Exploration history and resource growth

02.07.2013

A creaming curve is a diagram used to present the relationship between aggregated or cumulative resource growth from discoveries and wildcats drilled. Its name probably derives from the fact that the biggest discoveries in an area or a play (the cream of the crop) are normally made early in the exploration history of the area or play. As time passes, remaining prospects will be smaller and have a lower discovery probability.

Such a curve presents the exploration history of an area or play. The X axis is linear, with the number of wildcats in the order of their completion. When a well proves resources in a new discovery, the volume found is plotted as a cumulative value on the Y axis. The result is a rising curve which shows how the area or play has been explored. If the curve is steep, a lot of resources have been found or possibly large discoveries made. A gradual curve indicates that proven discoveries have been small or that many dry wells have been drilled.

 

Exploration history and resource growth on the NCS

The first well on the NCS, 8/3-1 in the south-eastern part of Norway’s North Sea sector, was spudded in 1966. Since then, some 895 wildcats have been drilled and provide the data set for the creaming curve. Wildcats terminated, primarily for technical reasons, before reaching their target are not included.

About 615 wildcats have been drilled in the North Sea, 200 in the Norwegian Sea and roughly 80 in the Barents Sea. The first wildcats in the Norwegian and Barents Sea were spudded in 1980.

The creaming curve shows that discoveries were made after a few wells in all three areas (figure 5.1).

 

Figure 5.1 Proven and undiscovered resources (light colours) in the North (blue), Norwegian (red) and Barents (purple) Seas. The creaming curve also includes discoveries in resource class 6, which are not included in the resource account.

 

While the first discovery in the North Sea, 25/11-1 Balder, was proven by the second well on the NCS, it took 32 years to bring it on stream. The first big find was made in 1969 with the 27th wildcat, 2/4-2 Ekofisk. This discovery was on stream as early as two years later, when test production began.

The first discovery in the Norwegian Sea, 6507/11-1 Midgard, was proven with the third wildcat in 1981. This forms part of the Åsgard field, which came on stream in 1999.

In the Barents Sea, the first discovery was again made by the third wildcat, 7120/8-1 Askeladd. It came on stream in 2007 as part of the Snøhvit field.

Resources proven in the North Sea are four times greater than those in the Norwegian Sea and 14 times larger than in the Barents Sea. In addition to the creaming curve and proven resources for each area, figure 5.1 presents the uncertainty range for the undiscovered resources. The latter are estimated on the basis of current knowledge about the areas, and the figure will probably change with new information. Based on current knowledge, the combined resources in the Norwegian and Barents Seas will be smaller than those in the North Sea. To provide the most accurate possible exploration history, all discoveries are included in the database – including those in resource category 6 (see the fact box).

Creaming curves have been developed for each part of the NCS, broken down between liquids and gas, and for individual plays in each area. These plays still have an undiscovered potential, and a number of them have a long exploration history – particularly in the North Sea.

 

Exploration history and resource growth in the Barents Sea

Some 390 billion scm of gas and 210 million scm of liquids had been proven in the Barents Sea at 31 December 2012 (figure 5.2). The biggest gas discovery is 7121/4-1 Snøhvit in 1984. This includes NGL and condensate as well, which are shown in the curve for liquids. The Snøhvit gas field also comprises four discoveries made prior to 7121/4-1 Snøhvit. These are shown as a small rise in the curve after three wells.

 

Proven and undiscovered (light colours) liquid and gas resources in the Barents Sea


Figure 5.2
Proven and undiscovered (light colours) liquid and gas resources in the Barents Sea.

 

Figure 5.2 shows that possibilities for finding more liquids and gas are considerable. This is illustrated in the columns by the lighter colour shades. A big uncertainty range indicates that knowledge of the Barents Sea remains limited, particularly its northern part. The curves for both liquids and gas show that discoveries have been made in a number of the recent wells. These finds have led to great interest in the area. The plays discussed are illustrated in figure 5.3.

 

Extent of the plays discussed in the Barents Sea.

Figure 5.3 Extent of the plays discussed in the Barents Sea.

 


Upper Triassic to Middle Jurassic play in the Hammerfest Basin

The Upper Triassic to Middle Jurassic play in the Hammerfest Basin is the most thoroughly explored Barents Sea play. This is where the biggest gas discovery, 7121/4-1 Snøhvit, was made. The play also embraces the Goliat oil field, currently under development. Drilling began in this area in 1980. There have been periods with few wells and small discoveries, particularly in the 1990s. Petroleum activities in the Barents Sea were temporarily suspended for a couple of years soon after 2000. The estimate of undiscovered resources shows that the play is still expected to have an interesting potential. See figure 5.4.

 

Total resources, proven and undiscovered (light blue), in the Upper Triassic to Middle Jurassic play in the Hammerfest Basin. 

Figure 5.4 Total resources, proven and undiscovered (light blue), in the Upper Triassic to Middle Jurassic play in the Hammerfest Basin.

