What is Shale Gas?
Shale Gas is natural gas trapped inside shale rock, composed
mostly of the compound methane. Methane (CH4) is a flammable
hydrocarbon that is the byproduct of organic processes, usually
involving bacterial activity. It is produced in rotting garbage,
swamplands and marshes and even in human digestion.
During two significant geological periods, the Jurassic (146-208
Million years ago) and the Carboniferous (290-363 MYa), global sea
levels were higher than today and much of the then British Isles
were swamped. Prolific plant life grew, died and sank to the floors
of shallow seas and lake beds where mud was also deposited.
Earth in the Jurassic (top) and Carboniferous (bottom) periods.
The British Isles are on the meridian in both maps, near the
equator in the Carboniferous and around 45°N in the Jurassic. Maps
courtesy of Prof. Ron Blakey, Colorado Plateau Geosystems
This organic matter, trapped in the mud, was buried under
successive sediments from later ages and fossilised, the mud
turning into mudstone (shale) and the organic content inside
breaking down into methane under heat and pressure. Thus methane is
trapped inside shale from the Jurassic and Carboniferous periods,
such as the Bowland Shale in Lancashire (Carboniferous) and the
Wealden Shale in the South East (Jurassic)
In conventional reservoirs, gas is found in porous rock with a
"roof" of impermeable rock trapping it. A well is drilled into the
porous rock and the gas flows to the surface. The gas can be
associated or non-associated; associated gas is found with oil and
may need refining to increase the proportion of methane in the
gas.
In contrast to conventional gas, shale is relatively
impermeable, meaning gas cannot easily move through the shale in
which the well is drilled. Hence, in order to recover gas from the
shale it must be "stimulated". The most common and effective method
of doing so is "hydraulic fracturing", or "fracking".
Left to right - an associated conventional well, a shale well, a
non-associated conventional well
Shale gas reserves have been identified in several countries
throughout the world and it is thought that large enough lie
beneath UK soil to contribute significantly to the national gas
reserves.
Processes
