Carbon capture lowers emissions.

Depleted hydrocarbon reservoirs have a smaller (10%) storage potential compared to deep saline aquifers but are seen as a critical early opportunity in developing geological CO2 storage technologies. Fortuitously, CO2 has historically been injected into numerous depleted hydrocarbon reservoirs as a means of enhanced oil recovery (CO2-EOR). This provides a unique chance to evaluate the (bio)geochemical behaviour of injected carbon over engineering timescales.

‘CCS will be a key tool in our battle to avert climate change. Understanding how CCS works in practice, in addition to computer modelling and lab-based experiments, is essential to provide confidence in safe and secure CO2 geological sequestration,’ said Dr. Rebecca Tyne, Dept Earth Science, the University of Oxford

In a paper published, today in Nature, Dr. Rebecca Tyne and Prof. Chris Ballentine from Oxford University, lead a team of international collaborators to investigate the behaviour of CO2 within a CO2-EOR flooded oil field in Louisiana, USA. They compared (bio)geochemical composition of the CO2-EOR flooded field with that of an adjacent field, which was never subjected to CO2-EOR. Data suggest that up to 74% of CO2 left behind by CO2-EOR was dissolved in the groundwater. Unexpectedly, it also revealed, that microbial methanogenesis converted as much as 13-19% of the injected CO2 to methane, which is a stronger greenhouse gas than CO2.

Methane is less soluble, less compressible and less reactive than CO2, so, if produced, it reduces the amount of CO2 we can safely inject into these sites. However, now this process has been identified, we can take it into account in future CCS site selection,' said Prof. Chris Ballentine, Dept. Earth Sciences, the University of Oxford