An example of this is the Statfjord field which was allocated as a result of a discovery, the Brent field, made in the UK sector of the North Sea. The discovery of the Statfjord field, and subsequently of the Gullfaks field, meant that the focus for exploration shifted to the northern part of the North Sea. In the fourth round, in 1979, a number of production licenses were allocated in this area. This has since proved to be the licensing round which has given the largest oil and gas resources.

After Stortinget (Parliament) gave the go-ahead for exploration north of 62° N, production licences were awarded in the Norwegian Sea and the Barents Sea in the fifth round, in 1980-82. Subsequently, the geographical focus for the rounds has alternated between the three exploration provinces on the Norwegian shelf (Figure 3.2).

Fig. 3.1
Areas and blocks allocated in licensing rounds 1 to 15.

**Fig. 3.2** Number of production licenses per region in each licensing round.
Licensing round	Year	North Sea	Norw. Sea	Barents Sea
1	1965	22
2	1969,71	14
3	1975-77	12
4	1979	8
5	1980-82		5	7
6	1981	8
7	1982		5
8	1984	5	5	5
9	1985	4	3	4
10A	1985	8
10B	1986		8
11	1987	1	5	7
12A	1988	11
12B	1989		6	3
13	1991	12	3	7
14	1993	11	4	2
15	1995	4	14
Outside		12
SUM		132	58	35

Acquisition of seismic data

The most important basis for offshore exploration for oil and gas is seismic data. Acquisition began in the North Sea as early as 1962. Since then, about 4.3 million line kilometres of seismic data have been acquired on the Norwegian continental shelf. Approximately 40% of this originates from areas north of 62° N. As Figure 3.3 shows, an explosive development has taken place in the use of 3D seismic, which is now the sole method used for mapping discoveries and fields and the dominant one in an exploration context.

Fig. 3.4
Exploration wells.

Exploration wells

Since exploration drilling began in 1966, 859 exploration wells have been completed on the Norwegian continental shelf. These comprise 520 wildcat wells and 314 appraisal wells. In addition, there are 25 unsuccessful drillings which, for technical reasons, failed to reach the reservoir level. A total of 1239 development wells have been drilled since production began on the Ekofisk field in 1971. The variation in the number of exploration wells per year is shown in Figure 3.4.

In step with the development of technology and knowledge, exploration has moved to ever-greater depths of water. Figure 3.5 shows how exploration prior to 1975 was chiefly restricted to depths of around 100 m, in the southern part of the Norwegian continental shelf. The exploration well that has been drilled in the deepest water so far is 6607/5-2, drilled by Esso in 1991 (523 m). During 1997-98, exploration drilling will take place at depths down to 1500 m in the Norwegian Sea. A corresponding development has not taken place with regard to the drilling depth (Fig. 3.5). This is because emphasis was placed early in the exploration history on investigating the deeper levels beneath the discoveries that were made, and also reflects the extremely high cost of drilling exploration wells to such great depths.

Exploration and development wells
Definitions and well terms.
Exploration well is a generic term for wildcat and appraisal wells.
A wildcat well is the first well drilled on a new, clearly defined geological structure (a prospect).
An appraisal well is a well which is drilled to determine the extent and size of a discovery.
A development well is a generic term for wells which are used to produce oil and gas from a field. It covers production wells, injection wells and observation wells.
Well designations consist of the following parts:
0000¹/00²-A³-00⁴A⁵ X⁶ T2⁷
¹ quadrant
² block
³ space for exploration well, A, B, C, etc. denote production installations, U for shallow borehole, T for test production well
⁴ serial number in the block
⁵ A, B, C, etc. for sidetracking (new wells), S for exploration well planned to be drilled inclined, R for re-opened exploration well, H for development well completed on the sea floor
⁶ space, 2, 3, 4, etc. for number of times an exploration well is re-opened, X for well abandoned for technical reasons
⁷ well serial number. The first well path is not denoted (space), thereafter T2, T3, etc.
Examples:

31/2-5 Exploration well

31/2-5 SR2 Exploration well which was planned to be drilled inclined and was then re-opened twice or has been temporarily abandoned

30/9-A-25 AX Development well which was sidetracked from 30/9-A-25 and which failed to reach the reservoir

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