A new tool to ensure the safety of injecting CO2 underground

A new tool to ensure the safety of injecting CO2 underground
Aerial view of the study site at In Salah. Credit: Google Earth/CNES Astrium

Sequestering carbon dioxide underground is likely to play a key role in meeting reduction targets set at the IPCC conference in Paris last year. Researchers at EPFL have developed a simulation tool to evaluate the impact of the injection process on the host rock.

Over the course of four and a half years, the ground surrounding the In Salah -fired power plant in the Algerian desert rose by sixteen millimeters. This rise was triggered by the injection of the carbon dioxide emissions captured at the plant into a deep aquifer, 1800 meters underground. The heaving of the bedrock at In Salah was benign, but injecting excessive amounts of gas into the subsurface could potentially fracture the impermeable layers keeping the gas in place. Researchers at EPFL have developed a computer model that simulates the geological impact of injecting CO2 underground and assess how much gas a reservoir can safely accommodate. They published their results in the International Journal of Greenhouse Gas Control.

Underground CO2 sequestration is already being used at several sites around the world to keep the greenjouse gas out of the atmosphere. The Paris agreement, which seeks to limit the extent of anthropogenic climate change, will likely accelerate the adoption of this technology, which according to a study published in 2010 could be feasible in parts of Switzerland as well. The complex and highly variable geology of potential sequestration sites around the world call for the development of tools to determine under what conditions their impermeability can be assured.

The injection phase is most critical, says Li Chao, a researcher at EPFL's Chair "Gaz Naturel"-Petrosvibri and co-author of the study with Prof. Lyesse Laloui. "When CO2 is injected into a deep aquifer, sometimes thousands of meters underground, it is much cooler than the surrounding rock and compressed to the point that it occupies 500 times less volume than it would in the atmosphere. Because of its temperature, its pressure, and the volume it occupies, it interacts with the surrounding rock " he explains. This can deform the rock, causing geological instabilities, and in the worst case, fracture the cap-rock that seals the aquifer, allowing the gas to escape to the surface.

Chao says he can use his simulation to determine the pressure up to which CO2 can safely be injected in a given geological setting. To test it, he and his co-author attempted to replicate the observed heaving in In Salah, caused by four and a half years of CO2 sequestration. While the cold gas contracts the host rock surrounding the injection site, its high pressure increases the size of the pores in the rocks. By coupling thermal, hydraulic, and geomechanical processes in one simulation, Chao and Laloui were able to determine how these competing forces conspire to shape the reservoir and the rock layers above and around it.

"Our simulation results came very close to matching the satellite observations," says Chao. In the future, he hopes to further develop his model, which can be applied to other types of CO2 sequestration sites, from abandoned oil or gas fields, to saline aquifers, to simulate for the formation of fractures in the bedrock.


Explore further

Ancient rocks yield hard facts on safe storage of greenhouse gas

More information: Chao Li et al. Coupled multiphase thermo-hydro-mechanical analysis of supercritical CO2 injection: Benchmark for the In Salah surface uplift problem, International Journal of Greenhouse Gas Control (2016). DOI: 10.1016/j.ijggc.2016.05.025
Citation: A new tool to ensure the safety of injecting CO2 underground (2016, July 1) retrieved 27 May 2019 from https://phys.org/news/2016-07-tool-safety-co2-underground.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
23 shares

Feedback to editors

User comments

Jul 02, 2016
Fracking is a fossil fuel industry and adding emissions roughly equal to processing oil full carbon-footprint and leakage is not well represented .

Sequester of CO2 won't stop anything, it won't cool the planet, we put up 10-petagrams of carbon last year to get rid of for just that year, get it that the amount of carbon being added by fracking will never be removed for thousands of years by sequester?

Or, are you one of that people that thinks we haven't entered a geologic excursion yet?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more