 


Lower to Upper Triassic play on the Bjarmeland Platform

Little exploration has taken place in the Lower to Upper Triassic play on the Bjarmeland Platform. Some 10 wildcats have been drilled and three gas discoveries made, with 7225/3-1 (Norvarg) as the largest. See figure 5.5. The first well to test the play was drilled in 1987, and the next five were dry. An appraisal well is to be drilled on the 7225/3-1 discovery this year. After a couple of discoveries which were significantly smaller than expected, 7225/3-1 (Norvarg) is encouraging, and the estimate of undiscovered resources shows that the potential remains large.

 

Total resources, proven and undiscovered (light blue), in the Lower to Upper Triassic play on the Bjarmeland Platform.

Figure 5.5 Total resources, proven and undiscovered (light blue), in the Lower to Upper Triassic play on the Bjarmeland Platform.

 

Upper Triassic to Lower Cretaceous plays along the Ringvassøya-Loppa and Bjørnøyrenne fault complex

The Upper Triassic to Lower Cretaceous plays along the Ringvassøya- Loppa and Bjørnøyrenne fault complex are relatively unexplored, with about 16 wildcats. More than half of these were dry. See figure 5.6. The first well in these plays was drilled in 1983, and the first discovery there – the 7019/1-1 gas find – lies right at their southern end. Finding oil in Johan Castberg (7220/8-1 Skrugard and 7220/7-1 Havis) has prompted a new view of the plays, and interest in exploring them is great. The estimate for undiscovered resources shows that the potential remains large.

 

Total resources, proven and undiscovered (light blue), in the Upper Triassic to Lower Cretaceous plays along the Ringvassøya-Loppa and Bjørnøyrenne fault complex.

Figure 5.6 Total resources, proven and undiscovered (light blue), in the Upper Triassic to Lower Cretaceous plays along the Ringvassøya-Loppa and Bjørnøyrenne fault complex.

 

 

Exploration history and resource growth in the Norwegian Sea

Some 1 000 billion scm of gas and 975 million scm of liquids had been proven in the Norwegian Sea at 31 December 2012. See figure 5.7. Ormen Lange is the biggest gas discovery. The creaming curve shows that the first discovery wells found mainly gas as well as a good deal of oil. In an early phase of its exploration history, the Norwegian Sea was considered to be a gas province. The discovery of Draugen changed that assessment. Wells up to Norne proved relatively large liquid resources, but the curve subsequently shows smaller growth. Ormen Lange caused the curves for liquids and gas to move closer together, following about 12 years of exploration drilling which largely discovered liquids. The most recent wildcats, roughly 30 in all, have largely proven gas, so that the gas curve lies a little above that for liquids. The estimate of undiscovered resources shows that the upside potential for gas is considered to be rather larger than for liquids, that uncertainty is high but lower than in the Barents Sea, and that the potential remains large. The plays discussed are presented in figure 5.8

 

Proven and undiscovered (light colours) liquid and gas resources in the Norwegian Sea.


Figure 5.7 Proven and undiscovered (light colours) liquid and gas resources in the Norwegian Sea.

 

Extent of the plays discussed in the Norwegian Sea.

Figure 5.8 Extent of the plays discussed in the Norwegian Sea.

 

 

Upper Triassic to Middle Jurassic play on the Halten Terrace- Nordland Ridge

The creaming curve for the Upper Triassic to Middle Jurassic play on the Halten Terrace-Nordland Ridge and nearby structural elements shows that this is the best explored and most successful play in the Norwegian Sea so far. See figure 5.9. Exploration began in 1981, and the 6507/11-1 Midgard discovery was made after a few wells. With the exception of the Draugen oil field and the Ormen Lange gas field, all the largest discoveries in the Norwegian Sea have been made in this play. Finds since 2000 have been relatively small, but the play is still considered to have a substantial potential.

 

Total resources, proven and undiscovered (light blue), in the Upper Triassic to Middle Jurassic play on the Halten Terrace-Nordland Ridge.

Figure 5.9 Total resources, proven and undiscovered (light blue), in the Upper Triassic to Middle Jurassic play on the Halten Terrace-Nordland Ridge.

 

 

Upper Cretaceous to Upper Palaeocene plays in deep water

The Upper Cretaceous to Upper Palaeocene plays in deepwater areas of the Norwegian Sea have been explored since 1997, with Ormen Lange as the biggest discovery so far. See figure 5.10. The first gas find is 6707/10-1 (Luva), which has been sanctioned for development together with several smaller discoveries as part of the Aasta Hansteen development. These discoveries are illustrated as a slight rise in the creaming curve between 2008 and 2009. The most recent deepwater well was drilled in 2011, and no wells are planned for 2013. Expectations for these plays were great when exploration began in 1997, but results so far have been less encouraging. However, the play still has a large potential. 

 

Total resources, proven and undiscovered (light blue), in the Upper Cretaceous to Upper Palaeocene plays in deep water.

