Undiscovered resources

Resrapp2016engelsk-ingress
04.05.2016
The updated estimate for undiscovered resources confirms that total remaining resources provide the basis for oil and gas production over many decades to come. It is roughly the same as the previous estimate in 2013.

Total undiscovered resources are estimated to be 2 920 million scm oe. About half of this is expected to be in the Barents Sea, where the biggest change has occurred in the estimate. It has increased by about 125 million scm oe for this area.

Undiscovered resources are estimated to lie between 1 350 (P95) and 5 490 (P5) million scm oe (figure 3.1). This calculation covers the whole NCS with the exception of Barents Sea North- East (BSNE). See figure 3.2.

The estimates for undiscovered resources are very uncertain. That reflects the difference between the high (P5) and low (P95) assessments. Uncertainty is greatest in areas with limited information and a short exploration history, such as large parts of the Barents Sea. It is considerably smaller in the North Sea and the well-explored parts of the Norwegian Sea (figures 3.1 and 3.2).

 Figure 3.1 Recoverable undiscovered resources in total and for each part of the NCS. The expected value is specified in the columns.

Figure 3.1 Recoverable undiscovered resources in total and for each part of the NCS. The expected value is specified in the columns.

 

Figure 3.2 Recoverable undiscovered resources for each part of the NCS, broken down by liquid and gas. The expected value is specified in the columns. 

Figure 3.2 Recoverable undiscovered resources for each part of the NCS, broken down by liquid and gas. The expected value is specified in the columns.

 

Liquid is expected to account for about half the total undiscovered resources (figure 3.3). The estimate for liquid is highest in the Barents Sea and lowest in the Norwegian Sea. Where gas resources are concerned, the estimate is significantly higher in the Barents Sea than in the other parts of the NCS (figures 3.2 and 3.4).

 

Figur 3.3 Recoverable undiscovered resources in total, broken down by liquids and gas. The expected value is specified in the columns.

Figur 3.3 Recoverable undiscovered resources in total, broken down by liquids and gas. The expected value is specified in the columns.

 

Figure 3.4 Recoverable undiscovered resources for each part of the NCS, broken down by liquid, gas and total resources.

Figure 3.4 Recoverable undiscovered resources for each part of the NCS, broken down by liquid, gas and total resources.

 

Almost half the total undiscovered resources are expected to be proven in the Barents Sea, with the remainder divided roughly equally between the North and Norwegian Seas.

The Barents Sea contains 70 per cent of expected undiscovered resources in Triassic and older plays (figure 3.5). The Upper Triassic is included in Lower to Middle Jurassic plays in the North and Norwegian Seas, but contributes a smaller share of their resources. Plays older than the Late Triassic account for less than two-three per cent of total expected resources in the North and Norwegian Seas.

 

Figure 3.5 Recoverable undiscovered resources for each part of the NCS by geological stratigraphic level.

Figure 3.5 Recoverable undiscovered resources for each part of the NCS by geological stratigraphic level.

 

About 80 per cent of the undiscovered resources in the North Sea are expected to be in Upper Triassic and Jurassic plays, while the corresponding figure for the Norwegian Sea is about 55 per cent. Jurassic plays account for 24 per cent of total undiscovered resources in the Barents Sea. Cretaceous and Cenozoic plays contribute six, 41 and 17 per cent of total undiscovered resources in the Barents, Norwegian and North Seas respectively (Cretaceous plays in the North Sea include chalk reservoir rocks). This reflects differing geological developments in the three regions.

 

Changes from the 2013 analysis

The estimate for undiscovered resources at 31 December 2015 shows only minor changes from 31 December 2013. The expected value has been reduced slightly from 2 940 to 2 920 million scm oe (figure 3.6).

 

Figure 3.6 Comparison between total recoverable undiscovered resources in the 2013 and 2015 analyses.

Figure 3.6 Comparison between total recoverable undiscovered resources in the 2013 and 2015 analyses.

 

Liquid

The estimate for liquid has hardly changed from 2013 to 2015, with the expected value reduced by one per cent from 1 450 to 1 435 million scm (figure 3.7).

 

Figure 3.7 Comparison of the distribution of recoverable undiscovered liquid resources for each region and the whole NCS (2013 and 2015 analyses).

Figure 3.7 Comparison of the distribution of recoverable undiscovered liquid resources for each region and the whole NCS (2013 and 2015 analyses).

 

Some 30 million scm of liquid have been discovered in the North Sea since 2013. The estimate for liquid has been reduced from about 565 to 495 million scm. Exploration results in recent years which indicate a smaller quantity of liquid than previously estimated are the most important reason for this change, which relates primarily to plays with Palaeocene, Lower Cretaceous and Upper Jurassic reservoirs.

About 35 million scm of liquid have been found in the Norwegian Sea since 2013. The estimate for liquid has been cut by roughly 2.5 per cent from about 375 to 365 million scm. According to the new estimates, liquid is reduced by some 50 million scm for a number of the plays. However, exploration results in recent years and new information have contributed to an upward adjustment of expectations for Upper Jurassic plays. That primarily reflects a reassessment of their potential as a result of such discoveries as 6406/12-3 S (Pil) and 6406/12-3 A (Bue) (figure 3.8).

