Securing the Supplies of Fossil Fuels - Energy and Climate: How to Achieve a Successful Energy Transition - page 99

Contrary towhat happens in the case of oil, the recovery yield in the case
of natural gas is comparatively high and therefore cannot be increased
substantially.
However, natural gas has been explored less intensively than oil
and the reserves of natural gas are therefore probably underestimated.
There remains a large exploration potential for discoveries to be
made. The renewal of gas reserves will be achieved in the future main-
ly through new discoveries and the exploitation of unconventional
resources.
Resources of unconventional gas are very large. These resources
include deep deposits, contained in low permeability sedimentary rocks
('tight gas'). Coal bed methane is already widely exploited in the USA
and its production might be greatly increased in other regions of the
world.
Very large quantities of methane are also trapped in the form of
hydrates. Hydrates are solid inclusion compounds, which can be formed
under pressure and at a sufficiently low temperature. Water molecules
form a lattice in which molecules of light hydrocarbons, such as methane,
can be trapped. They form deposits in various cold regions of the world,
near the Arctic zone, in Siberia and in Canada. Hydrates are also trapped
under the bottomof the oceans as a result of the huge pressure due to large
water depths. For the time being, the exploitation of hydrates remains very
limited, due to many difficulties resulting from the need to handle a solid
phase, and also due to the fact that hydrates are often present in a very
dispersed way.
In the future, an increase in energy prices could help to increase explo-
ration efforts, giving access to new reserves of natural gas. It is therefore
premature to consider a short term decline of natural gas production, due
to a depletion of resources.
The advantages of natural gas in environmental terms are quite good,
both at the local and the global level, with a level of CO 2 emissions per unit
of energy output much lower than in the case of coal. It is therefore an
energy well adapted to the transition period, with a much lower environ-
mental impact than coal, especially before the effective deployment of
CO 2 capture and storage technologies.
The comeback of coal
Due to the size of coal reserves and a distribution more favourable for
large countries with high consumption than in the case of hydrocarbons,