Fracking and Carbon Sequestration: a Beautiful Future Together???

Anthropogenic combustion of fossil fuels has led to an excess of atmospheric carbon dioxide... in order to counteract this, and maintain the delicate equilibrium, the technique of Carbon Capture Sequestration - or CCS - has been developed. CO2 is captured at power plants and  transported as a supercritical fluid through pipelines to offshore/onshore geo-sequestration sites. These are commonly depleted oil and gas fields or saline aquifers, acting as a porous reservoir rock; the site is then capped by an impermeable cap-rock that prevents the migration of the CO2... and Bob's your Uncle- 1000's tonnes of carbon dioxide removed from the atmosphere and stored underground.

Image showing the geological storage options for CO2; number 5 applies to us frackers.

Image URL: http://www1.gly.bris.ac.uk/BCOG/images/CCScartoon.jpg


For more information visit the CCSA site: http://www.ccsassociation.org/

The even better news is the techniques of hydraulic fracturing and carbon capture sequestration could be combined in future exploits. This works through fracturing of the shale by pumping supercritcal CO2 into the shale formation, instead of using the standard fracking fluid- a water, propant and chemical additive mixture. Furthermore, the shale has a higher affinity for carbon dioxide than it does for methane; this means that the shale will preferentially take up CO2 and release CH4. This seems like a win-win situation: more methane can be extracted and a greenhouse gas is stored in its place.

New research published by Tsuyoshi Ishida (http://geo.kumst.kyoto-u.ac.jp/lab/member/Ishida_t/English.htm)  from the Department of Civil and Earth Resources Engineering, Kyoto University, entitled 'Acoustic Emission Monitoring of Hydraulic Fracturing Laboratory Experimentwith Supercritical and Liquid CO2,' further highlights the advantages of combining the techniques. Ishida's team found that using carbon dioxide in its supercritical form leads to the production of a 3-dimensional fracture network that greatly increases shale-gas extraction (this is opposed to a typical 2-dimensional fracture network seen in shale fractured with water. It is though this difference is caused by the low viscosity of supercritical CO2, which has 1/10 the viscosity of water. The report is unfortunately unavailable online, but can be viewed through the Wiley Library at (http://onlinelibrary.wiley.com/doi/10.1029/2012GL052788/abstract;jsessionid=FC83C33F80EA526FEC11FE0553B6A4D2.f01t03)

A report conducted by the US Department of Energy, in 2006, entitled 'Geologic Storage Options and Capacities for Carbon Dioxide Sequestration in the Midwest Regional Carbon Sequestration Partnership' is available at the following link: (http://www.netl.doe.gov/publications/proceedings/06/carbon-seq/Tech%20Session%20147.pdf). In this report, shale formations which have been hydraulically fractured were found to be the second most effective way of storing CO2.; fractured shale beds were designated to be able to hold 45 gigatonnes. In first place were the saline aquifers with a slightly embarrassingly high 470 gigatonnes.

However, when it comes to fracking, nothing is ever that plain cut! In a new research paper by T.R Elliot and M.A Celia,of Princeton University entitled 'Potential Restrictions for CO2 Sequestration Sites Due to Shale and Tight Gas Production' (http://pubs.acs.org/doi/abs/10.1021/es2040015), it is revealed that fracking may actually have detrimental effects for the geo-sequestration of carbon dioxide. This report concluded that there is commonly a large overlap between sites used for fracking and optimal CCS sites. This is because, under normal circumstances, a shale bed overlying a porous reservoir rock will act an impermeable cap rock, preventing migration of a carbon dioxide plume. However, if the cap- rock has been fractured,it could provide pathways for CO2 to leak back into the atmosphere. The studies shocking conclusion was that up to 80% of the potential on-shore CCS sites in the USA could become redundant due to hydraulic fracturing operations.

If the technologies surrounding CCS can be refined to restrict the migration of carbon dioxide through fractured shale beds, this may have massive implications for fracking all over the globe. Not only will the yield of shale-gas increase but there could be a net storage of CO2. Furthermore, if carbon dioxide were to be used in place of water, this may alleviate the issues associated with the exploitation of local water resources and it would remove the need for the use of harmful chemical additives from frackwater. To me, this seems like the perfect PR for the government to use in a bid to increase public support for fracking.... so watch this space and get ready to hear a lot about CCS!!