It is the uncomfortable truth that 'spent' fracking fluid is left to reside in the shale formation into which it was injected after drilling for natural gas has ceased (http://www.dangersoffracking.com/). This fracking fluid is composed of water (50 million gallons per well), propellant (usually sand) and a whole host of chemical additives, listed here: (http://fracfocus.org/chemical-use/what-chemicals-are-used).
There have been many concerns in recent years about the likelihood of aquifer contamination due to the migration of spent fluid, away from the site of injection. Previous suggestions regarding the potential for aquifer contamination have been dismissed by fracking companies; this is largely because fracking operates at depths of around 2000m deeper than those of shallow aquifers exploited for drinking water. Indeed, a new preliminary report published by The National Technology Laboratory, Pittsburgh, suggests that fracking fluids remained in-situ at the Pittsburgh site in Greene County, Western Pennsylvania. The study, backed by the Department Of Energy (DOE), placed radioactive markers in the fracking fluid to monitor its progress...or lack of progress as the case proved to be. The report is currently unavailable as it the study is still ongoing, but a nice summary of these preliminary findings is found in the Huffington Post (http://www.huffingtonpost.com/2013/07/19/pennsylvania-fracking-study_n_3622512.html).
Although this appears to be a victory for the fracking companies, and probably a welcome relief for the residents of Greene County, it is important to remember that finding one well without contamination is far from providing any conclusive results about other wells. Furthermore, the report is still ongoing and has yet to be subject to independent peer review.
On the other side of the coin, a recent study conducted by Tom Myers, published in the peer-reviewed journal Ground Water (http://onlinelibrary.wiley.com/doi/10.1111/gwat.2012.50.issue-3/issuetoc) suggests that hydraulic fracturing may have serious implications for groundwater sustainability. Myers used a multi-component modelling system in an attempt to model the migration pathway of such fracking fluids. The results appear to show that fracking fluids could reach shallow drinking aquifers in as little as three years. This may be through zones of secondary permeability, including joins; the reactivation of local faults or 'leak' in the cap rock over the shale.
Myers, who has worked for both the government and conservation group had this to say:
“If contaminants reach natural fractures under pressure, the upward flow has the potential to be enhanced greatly. It can flow upward if there’s a pathway and unless it’s completely impermeable, there’s always a pathway. It’s just a question of how long it takes.”
However, researchers questioning the validity of this report are the first to point out that it was actually commissioned by a New-York based environmental group (http://www.catskillmountainkeeper.org/) that oppose fracking. Could there be some research bias? The plot thickens as Professor Terry Engelder, from the geoscience department of Pennsylvania State University, has discredited the results. Engelder has laid claim that the computer model used to generate results contains inherent errors that scewed the results.
I believe the contradictory reports regarding spent fracking fluid migration, further reinforce the necessity for site-dependant monitoring of fracking wells. This means taking into consideration the unique factors of the regional geology such as the occurrence of local fracture networks or the location and nature of faults in the area. It also highlights the importance for tighter regulations and controls of drilling sites, including bore hole monitoring.There is also a requirement for an evolving manual of 'best practice' that can keep all fracking sites abreast of developments in fracking safety and hazard mitigation.
Other than the concern that fracking fluids will migrate up due to pressure, is it possible that an excess amount of fracking fluids injected into the formation may cause instability? Or is it impossible because the target formation is way too deep?
ReplyDeleteInjecting the huge volumes of water required for fracking at such high pressures can cause instability in shale formations and lead to micro-seismic events. There have been numerous incidences of this, e.g Caudrilla Resources fracking well at Blackpool 2011. Check out this link for more info- its an article on a new paper that says the injection of fluid can trigger swarms of earthquakes at other sites miles away! http://www.reuters.com/article/2013/07/11/us-science-fracking-earthquakes-idUSBRE96A0TZ20130711
ReplyDelete