As we exhaust more easily accessible natural gas reserves, countries across the globe are increasingly turning to shale gas. But how do you release gas that’s imprisoned in millions of tiny pores inside shale rock, deep beneath Earth’s surface? The answer is hydraulic fracturing, or fracking. Fracking involves drilling deep into rock and pumping a highly pressured jet of water, sand and chemicals down the wellbore. This forces a network of tiny cracks to open up and spread through the impermeable rock, allowing pockets of gas within the rock to seep out. The main ingredient that makes up fracking fluid is water. Since water is incompressible, it can pass on the extreme pressures needed from the pump to the shale rock over 2,000 metres (6,560 feet) below. Sand or ceramic beads act as ‘proppants’, holding the cracks open after the pressure drops and while the gas is collected. Finally, a cocktail of different chemicals is added. Their uses range from averting micro-organism growth to preventing corrosion of metal pipes, maintaining fluid viscosity and reducing friction during extraction. Hydraulic fracturing was first used in the 1940s, but is far more efficient today. The advent of horizontal drilling in the Nineties, for instance, made wells far more productive, making the operation economically viable. While fracking has allowed governments to unlock previously unreachable and abundant shale gas resources, it has sparked concerns among some geologists and conservationists. A fracking well uses millions of litres of water per frack, putting pressure on local water resources. Around half of the fracking fluid remains in the rock and, although much deeper than groundwater, some fear it could, over time, contaminate drinking supplies. The fluid recovered at the surface also needs to be disposed of safely. Finally, geologists must ensure fracking sites are far away from fault lines since they can increase the likelihood of earthquakes and tremors in at-risk areas.
