Fracking has been part and parcel of the oil and gas industry for many years and has been brought into sharp and controversial focus by the fast-growing shale gas (and oil) extraction industry in the US.
There is growing sensitivity to the practice in Europe, even though there is zero commercial production of shale gas and very few exploratory wells drilled so far.
Indeed, fracking for shale gas is currently banned in a number of EU member states, including France and yet the French government has just given approval for hydraulic fracturing of geothermal wells.
French geothermal energy plans are ambitious with three licences issued and 18 more apparently pending.
The concept of geothermal fracking has yet to penetrate the UK where Cuadrilla caused a major upset when use of the technique in its hunt for shale gas near Blackpool caused localised mini-quakes in April 2011.
Meanwhile, in the US, the method is now being actively promoted and geothermal company Ormat recently connected the first enhanced geothermal well to the electricity grid, adding a further 1.7MW (megawatts) capacity to the Desert Peak project in Nevada State.
This is one of a number of enhanced geothermal projects partially funded by the US Department of Energy.
By fracking at Desert Peak, Ormat was able to hike energy production by 38%.
Conventional geothermal wells tap underground reservoirs of hot water and convert the heat into steam, which drives electricity-producing turbine. With enhanced geothermal, fluids are pumped underground to fracture underground rock and stimulate the flow of liquids across hot rocks.
The energy source – underground heat – is renewable and clean, but unlike wind and solar, geothermal wells can operate around the clock and provide baseload power.
A 2006 MIT study identified that the geothermal potential in the US is vast. But until the small Desert Peak project, enhanced geothermal systems were the realm of research and dreaming.
Ormat believes that fracking would transform many thousands of dud geothermal wells drilled across the US over many years. The term game-changer has been used.
The practice is commonly used by the conventional oil and gas industry to get test and production wells to flow commercially.
In the US, drilling a brand-new geothermal well costs $4-7million, whereas re-entering and fracking would be low-cost according to the company.
In this project, Ormat pumped water from its existing hot-water source at a pressure between 800 and 1,000 pounds per square inch to create fractures in the rock. That allowed water to flow through a web of cracks at a much higher rate, going from 15 litres to more than 6,000 litres per minute, a change that made it commercially viable.
Part of the project was to implement a protocol for monitoring and communicating the effects of fracturing rock with high-pressure liquids. Concern over tremors caused by enhanced geothermal has derailed other projects.
In this case, “micro seismic events” were described as minor and, as the well was drilled in an arid region, there was no local population to disturb.
The publishing of more detailed data on the project is thought to be imminent.
It will only be a matter of time before questions are asked regarding the impact of geothermal hydro-fracking, which involves both injection of water under very high pressure and acidisation of target rock formations.
The issues could turn out to be the same as for the extraction of gas and oil from shales, including the risk of aquifer contamination.
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