Daily Bulletin


The Conversation

  • Written by Henning Prommer, Research scientist, CSIRO

Water produced when coal seam gas (CSG) is extracted from below ground can be safely re-injected hundreds of metres underground, according to new CSIRO research.

Water is pumped out of coal seams to access the gas held within them. CSG in the Surat Basin, Australia, produces on average 70 gigalitres of water each year - a seventh of the water held in Sydney Harbour. What to do with this water is one of a number of concerns voiced by communities around CSG.

Our research shows that injecting large volumes of treated CSG-produced water at suitable locations within the Surat Basin is unlikely to cause any harm to groundwater quality.

However, to achieve this the water has to be treated adequately to eliminate the risk of polluting groundwater with arsenic – a generally immobile toxic element that occurs naturally in some of the rock formations being considered for re-injection.

Why re-inject CSG water anyway?

image Laboratory experiments to determine the release mechanism of arsenic from sediments in the Precipice Sandstone. CSIRO, Author provided

In Queensland, the state government’s policy on managing “produced water”, also commonly known as “CSG water”, is to “encourage the beneficial use of CSG water in a way that protects the environment and maximises its productive use as a valuable resource”.

In many cases the most suitable and socially-accepted option is to treat the water, using reverse osmosis technology, and inject it into deep aquifers. The re-injected water can be used to top-up already stressed aquifers.

However, looking at similar projects around the world, especially from Florida, has shown that injecting clean water underground can sometimes mobilise naturally occurring contaminants such as arsenic.

When rainwater seeps underground and becomes groundwater it changes its composition. During the subsurface passage that can often take thousands of years the groundwater composition changes slowly to successively take on the characteristics of the rocks.

When water with a non-compatible composition is directly injected into deep aquifers, the injected water will also react with the rocks and therefore change its characteristics to one that is compatible with the new host rock. This occurs through the release of elements from the rocks, a process called mineral dissolution.

In addition, arsenic mobilisation can also occur by a process called desorption, in which case loosely-attached ions are released from mineral surfaces. Both processes may proceed until a new balance or “geochemical equilibrium” is established and both have the potential to mobilise toxic elements such as arsenic.

Testing the waters

In our new research, we analysed results from injection experiments at Reedy Creek and at Condabri, both located in the Surat Basin in Queensland, through computer models that can simulate groundwater flow and groundwater quality.

This analysis showed that if and how much arsenic is mobilised depends on the composition of the injected water. From the research we conclude that minimising arsenic release most importantly depends on oxygen being stripped from the water prior to injection of the CSG water.

During the research elevated arsenic levels have been found during a field experiment at one of the sites (Reedy Creek), for which both experiments and computer modelling suggest that arsenic release was triggered by the injected water.

However, computer modelling also demonstrated that this type of arsenic mobilisation could have been completely prevented by adjusting the pH of the injected water to the pH of the naturally-residing groundwater.

The experiments performed at the second research site at Condabri under different experimental conditions showed that arsenic concentrations in the groundwater increased substantially if the injected water was not stripped of oxygen.

When oxygen was not removed from the injected water this caused the dissolution of the naturally-abundant mineral pyrite, or “fool’s gold”. Arsenic is often embedded in trace amounts in this mineral.

What can we do?

The findings from this research were used to guide the design requirements for the large-scale implementation of CSG water injection into the Precipice aquifer. During the treatment process all water is now deoxygenated prior to injection and the pH of the injected water is similar to the natural groundwater.

The Reedy Creek re-injection scheme is now successfully operating and injecting treated CSG water. Since starting the injection in 2015, over 10 gigalitres (GL) has been injected into the Precipice aquifer and the scheme is currently Australia’s largest treated water re-injection scheme.

As a result groundwater levels in parts of the Precipice aquifer have started to rise for the first time in the last few decades.

Authors: Henning Prommer, Research scientist, CSIRO

Read more http://theconversation.com/can-billions-of-litres-of-coal-seam-gas-water-be-safely-reinjected-into-the-ground-67634

Writers Wanted

I regret stopping breastfeeding. How do I start again?

arrow_forward

The missing question from New Zealand's cannabis debate: what about personal freedom and individual rights?

arrow_forward

The Conversation
INTERWEBS DIGITAL AGENCY

Politics

Did BLM Really Change the US Police Work?

The Black Lives Matter (BLM) movement has proven that the power of the state rests in the hands of the people it governs. Following the death of 46-year-old black American George Floyd in a case of ...

a Guest Writer - avatar a Guest Writer

Scott Morrison: the right man at the right time

Australia is not at war with another nation or ideology in August 2020 but the nation is in conflict. There are serious threats from China and there are many challenges flowing from the pandemic tha...

Greg Rogers - avatar Greg Rogers

Prime Minister National Cabinet Statement

The National Cabinet met today to discuss Australia’s COVID-19 response, the Victoria outbreak, easing restrictions, helping Australians prepare to go back to work in a COVID-safe environment an...

Scott Morrison - avatar Scott Morrison

Business News

What happens to all those pallets?

Pallets — they're not something everyday people often give much thought to. But they're an integral part of any business which receives or distributes large quantities of goods. But once the goo...

News Company - avatar News Company

Ten tips for landing a freelance transcription job

Transcription jobs are known to be popular in the field of freelancing. They offer fantastic job opportunities to a lot of people, but there are some scammers who wait to cheat the freelancers. ...

News Company - avatar News Company

How To Remove Rubbish More Effectively

It can be a big task to remove household rubbish. The hardest part is finding the best way to get rid of your junk. It can be very overwhelming to know exactly where to start with so many option...

News Company - avatar News Company



News Company Media Core

Content & Technology Connecting Global Audiences

More Information - Less Opinion