 

Figure 3.8 Plays in the Norwegian Sea with the biggest changes in undiscovered resources.

Figure 3.8 Plays in the Norwegian Sea with the biggest changes in undiscovered resources.

 

The estimate for the Barents Sea has been raised by about 13 per cent, from 510 to 570 million scm, primarily as a result of the 7220/11-1 (Alta) discovery. That confirmed the play from Carboniferous to Permian on the Loppa High, and thereby contributed to a sharp increase in its estimated resources (figure 3.9). The well also proved both oil and gas, which helped to strengthen expectations of multiphase discoveries in the area. Exploration history in recent years has also raised expectations of making such finds in more plays than earlier expected.

 

Figure 3.9 Carboniferous to Permian plays in the Barents Sea with the biggest changes in undiscovered resources.

Figure 3.9 Carboniferous to Permian plays in the Barents Sea with the biggest changes in undiscovered resources.

 

Gas

Undiscovered gas resources on the NCS are estimated to be 1 485 billion scm, down by 0.3 per cent from 1 490 billion (figure 3.10).

 

Figure 3.10 Comparison of distribution of recoverable undiscovered gas resources for each region and the whole NCS (2013 and 2015 analyses).

Figure 3.10 Comparison of distribution of recoverable undiscovered gas resources for each region and the whole NCS (2013 and 2015 analyses).

 

No change has been made to the estimate for the North Sea. According to the new analysis, the expectation of finding gas has increased somewhat for plays with Upper Triassic to Middle Jurassic reservoirs. This is because the exploration history of recent years indicates that future discoveries will contain more gas than suggested in earlier estimates. The gas estimate has been reduced to some extent for Palaeocene and Upper Jurassic plays because few discoveries have been made in these and proven deposits are small. Viewed overall, therefore, the expectation for gas in the North Sea is unchanged.

The estimate for the Norwegian Sea is down by about 14 per cent, from 475 to 410 billion scm. Some 30 billion scm of gas has been proven since the previous analysis. The new assessment cuts the gas potential for half the plays by up to 100 billion scm. Downgrading the sub-basalt and Palaeocene plays in deep water and the Upper Cretaceous play by the Træna Basin provides the biggest reductions (figure 3.8). This is offset to some extent by an increase in a couple of plays – particularly the Upper Jurassic – which also account for the biggest increase of liquid.

In the Barents Sea, the estimate has risen by some eight per cent from 765 to 825 billion scm. This reflects exploration results in recent years, including the 7220/11-1 (Alta) discovery, and new evaluations related to the 23rd licensing round.

 

Historical changes

The NPD regularly publishes new figures for undiscovered resources on the NCS. Using the same methodology since the mid-1990s provides a good basis for comparing the estimates. From 1996 to 2015, this comparison shows an increase up to 2002 followed by a decline to 2010 (figure 3.11).

 

Figure 3.11 Total recoverable undiscovered resources over time for each part of the NCS.

Figure 3.11 Total recoverable undiscovered resources over time for each part of the NCS.

 

The downturn from 2003 largely reflected a reduction in estimates for a number of Norwegian Sea plays, particularly their gas potential.

In 2010, the reduction was primarily attributable to downgraded expectations of gas discoveries in both the North and the Norwegian Seas. One of the reasons in the latter area was changed expectations of the potential off Lofoten, Vesterålen and Senja following the NPD assessment published in 2010. In addition, exploration results reduced expectations for deepwater plays.

Barents Sea South-East and the waters around Jan Mayen were included in the estimates for the Barents and Norwegian Seas respectively from 2012. That boosted the estimate for total undiscovered resources.

The proportion of gas has increased in the North Sea since 2012. Little change has occurred in the relationship between liquid and gas in the Norwegian and Barents Seas (figure 3.12).

 

Figure 3.12 Liquid versus gas in the estimates of 2012, 2013 and 2015 for each part of the NCS.

Figure 3.12 Liquid versus gas in the estimates of 2012, 2013 and 2015 for each part of the NCS.

 

Methodology

Several methods are available for estimating how much oil and gas might have been deposited and generated in an area. The choice of methodology depends on how much is known about the area. Play analysis is the approach used by the NPD.

Whether a play contains petroleum is uncertain until a discovery has been made. If producible petroleum has not been proven in a play, it is unconfirmed. Uncertainty prevails in such plays over one or more of the geological factors which must be present for petroleum to be proven. A confirmed play is characterised by a discovery which has proven producible petroleum. This does not need to be commercial.

The NPD has defined and analysed 74 plays, of which 44 have been confirmed by discoveries (table 3.1).

 

Table 3.1 Plays by region and status.

Table 3.1 Plays by region and status.

 

Estimating a single play

The following variables form the basis for estimating the undiscovered resources in a single play.

Area of the play

  • The play has a delineated area.

Number of prospects per unit area

  • The estimated number of prospects is based on an assessment of their density in one or more calibration areas where all relevant elements can be counted. These elements are the number of discoveries, dry wells, mapped prospects, leads and the number of postulated prospects (which could be mapped in the future).

