Pilot Project to Inject Carbon Dioxide Into Basalt for Sequestration

By early August, scientists will have pumped 1,000 tonnes of pure carbon dioxide into porous rock far below the northwestern United States. The goal is to find a permanent home for the carbon dioxide generated by human activities.

Researchers at the US Department of Energy’s Pacific Northwest National Laboratory (PNNL) in Richland, Washington, began the injections into the Columbia River Basalt formation near the town of Wallula on 17 July. The rock contains pores created as many as 16 million years ago, when magma flowed across what is now the Columbia River Basin. Bubbles of CO2 migrated to the edges of the magma as it cooled, forming layers of holes sandwiched between solid rock (see 'Rock steady').

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The Wallula project is the second of two worldwide to target basalt formations, which scientists hope can hold — and permanently mineralize — vast quantities of gas. In basalt, dissolved CO2 should react with calcium and magnesium to form limestone over the course of decades. Until the gas is locked away, the porous basalt layers are capped by solid rock that will prevent leaking. That should eliminate concerns about leakage that have dogged other proposals to store CO2 deep underground, often in sandstone reservoirs.

The basalt reactions are part of a natural weathering process that has helped to regulate atmospheric CO2 levels throughout geological time. Scientists have analysed mineralization in the lab, but it is only now being tested in the field.

Researchers working on the other basalt project, based in Iceland and run by a consortium of US and European scientists along with Reykjavik Energy, made their first CO2 injections last year and will conduct another round this year. Early results look promising, says Juerg Matter, a geochemist at Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York, who is working on the Iceland project. “The mineralization reaction is most likely faster than what we in the community had thought,” says Matter, who has also contributed to the Wallula project. Assuming that holds true for basalt generally, “you reduce the risk of leakage, and you can pretty much walk away from your storage reservoirs”.