Securing the Supplies of Fossil Fuels - Energy and Climate: How to Achieve a Successful Energy Transition - page 92

(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 esti-
mated, 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 tech-
nology. 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 162Gt (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
137Gt. Present proven reserves, with an average oil yield recovery factor
of 35%, represent 162Gt. Fields which remain to be discovered (accord-
ing to a probabilistic approach based upon the investigation of all the

Figure 7.2 Oil reserves and resources ( Source : IFP). Reproduced with permission

Energie & Climat: Reussir la transition energetique

from by Alexandre Rojey,

´ ditions Technip, Paris, 2008