Figure 5.10 Total resources, proven and undiscovered (light blue), in the Upper Cretaceous to Upper Palaeocene plays in deep water.

 


Exploration history and resource growth in the North Sea

Some 3 000 billion scm of gas and 5 100 million scm of liquids had been proven in the North Sea at 31 December 2012. See figure 5.11. Statfjord and Ekofisk are the biggest oil fields, and by far the largest gas field is Troll East. After Grane was discovered in 1991, the curve for liquids rose weakly until 16/2-6 Johan Sverdrup was found in 2010. The curve for gas shows a weak rise after the discovery of Kvitebjørn in 1994. The estimate for undiscovered resources in the North Sea is less uncertain than for the Norwegian and Barents Seas because this area has been more thoroughly explored. Over three times as many wildcats have been drilled there than in the Norwegian Sea, and about eight times more than in the Barents Sea. Opportunities for making interesting discoveries in the North Sea are still present. The plays discussed are presented in figure 5.12.

 

Proven and undiscovered (light colours) liquid and gas resources in the North Sea.


Figure 5.11
Proven and undiscovered (light colours) liquid and gas resources in the North Sea.

 

The extent of the plays discussed in the North Sea.

Figure 5.12 The extent of the plays discussed in the North Sea.

 

Upper Triassic to Middle Jurassic play in the central and northern North Sea sector

The Upper Triassic to Middle Jurassic play in the central and northern areas of Norway’s North Sea sector is the best explored on the NCS, and many of the biggest finds lie there. Most of these are on the Tampen Spur. The biggest discoveries were proven before 1980, and no large finds have been made in this play since Kvitebjørn in 1994. See figure 5.13. However, small discoveries are frequently proven, which is illustrated in the curve by a steady rise. One of the largest finds since 2010 is 35/9-6 (Titan). Although very considerable resources have been proven in this play, it still has a significant potential.

 

Total resources, proven and undiscovered (light blue), in the Upper Triassic to Middle Jurassic play in the central and northern North Sea sector. 

Figure 5.13 Total resources, proven and undiscovered (light blue), in the Upper Triassic to Middle Jurassic play in the central and northern North Sea sector.

 

Upper Jurassic play in the northern North Sea sector

The Upper Jurassic play in the northern part of Norway’s North Sea sector contains the Troll field, as shown in figure 5.14. This giant find means that the other discoveries in the play barely show up on the curve when Troll is included. A creaming curve has accordingly also been produced without Troll. See figure 5.15. The curves show that relatively few discoveries have been made or resources proven when Troll is excluded. Few wells were drilled in the five-year periods 1975-79, 1986-90, 1991-95 and 2003-07. Since 2007, exploration activity has revived, and the 35/9-7 (Skarfjell) discovery was proven in 2012. This play retains an interesting potential for undiscovered resources.

 

Total resources, proven and undiscovered (light blue), in the Upper Jurassic play in the northern North Sea sector.

Figure 5.14 Total resources, proven and undiscovered (light blue), in the Upper Jurassic play in the northern North Sea sector.

 

 

Total resources, proven and undiscovered (light blue), in the Upper Jurassic play in the northern North Sea sector after excluding Troll.

Figure 5.15 Total resources, proven and undiscovered (light blue), in the Upper Jurassic play in the northern North Sea sector after excluding Troll.

 

 

Upper Jurassic play in the southern North Sea

The Upper Jurassic play in the southern part of Norway’s North Sea sector has a long exploration history. See figure 5.16. Discovered in 1976, the Ula oil field came on stream in 1986. The creaming curve shows that relatively few resources were found from the discovery of Tambar in 1983 to 8/10-4 S (Butch) in 2011 and 2/4-21 (King Lear) in 2012. This play is still expected to have a substantial potential.

 

Total resources, proven and undiscovered (light blue), in the Upper Jurassic play in the southern North Sea sector.

Figure 5.16 Total resources, proven and undiscovered (light blue), in the Upper Jurassic play in the southern North Sea sector.

 

Palaeocene play in the central North Sea sector

The Palaeocene play in the central part of Norway’s North Sea sector has a long exploration history. See figure 5.17. Since the Balder oil field was proven in 1967, about 100 wildcats have been drilled in the play. Relatively few resources were found between the discovery of Jotun in 1994 and the Alvheim find in 1998. Four discoveries were made in 2003, of which 25/4-7 (Kneler) and 24/6-4 (Boa) are part of the Alvheim field. The other two are 16/6-1 (Verdandi) and the 25/4-9 S Vilje oil field. A discovery was also made in production well 25/8-C-20 on Balder. Proven in 2008, 25/11-25 Svalin is now under development. Some 10 wildcats have been drilled since 2008, but with few resources proven. The potential for finding more is present.

 

Total resources, proven and undiscovered (light blue), in the Palaeocene play in the central North Sea sector.

Figure 5.17 Total resources, proven and undiscovered (light blue), in the Palaeocene play in the central North Sea sector.