The gas exploration company Red Sky Energy has
recently claimed its pilot gas production well north of Whiporie is tapping
into conventional gas reserves in 'tight sands', when only a few months
earlier, they released a report for the Australian Stock Exchange claiming
their exploratory drilling had identified unconventional gas.
I believe the gas industry is deliberately trying to
confuse the community. Firstly they told us that the environmental and social
disasters resulting from shale gas mining in the USA, which was exposed in the
award winning documentary 'Gasland', is different to our local resource which
is coal seam gas.
Natural gas, conventional and unconventional gas,
shale, coal seam and tight sand gas. What does it all mean?
Natural gas is methane, the result of decomposition of
vegetation deposits over millions of years. That methane comes from
conventional and unconventional sources. The conventional source is methane
that has leaked out of the coal seam and become trapped underground in large
reservoirs which can be easily tapped by drilling down into it, and pumping it
out through a limited number of well heads that can operate for many decades.
Unconventional gas is that methane that has either
remained in the coal seam (coal seam gas), or has also seeped out but instead
of accumulating in large reservoirs, has then become trapped in other
underground shale deposits (shale gas) or, as is the case in the Clarence
Valley, in sedimentary sandstone (tight sand gas).
All these unconventional deposits require some level
of “stimulation”, i.e. breaking up the underground rock layers to release the
gas. This is done using relatively new technology that allows horizontal
drilling along the rock seam so that hydraulic fracturing or “fracking” can be
undertaken.
Fracking is the process of pumping a mixture of water,
sand and a variety of chemicals under extreme pressure to smash up the rock
seam. The sand is forced into the cracks to keep them open, and the fracking
process may have to be repeated several times over the life of the well, which
is generally about 15 years.
Because there is a limit to the distance horizontal
drilling can go, an unconventional gas field requires multiple well heads, all
connected by above ground pipelines and roads, and the cracking of the rock
layers increases the risk of disrupting aquifers and polluting underground
water. Methane leaking along the newly formed cracks into the water table, is
what is seeing water bores in Queensland spewing out more gas than water, to
the point where they can be set alight.
Fracking also leads to methane leaking upwards along
those cracks directly into the atmosphere, which are referred to as “fugitive
emissions”, and go largely undetected and are unmeasurable. Methane is a potent
greenhouse gas. So these fugitive emissions are making a significant
contribution to climate change.
Unconventional gas wells are closed down when gas
flows drop to levels that are no longer commercially viable. So after some 15
years of production the well is sealed to prevent the remaining methane from
escaping. However, those fugitive emissions will continue to flow forever, and
the cement casings that line the borehole will all fail over time and also
begin to leak methane. In the USA upwards of 50% of sealed wells were found to
be leaking within 8 years of being abandoned.
- John Edwards
