Using oil and gas as an energy source is a remnant of old Industial Age technology and not normally part of our discussion of the developing Global Age. However, the increased price of fossil fuels, resulting from the world's diminishing oil supply, has led to some extraordinary techniques being used to extract oil and gas from 'unconventional' sources. These techniques seem to have been shrouded in confusing jargon and emotional claims.
In this post, I have attempted to set out my understanding of techniques such as fracking and coal seam gas extraction in plain language.
Researching these techniques has led me to be more convinced than ever that extracting unconventional fossil fuels is not the way of the future – even leaving aside the merits, or otherwise, of using these fuels.
What is fracking?
"Fracking" – short for hydraulic fracturing – is a technique of fracturing rocks with high a pressure fluid. It is mostly used for extracting tightly held hydrocarbons from rock formations.
What are "tightly held hydrocarbons"?
Sometimes oil, natural gas and water occur in underground reservoirs and will flow to the surface if the reservoir is tapped. But often the oil, gas or water is in tiny cracks or fissures in rocks, like shale, or in coal beds. These are called "unconventional reservoirs".
If you drill into these unconventional reservoirs, only a small amount of the fluid, from near the bore hole, will come to the surface. One way of getting more fluid is to make cracks in the rock. The fluid will seep into the cracks and then into the bore hole.
You mentioned water, is fracking used for purposes other than extracting oil and gas?
Yes. It is sometimes used for stimulating groundwater wells. Miners sometimes use it to break away sections of rock. In enhanced (hot rock) geothermal sytems, it is used to heat water for power generation. And it can be used to dispose of dangerous materials, such as radioactive waste, deep underground.
Fracking has not been widely discussed unil recently. Is it new?
No. It was first used by Haliburton in Kansas in 1947, although the modern technique, known as "slickwater fracturing" was developed by Mitchell Energy in the 1990s. The recent upsurge in its use has resulted from the higher price of fossil fuel and the diminishing reserves of conventional oil.
How, exactly, is fracking carried out?
Basically a slurry is pumped into the rock or coal formation, causing cracks to open up. This is done in deep weels – between 1,500 and 6,000 metres underground. Often fracking is carried out at several different depths in a single well.
The slurry is about 99.5% water and silica (builders' sand) with some chemicals.
There are actually two types of fracking, hydraulic fracking and high-volume hydraulic fracking. In (low-volume) fracking between 75,000 and 300,000 litres of water is pumped into the well during its life; in high-volume fracking, up to 11,000,000 litres of fluid is used.
There is much more concern about high-volume fracking. Its possible effects are being studied in many places. Im the meantime, some countries have suspended or banned high-volume fracking.
What chemicals are used – and why?
In a typical fracking well, as much as 400,000 litres of chamicals may be used. These are:
- biocides which kill any microorganisms,
- surfactants which are detergents to stop the oil sticking to the rock,
- viscosity modifiers to make the oil flow more easily and
- emulsifiers which allow the oil to mix with the water being extracted from the well.
A 2011 US House of Representatives investigation found that some 2,500 different chemicals are used. 650 of them were known or suspected carcinogens. 279 of the chemicals were 'trade secrets', so we don't know what they are.
Those that we do know about vary widely in toxicity. Some are chemicals found in common household products like detergents, cosmetics and polishes. Some are highly toxic. These include benzene (which causes cancer and bone marrow failure), lead (which damages the nervous system and causes brain disorders), ethylene glycol (which is antifreeze, a poison), methanol (which causes blindness and death in larger quantities), boric acid (which casuse kidney damage and death) and 2-butoxyethanol (which causes the red blood cells to rupture leading to anemia and jaundice).
Where do all these chemicals end up?
Obviously, the hope is that it all stays put deep underground. Unfortunately, sometimes the fluid seeps back towards the surface; sometimes pipes leak and occasionally a well blows out spewing hydraulic fluid and other byproducts across the ground.
Do the chemicals contaminate the water table?
Until recently, it was thought that fracking was carried out at too great a depth to be of concern. However, the invresing use of high-volume fracking and fracking in conjunction with shallow horizontal drilling, has brought this assumption into question.
