14 DAY TRIAL // An international team of experts including scientists from the US Department of Energy's (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) is currently testing to see whether depleted natural gas reservoirs can be used as carbon sequestration facilities in the long run.
Their proof-of-concept experiment is being conducted in southeastern Australia, and is meant to see whether geological carbon sequestration is feasible at such locations. Carbon capture and storage (CCS) technologies began receiving a lot of attention in recent years.
CCS technologies should be installed on the smokestacks of fossil-fuel powered electricity plants, so that excess carbon can be removed from the fumes, and then somehow injected underground. If this new idea works, then the chemical could be placed inside the depleted reservoirs.
Such re-purposing would enable the permanent storage of carbon at such locations, not just the temporary type. Given the sheer number of gas reservoirs, this approach would tuck away sufficient amounts of carbon to make a notable dent in global carbon dioxide emissions.
The issue with carbon storage is that the space containing it needs to seal it from the outside world completely. This is why the team working in Australia installed numerous measuring outposts around the boundaries of the former gas reservoirs, as well as in the ground.
The idea was to measure potential carbon leakages in the groundwater and soils, as well as in the air. During the actual tests, which began in April 2008, and lasted for 18 months, more than 65,000 tons of CO2-rich gas was injected in the ground.
This is the equivalent of about 130 tons of CO2 per day, investigators say. In practical terms, this means that the entire carbon output of a small-scale, 10-megawatt power plant could be rendered harmless to the environment.
Ten megawatts of electricity are enough to supply about 6,000 average households in the United States with electricity for a day. During the experiments, the team found that there were no avenues for the gas to escape. No discernible CO2 concentrations were found in the air, soil or groundwater.
“The CO2 stayed within the reservoir and behaved as expected,” explains mechanical engineer Barry Freifeld, who is based at the Berkeley Lab Earth Sciences Division. He was part of the team that set up the monitoring equipment around the reservoir, and then interpreted their readings.
“We found what we expected. The CO2 largely replaced the volume previously occupied by the natural gas. The reservoir had filled with water since the natural gas was extracted, and we watched as the injected CO2 pushed the water to a level below our instruments,” he concludes.