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Fracking: frequently asked questions

What about subsidence of the rock once the gas or the CSG is removed?

There is no subsidence as the rock structure beneath the ground is held together by rock-to-rock contact. The gas is only flowing through areas of existing pore space. As an analogy, when water is squeezed out of a sponge, the sponge remains. In any case, as gas is evacuated, it is generally replaced by deeply-buried water. Note that this water is generally saline, and is isolated from the water table, which is much closer to the surface. 

What about the explosions in gas fields in the US, that could happen in NZ

Fracking has nothing to do with explosions.

If explosions do occur, for other reasons, they have to be at the surface where there is oxygen to allow gas to ignite. The industry does everything it can to minimise the risk of an explosion. But like many activities, risk can never be eliminated completely. It is a matter of reducing risk as much as possible and having systems to manage an incident. To date in New Zealand there has never been an explosion in a gas field.

What would happen if water did get contaminated

There has never been water contamination in New Zealand as a result of fracking, or an oil & gas operation generally.

In the case of a NZ fracking operation, such could only occur if the steel casings, and the cement holding them in place, happened to rupture during the fracking operation, at the depth of a groundwater aquifer, and if fracking safety systems failed to shut down. In that event, high pressure in the well would force fracking fluid into the aquifer. It is not impossible for such a chain of events to occur but it is extremely unlikely.

What would happen in a Japan-magnitude earthquake?

Nothing as a result of fracking.

A large tsunami could affect an offshore gas rig, whether or not any fracking was being done. Displacement of a coal seam in an earthquake could cause a natural release of CSG through natural cracks forming in the rock. Recall that most earthquakes occur at depths of more than 5–10km below ground, well below gas or coal reservoir zones and fracking operations.

Even if an earthquake did cause faulting across reservoir zones, the gas would escape anyway, through natural processes. Indeed, this has been a common occurrence over geological time, explaining why exploration wells are often dry – the rock structure looks good for oil or gas, but the hydrocarbons are long gone.

Could fracking cause an earthquake?

It depends what you mean by an earthquake. Earthquakes of the sort that have occurred in Christchurch are caused by the massive forces of nature operating at much greater depths than fracking. It would like comparing a ripple on a pond with a tsunami.

See separate page on earthquakes for more comment on the European Parliament report.