No, coal is not permeable.
In the article that follows, we’ll explain.
Is Coal Permeable? (EXPLAINED)
There is a commonly held belief that coal is permeable.
Without becoming overly scientific or technical, permeability refers to how well fluids flow through the material.
Water flows through sand pretty quickly and easily, oil takes a bit longer because it’s thicker, hence why water and sand don’t mix very well, and oil and water do.
Coal seems like it would fall somewhere in between, but here’s the kicker, it doesn’t!
Coal is basically made up of carbon compressed over millions of years from decaying organic matter, mostly plants.
Like any rock formation such as limestone or quartzite, which is basically just compressed sand, coal is also composed of countless tiny pockets separated by thin grain boundaries.
These internal weaknesses along with the thin nature of the walls separating each pocket create an ideal condition for fluid to flow through, especially when that fluid happens to be hydrocarbons (oil and gas).
It’s this unique characteristic that makes coal such a great source for extracting both petroleum and methane by fracturing the seams and allowing the gas to flow freely.
This is particularly beneficial when other formations such as sandstone, which also contain natural gases, are too impermeable to allow free-flowing fluid seepage.
As a result, someone with an oil rig can simply drill into a coal seam then use fracking techniques that pump chemical-laced water into the shale to release the trapped gas.
While it’s still a topic of contention in academic circles, this process has been going on for decades without any major problems, until recently.
The Problem with Coal Seam Gas Extraction
In order to extract methane from underground coal seams, chemical-laced water must be pumped into them at very high pressure over long periods of time.
In fact, the Barnett Shale in Texas has been providing natural gas to over five million customers for a period of more than 20 years with no major incidents.
However, this doesn’t mean fracking is completely safe from an environmental standpoint, because all of that chemical-laced water has to go somewhere and usually, it’s right back into the ground.
In more arid areas such as Alberta, Canada, or Queensland, Australia, where there isn’t much excess water available for re-injection, dehydration wells are used instead.
These consist of a series of perforated pipes set vertically several hundred meters underground which extract the methane after purging hydrocarbons and other impurities.
The one advantage of this method is that groundwater pollution risks are virtually eliminated, since only methane is extracted after purging the water.
These ‘dry’ wells are also preferred in more seismically active areas where the risk of structural damage to surrounding homes and buildings would be unacceptable with re-injection methods such as hydraulic fracking.
There is, however, one major problem that accompanies coal seam gas extraction and that is structural deformation or subsidence.
While this isn’t particularly new since it has been known about for decades, problems have surfaced in recent years mainly due to the increased intensity of methane extraction for export markets, most notably Japan.
In order to keep the national market supplied, Japan relies on importing natural gas from countries such as Qatar by tanker ship.
Because Japan has no native reserves of coal seam gas, they rely on Australia to supply enough methane by tanker for over five million homes.
However, in addition to the already sizable carbon footprint associated with natural gas extraction and transportation, there is also a considerable amount of subsidence that occurs when extracting methane from underground coal seams.
The subsidence is in fact created when the pressurized water in the borehole cavitates, which in plain English means it acts like a pump causing surrounding groundwater to wick back into the borehole.
This is what creates the subsidence.
The reality is, this process can’t be prevented because without it you wouldn’t be able to extract any gas at all, since pressure would remain constant instead of dropping off as more fluid was into the ground.
As such, it’s then necessary to carefully monitor the volume of water pumped into the borehole because it will create an unstable situation without careful management.
It was only a matter of time before methane extraction became too much for Queensland, Australia, which is why QGC has reduced operations at its gas wells near Chinchilla by 20% due to concerns over structural damage caused by subsidence.
The Sydney Morning Herald stated an estimated 600 million cubic meters of methane are being extracted from underground coal seams around the town every year, which could probably explain why residents there experience countless earth tremors and feel like they’re living in the shadow of Mount Vesuvius.
The Australian Department of Energy recently released a report on Unconventional Gas Extraction in Australia which outlines the current status of methane extraction from coal seams, shale gas, and tight gas in Australia.
The report also goes a little further in analyzing the risks associated with extracting methane from underground resources given the state of technology at present, which is why politicians have been so keen to push through fracking programs because it would create a lucrative export market for future generations.
Unfortunately, mining methane from coal seams has been going on in Queensland since 1994, which means over 20 years worth of data suggests that when practiced irresponsibly the process can not only cause structural damage to surrounding homes but also trigger seismic activity which could fracture nearby aquifers, resulting in widespread river pollution.
The truth is, there are no regulations governing this type of extraction, even the so-called heavy-handed regulations imposed by the European Union are still considerably less stringent than those governing coal mining.
While many of these problems can be avoided by stopping methane extraction at the source, the problem has only just begun because some nations have plans to actually burn this methane in order to harness its energy potential.
The idea is that gas power plants will run on methane extracted from underground resources rather than transport it all over the world via tanker ships which carry with it an environmental footprint that you wouldn’t believe.
Given Australia’s abundance of natural gas, it would make sense if they stopped exporting methane altogether and instead prioritized transporting it across the country for use in power plants, but of course, this isn’t something the government or industry spokespeople want you to know, so the other option is using methane as a fuel instead of a raw material.
The other idea gaining momentum in Europe is to extract methane from commercial manure and other organic wastes and burn it for energy.
The problem here, however, has more to do with low net calorific values than anything else, since methane derived from manure simply doesn’t pack as much punch as that harvested from natural gas, which means less CO2 emissions per unit of power or heat produced.
Ultimately, coal is classed as a non-permeable rock because its tiny pores are filled with water-soluble minerals and other organic matter that prevent the stone’s natural tendency to allow fluids through.
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