Ocean aquifers could be drilled by oil rigs retooled for water

A new study has found large quantities of fresh water, trapped below the clay of the seabed - and repurposed oil rigs could be used to get it out.

What to do with oil rigs in a post-oil economy? These large, bulky vessels could have other uses that aren’t quite as environmentally-damaging - like, for instance, extracting fresh water from giant undersea aquifers.

A new study in Nature has found that continental shelves around the world are holding an estimated half a million cubic kilometres of either fresh or low-salinity water. This is good news for many of the world’s largest cities, in places like China, Australia, the Americas and southern Africa where growing populations need more and more fresh water.

Here’s Vincent Post from the US National Centre for Groundwater Research:

The volume of this water resource is a hundred times greater than the amount we've extracted from the Earth's sub-surface in the past century since 1900. Knowing about these reserves is great news because this volume of water could sustain some regions for decades.

So when it rained, the water would infiltrate into the ground and fill up the water table in areas that are nowadays under the sea. It happened all around the world, and when the sea level rose when ice caps started melting some 20,000 years ago, these areas were covered by the ocean. Many aquifers were - and are still - protected from seawater by layers of clay and sediment that sit on top of them.

There are two ways to access this water -- build a platform out at sea and drill into the seabed, or drill from the mainland or islands close to the aquifers.

Oil rigs could be repurposed for this kind of drilling, it’s suggested. They often already drill into aquifers while exploring for oil or gas, ruining the water quality, or even use them as a place dispose of drilling waste like carbon dioxide.

Aquifers, however, are a non-renewable resource, and like most non-renewable things we humans are proving adept at using them up. According to a study from last year, also published in Nature, the footprint of global groundwater use is 3.5 times higher than the rate at which it’s replenished, endangering as many as 1.7 billion people who rely directly upon the most under threat sources.

More water would seem to be intuitively a good thing, but that shouldn’t distract from the need to improve our ability to conserve the water we use - otherwise, much like fracking of natural gas, it’s merely delaying an inevitable disaster. And, while the irony of turning a tool of climate change like an oil rig into something that mitigates it might seem cute, let’s not forget that the infrastructure required to power and transport that water from the rig might well be just as polluting as what it replaces. Aquifer depletion rates have been increasing, in part, because of climate change-driven factors like desertification.

So, in related news, it’s nice to see another piece of oil rig repurposing announced this week - Australian firm AquaGen Technologies wants to deploy its tidal power generators on them. A series of floating buoys move up and down, generating power that can be used to power other equipment, or be transferred back to land, or even be used to desalinate water.

Look, here’s a video:

It’s not much, of course, but it’s a nice start, and another example of what we might come to use dead fossil fuel infrastructure for in the future.

An oil rig in the Gulf of Mexico, August 2013. (Photo: Getty)

Ian Steadman is a staff science and technology writer at the New Statesman. He is on Twitter as @iansteadman.