Oil reserves the present situation

Hydrocarbon reserves are constituted by oil and gas contained in identified fields, which can be produced under economically and commercially acceptable conditions [76].

They take into account the economic and technical conditions, such as the recovery yield which can be achieved with the available technologies, prevailing at a certain time.

According to the level of certainty with which these reserves are known, it is possible to make the distinction between reserves which are proven

(probability higher than 90 %), probable (probability between 30 % and 90 %) and possible (between 10 % and 30 %).

Resources include quantities which have been identified, but which are not considered commercially exploitable and those which have been assessed as still to be discovered.

Finally, ultimate resources comprise all hydrocarbons present or estimated, including those quantities for which no possibility of extraction has been identified. Ultimate resources include therefore hydrocarbons which cannot be transformed into reserves by using any identified technology. This appraisal can of course change with time.

Unconventional resources are those which cannot be exploited by using standard practices (or 'conventional' means), and are constituted in the case of oil by extra-heavy oils, asphalt sands or oil shale.

With the present technical and economic conditions, proven reserves of oil are estimated at 162 Gt (i.e. 1200 billion barrels), which represents around 40 years of consumption at the present rate.

The diagram in Figure 7.2 represents the different oil resources. The oil production cumulated since the beginning of oil exploitation amounts to 137 Gt. Present proven reserves, with an average oil yield recovery factor of 35%, represent 162 Gt. Fields which remain to be discovered (according to a probabilistic approach based upon the investigation of all the

Figure 7.2 Oil reserves and resources (Source: IFP). Reproduced with permission from Energie & Climat: Réussir la transition énergétique by Alexandre Rojey, Editions Technip, Paris, 2008

sedimentary basins of the planet), if they were exploited with the same recovery yield, represent a further 140 Gt.

Increasing the recovery yield from 35 to 50% (through the use of new technologies) would make it possible to increase present proven reserves by 65 Gt and resources resulting from future discoveries by 60 Gt.

With these assumptions, a total amount of 265 Gt (or 1850 billion barrels), might therefore be added to the present proven oil reserves.

The resources of nonconventional crude oil are huge and amount to 460 Gt, but for the time being only a comparatively small share of these resources may be exploited.

These values can seem reassuring but two important points should not be forgotten. First, the world consumption rate has considerably increased during recent years: more oil has been consumed since 1980 (a period of 26 years) than during the whole previous period (more than a century!). From the supply point of view, the amounts of oil resulting from new discoveries do not correspond to the consumption rate by a long way. Very few giant fields have been discovered in recent years, whereas presently exploited giant fields deliver half of the total world production. Thus, the discovery of the four biggest fields each supplying more than 1 million barrels per year occurred before the 1980s.

Secondly, large uncertainties exist concerning the exact level of proven reserves. The values which are published depend upon the declarations of producing countries which may have an interest in overestimating the level of their reserves.

The uneven geographical distribution of oil reserves creates a geopolitical risk for the security of supplies, which is reinforced by the growing dependence of consuming countries.

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