What do the industry’s words and phrases really mean?
‘Conventional’ gas or oil is held between layers of rock and can be extracted quite easily by drilling a normal well.
‘Unconventional’ gas or oil is trapped tight in small holes and cracks inside certain rocks, so it can’t be extracted by ordinary drilling. To get at the gas or oil the drilling companies have to shatter the rock.
Shale is a sedimentary rock which contains this ‘unconventional’ gas (methane). In Fermanagh the shale layer is quite close to the surface, at around 500 – 1200 metres underground. In other countries, shale containing gas tends to be much deeper, e.g. in the USA it is usually between 2500 and 4000 metres below the surface.
Traditional fracking is a technique used since the 1940s to flush out conventional gas and oil, typically using around 80,000 gallons of water per ‘frack’. It was used in Fermanagh in the 1980s and in 2001 on a few test wells.
High volume hydraulic fracturing (HVHF) is a new technique for extracting
‘unconventional’ oil and gas. It was first used in the early 2000s but has only been commonly used in the USA since 2005. Unlike traditional fracking, it uses immense quantities of water (around a million gallons per ‘frack’) and very high pressure. This is the technique proposed for extracting shale gas in Fermanagh.
Slickwater or fracking fluid is the mixture of water, sand and chemicals pumped at high pressure down well bores (pipes) to shatter the rock beneath. Some of the methane inside the rock will escape into these pipes and up to the surface.
Horizontal drilling is used with HVHF to allow operators to frack large underground areas.
Multi-well pads allow the operators to drill several wells on a single site, with horizontal bores extending in all directions. The plan for Fermanagh is to have at least sixty of these sites, each with twenty-four wells.
Flowback fluid is the liquid left after the fracking process – a mixture of fracking fluid, high concentrations of salt and other substances such as heavy metals and benzene. Some of this will stay underground and some will return to the surface.
If more information on Fracking, click here.