With so much talk around onshore oil and gas drilling it can be difficult to get your head around what’s what — such as telling the difference between conventional, CSG (coal seam gas), and shale gas drilling.
While outrage over onshore oil and gas drilling in Australia hasn’t quite reached the frenzied heights it did during the commissioning of a trio of LNG plants in Queensland, it still remains a controversial issue.
For example, only recently Labor has backed plans to open up the Beetaloo Basin in the Northern Territory for onshore gas development.
While proponents point to the massive domestic resource which could be developed, those opposed to the drilling are worried about the effects of releasing more carbon into the atmosphere and the potential effects on groundwater.
General alarm and panic over coal seam gas and shale gas drilling has left developers of conventional onshore gas resources frustrated — as the latter doesn’t carry the same sort of risks as the former forms of drilling (although it does still carry risks).
Meanwhile, CSG doesn’t require fracking in the majority of cases, meaning that the risks associated with that aren’t present.
Shale gas drillers can be frustrated meanwhile because it doesn’t involve de-watering.
What the debate over onshore gas development has in effect done is lump in all types of drilling into the one thing — so the average punter has very little sense of the unique opportunities and risks each carries.
So, we’ve attempted to break them down here:
What is Coal Seam Gas drilling?
Coal Seam Gas only came to Australia in early 2010 as drilling for LNG plants in Queensland started to ramp up — so there was a lot of confusion initially about what it actually was.
Referred to as ‘Coal Bed Methane’ in other countries, it involves drilling into sedimentary layers below the water table and perforating the formation — with these formations roughly 300-500m below the ground.
These layers are referred to as coal seams, and as you can probably guess, are made of coal and contain big volumes of methane.
However, they also contain huge volumes of water — which can’t really be used for agricultural purposes.
So to get the gas out of the coal seam:
The driller will need to drill down and perforate the formation
Once the perforation has been done, it will suck out or ‘flowback’ the water in the formation
Once the water is out, the gas will follow
With CSG drilling, only a minority of wells are completed using hydraulic fracturing (or fracking), mitigating the risks of fracking fluids finding their way to the water table.
Here’s a quick, simplified explainer from Arrow Energy:
On an individual well level, CSG carries less risk than a shale gas well despite being closer to the aquifers where drinking and irrigation water is drawn from.
However, there are concerns about what happens when you remove water from 40,000 wells and what that does to geology in the area as a whole — as is happening in Queensland.
What is Shale Gas drilling?
Shale gas is mined much, much deeper than CSG and therefore is more expensive — but also almost always requires fracking.
While CSG can be found about 300-500m under the surface, shale intervals are found kilometres underground.
The first step of the process when producing CSG or shale gas is pretty much the same — drill down and perforate the target formation.
However, shale gas wells are often drilled down vertically, and then go off horizontally within the target formation to give the driller access to as much of the formation as possible.
After all, if you’re spending all that time and energy going deep you want to get as much out of the ground as possible.
The target formation is then perforated, as it is during CSG drilling — but this is where it starts to get different.
Because of the geology of shale, perforations made won’t stay open on their own — so drillers will inject ‘proppant’, which is a mixture of water, chemicals, and sand into the fractures made by the perforations to extend them and to keep them open.
With the perforations now made, the gas can flow to the surface along with the proppant.
Here’s a quick explainer video from the CSIRO:
Concerns around shale gas come from the risk of the chemicals from the proppant leaking into other layers of geology from the cracks made during perforation — and from poorly-designed production casing.
Meanwhile, each well can use a huge amount of water in the proppant — leading to questions around where that water comes from and how it will be returned to the environment afterward (if at all).
What is Conventional Gas Drilling?
You don’t see as much conventional drilling around as was once the case, but it still occurs.
Put simply, conventional drilling starts out the same way as shale or CSG drilling, but doesn’t really require anything else for gas to flow to the surface.
A conventional well simply involves drilling down, perforating, and letting the gas flow.
Because it doesn’t involve de-watering or hydraulic fracturing, it’s thought to be safer than CSG or shale — but CSG and shale drilling exist in part because all the sweet conventional drilling spots have been drilled.
Take Texas for example.
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It was traditionally home to conventional oil drilling (think the beginning of Beverly Hillbillies) — which made the state what it was.
However, by the early 2000s the sweet spots were all taken.
Oil and gas drillers knew there was a great resource of shale available, but the technology just wasn’t there to extract it economically.
However, a higher oil price supported the development of technology (most notable horizontal drilling), and the ‘shale gale’ of the mid 2000s occurred.
Because it doesn’t involve de-watering or hydraulic fracturing, there’s less likely to be environmental issues associated with drilling — beyond drilling for more fossil fuels.
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