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MEASURING the effectiveness of CCS in underground reservoirs can now be undertaken via the well used to inject the gas, eliminating the need to drill separate measurement wells.

This could provide savings of upwards of US$5m. Injected CO₂ can be trapped in the pores of sandstone reservoirs, dissolved in the saline formation water present in the sandstone, or remain free. Led by Australia’s Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC), a team including US, Korean, Canadian and New Zealand researchers has developed a methodology to establish the proportion of injected gas trapped permanently in the sandstone.

The work at the Otway Project in Victoria involved drilling a 1500 m well and conducting a series of injections, extractions and sampling over several months.

“The team has successfully pulled off a remarkable series of sub-surface investigations that are right at the cutting edge of storage science research,” said Richard Aldous, CEO of CO2CRC.

One stage of the testing involves injection of krypton, which is inclined to bond with water molecules, and xenon, which is inclined to bond with CO₂. Measurements of the amounts of both gases that can subsequently be drawn out of the reservoir provide a guide to the amount of CO₂ that has been trapped.

“If we back-produce the tracers and compare the concentrations to what was injected we can determine how much of the xenon has bonded with the CO₂ which remains in the formation,” said Matthias Raab, the CO2CRC’s Program Manager Geological Carbon Storage.

Other tracers with different propensities to react with CO₂ are also injected.

“We injected three different reactive ester tracers -tripropionin, triacetin, and glycol diacetate – that slowly hydrolysed in the reservoir and then partitioned between the mobile water phase and the immobile supercritical CO₂ phase, forming products with differing partition coefficients.” Raab said. ”Applying a reaction model will then explain the separation of compounds and can be used for the calculation of residual gas saturation.”

The CO2CRC will publish the research findings to make the technology available to other CCS projects.