Give me a crash course in . . . fracking

What is fracking?Fracking is short for hydraulic fracturing – using water to fracture rocks to drill for natural gas.

How was it invented?Engineers have struggled to liberate fossil fuel from tiny fissures in shale rock and tight sandstones. In conventional gas drilling, the gas is in reservoirs that can be tapped by simply drilling a vertical well. In 1981 an engineer named George Mitchell found that you could mix horizontal drilling with hydraulic fracturing to unlock vast quantities of gas.

Why do we need to know about it?Two companies have targeted areas in Leitrim, Cavan and Fermanagh that they believe contain potentially tens of billions of euro worth of gas. At a public meeting about the process in Carrick-on-Shannon during the week, executives of Tamboran, which wants to drill in north Leitrim, were heckled by protestors. The Government has promised an environmental impact assessment before any fracking takes place, but this doesn't seem to have reassured many who attended the meeting.

How does it work?First you drill a vertical wellbore, then a horizontal one using motors that allow for directional drilling along a seam of shale. You run a steel pipe into the wellbore, which can be up to 4,000m deep, and pump cement around the outside of it to lock it into place. Then you use perforating guns with explosive charges placed at intervals along the pipe to blast small holes in both the pipe and the concrete. Next you pump the fracking fluid, consisting of water, sand and chemicals, through the holes at a pressure of 5,000 pounds per square inch. This shatters the shale and releases the gas, which flows up the pipe to the surface.

So what is the end result for the gas industry?The process has opened up hundreds of thousands of square kilometres of territory around the world to gas drilling. Time magazine called shale the "rock that will power the world". In the space of a decade the US has gone from being the biggest importer of natural gas to the biggest producer in the world. Poland, Germany, China and even Ireland have vast shale deposits that could be exploited.

An abundant form of energy – what could possibly go wrong?All energy comes at a price. In the case of fracking, the price has been environmental damage, as shown by the documentary film Gasland. The process allows water contaminated by the fracking fluid to flow back up the pipe and into aquifers. It also allows natural gas to seep into the water supply. In one striking scene in the film, householders in Colorado are seen lighting their water because methane had escaped into it. A panel of experts, set up by US president Barack Obama, concluded last month that fracking had "enormous potential" but also serious environmental impacts, and called for tighter regulation.