In particular, the 2010 film, Gasland, presented claims that chemicals polluted the ground water near well sites in Pennsylvania, Wyoming and Colorado. The oil and gas industry, and particularly a group called Energy in Depth, has called the film's claims into question.
The U.S. Environmental Protection Authority is conducting a major study into that claims that fracking can lead to contamination of drinking or ground water. The final report is not due until 2014 but an interim report is due late in 2012.
Can Fracking Cause Earthquakes?
Only one instance of some small earth tremors, near Blackpool in the U.K., has been found to be probably the result of fracking.
On the other hand, the U.S. Geological Service has reported that several earthquakes in the United States, Canada and Japan have been caused by the injection of fluids into deep wells for waste disposal purposes.
Are there other ways of extracting tightly held oil?
Yes. Sometimes oil occurs mixed with sand and clay at, or near, the surface. This is called oil sand, bituminous sand or 'tar sand' (although it is not actually tar).
If the oil is sufficiently fluid, it can be extracted by progressive pumping. This is used in Venuzuela. The technique is relatively cheap but it only recovers about 5 or 6% of the oil.
Another way of getting the oil is by open-cut or strip mining and then mixing the oil sand with hot water and caustic soda. This causes bitumen to separate out from the sand and clay.The bitumen is then refined to yield the oil. The process uses a lot of water and energy – and it takes about 16 tonnes of sand to produce one tonne (8 barrels) of oil.
This is what is being done in Alberta in Canada:
(Tar Sands Collage. Image by Jumgbim via Wikimedia)
What about natural gas? How is that extracted?
Where gas occurs in coal seams reasonably close to the surface, one technique is simply to drill a lot of wells close together. Often there is water, as well as gas, trapped in the coal seam. Pumping the water out leaves cavities into which the gas flows.
This is being done at Chinchilla in Queensland:
73 of the proposed 18,000 wells near Chinchilla (Image source: ABC)
There are three main problems with this – all of those wells and connecting service roads make the land useless for broadacre farming, what to do with the water and will extracting the water lower the water table.
Is there an alternative to drilling all of those wells?
Another technique is called 'horizontal drilling'. Actually, truly horizontal drilling is practically impossible. What this refers to is drilling at a very shallow angle and making small changes to the angle to try to follow the coal seam. Usually there is a central hub from which up to about ten bores are drilled out like the spokes on a wheel. The "spokes" go for up to about 10 kilometres and then another well is drilled down to intersect end of the horizontal bore.
This is the technique being proposed for accessing the coal seam gas (or "coalbed methane" to use the American term for the same thing) under Sydney.
You mentioned problems with the water that is extracted. What are these?
There is a wide variation in the amount and quality of water extracted in different coal seam gas projects.
In the case of the Chinchilla project, pictured above, initial flows were between 0.1 and 0.8 megalitres a day from each bore. To put that in perspective, the average Australian uses about 1 megalitre of water a year – and the Chinchilla project could have 18,000 bores. On the other hand, the amount of water flowing from a bore declines over the life of the bore, which is about 15 years.
Whatever the exact figure, it's a lot of water! That water will have a amount of salt which differs in different locations. In the case of Chinchilla, each megalitre of water brings up between 5 and 8 tonnes of salt.
As well as all of that salt, coal originates from organic material and always contains contaminants which will be extracted with the water. These include heavy metals, benzene, toluene, ethylbenzene, xylene and radioactive chemicals. So, the salt can't be used for human consumption without very extensive processing. And it can't be allowed to spead over the land because that would destroy the land for agriculture.
Similarly, the water can't be consumed without processing. And even then, there will be a residue of brine to be disposed of.
One solution is to inject the waste water back into ground. However, as mentioned above, the U.S. Geological Service has reported that several earthquakes in the United States, Canada and Japan have been caused by the injection of fluids into deep wells for waste disposal purposes.
Do these techniques of vertical and horizontal drilling involve fracking?
Not necessarily. But fracking can be used in conjunction with them to extract some more gas – typically about another 20%.
Based on sources including:
US Geological Service
Australian National Water Commission
(former) Queensland Department of Environment and Resource Management
ABC Coal Seam Gas by the Numbers
US Public Broadcasting Service: Gasland
Energy in Depth and