Size of future discoveries

  • Estimates of the size of possible future discoveries from postulated prospects and leads generally build on the magnitude of mapped prospects in the play. Information from discoveries is important for confirmed plays. Data from relevant plays will be very significant for all plays, while information from analogues is also important for less explored cases. Calculating the size of future discoveries builds on estimates of volume and fluid (liquid and gas) parameters. Where the various volume parameters are concerned, the estimate for gross rock volume will be the most significant for calculating resources in the prospect. Correlations between volume and fluid parameters are incorporated in order to describe the relationship between the various parameters.

Probability of success

  • The probability of making future discoveries comprises the probabilities of a play being confirmed (play probability) and of a prospect becoming a discovery if the play is confirmed. The historical finding rate for this and comparable plays is an important input when estimating the probability of success.

Probability of phase petroleum

  • Evaluations of source rock and migration are used to assess the probability of proving oil, gas or a combination of both (multiphase discovery). Information from relevant discoveries is also important for such assessments.

A stochastic calculation method based on the variables described above is used by the NPD to estimate the total resources in each play. All the variables are specified with a probability distribution, except probabilities of success and phase petroleum. The variables and the correlations between certain volume and fluid parameters across deposits provide estimates for resources within each play.

Correlations between parameters and between deposits are of significance for the resource distribution’s range. A positive correlation increases the range for the total resource estimates. Total resources in a play represent the sum of the postulated prospects, leads and mapped prospects when the probability of success has been taken into account.

 

Estimate for each part of the NCS

The NPD uses a stochastic calculation method to estimate resources in the North, Norwegian and Barents Seas. Input data for the calculations are as follows.

  • The resource distribution for all plays in that part of the NCS. Each of these regions contains a number of plays (table 3.1).
  • Interdependencies between play probabilities in unconfirmed plays. In frontier areas, for example, several plays could be interdependent in terms of the presence of source rocks. Should a well confirm one play, the probability for other plays with the same source rock will increase.
  • Correlations between volume and fluid parameters across plays.

Interdependencies and correlations between plays are of significance for the range of the resource distribution in the various parts of the NCS. Expected resources for one area are equal to the sum of expectations for each play. The resource estimate range is greater for an area with interdependencies and positive volume correlations than for ones with few or no interdependencies or volume correlations between plays.

 

Estimate for the whole NCS

A stochastic calculation method is used by the NPD to estimate the total undiscovered resources on the basis of the plays across the whole NCS. The estimated expected value for total undiscovered resources is equal to the sum of expectations for each region. The range in the total estimate is the result of the range for each part and of the interdependencies in probabilities of success and correlations across the parts of the NCS.

 

Definitions
Undiscovered resources: The quantities of petroleum which are estimated at a given time to be recoverable from deposits yet to be proven by drilling.

Play: A geographically delineated area where several geological factors are present so that producible petroleum could be proven.

These factors are:

1) reservoir rock: a porous rock where petroleum can accumulate. Reservoir rocks in a specific play will belong to a given stratigraphic level.

2) cap rock: a tight (impermeable) rock overlaying a reservoir rock, so that petroleum can migrate no further and accumulates in the reservoir. The resulting trap must have formed before petroleum ceased to migrate into the reservoir.

3) source rock: shale, limestone or coal containing organic materials which can be converted into petroleum. The source rock must also be mature – in other words, have a temperature and pressure such that petroleum actually forms – and the petroleum must be able to migrate from source rock to reservoir rock. A play is confirmed when producible petroleum is proven in it. This discovery does not have to be commercial. If no producible petroleum has yet been proven in a play, it is unconfirmed.

Play probability: The estimated probability that producible petroleum can actually be proven in a play. This probability is estimated with the aid of a geological assessment of the probability that reservoir, source and cap rocks are present in the play.
Prospect: A possible petroleum deposit with a mappable, delineated volume of rock.
Probability of success: Describes the possibility of proving petroleum in a prospect by drilling. It is the product of the probability that the play exists, the presence of a reservoir and a trap, migration of petroleum into the trap and the containment of petroleum in the trap (see play).
Lead: A possible petroleum trap where available data coverage and quality are not sufficient to map or delineate the rock volume.

Uncertainty: Expresses the range of possible outcomes or results. This can be described in many ways, most often with the aid of high or low estimates (the NPD estimates, for example, that 1 350-5 490 million scm oe of total recoverable undiscovered resources remain to be identified on the NCS).

Uncertainty is usually calculated using statistical methods, such as Monte Carlo simulations. High and low uncertainties can then be described with the aid of statistical concepts. Where undiscovered resources are concerned, the NPD generally uses P95 for the low estimate. This means that, given the assumptions applied in the analysis, the probability of a result equal to or larger than the P95 value is 95 per cent. P5 is used for the high estimate, which means a five per cent probability that the result will be equal to or larger than the P5 value.

Expected value: The average value. This is generally defined as the arithmetic mean of all the outcomes in the statistical distribution. It is much used, and has the property that the expected value for various distributions can be summed to give a sum of distributions.

Illustation