Something in the water

So, water. Useful stuff. We can perhaps conclude that faulty mining well casing is a source of methane in drinking water, but what about that somewhat mysterious “fracking fluid”? The evidence for this one is not so clear cut.

Image: ProgressOhio

I should probably explain why I keep on calling them mysterious, even though we largely know what sort of additives they are likely to contain. In the United States, disclosure of the ingredients in fracking fluids by drilling companies is largely voluntary, and many additives are not disclosed due to commercial sensitivity. The industry backed website FracFocus allows for the submission of additives by drilling companies, but regulation does not mandate their disclosure and it is up to the companies to decide what and whether to submit. It should be noted though that in the UK, regulations oblige mining companies to disclose all additives.

Hydraulic fracturing tends to be performed at great depth, an average of around 2500m below ground in the US, and the pressurisation of the fluid takes place in small “sections” of the horizontal well. This allows for greater control of the pressure, which can be optimised for the surrounding geology. Consequently, the chances of fracking fluid finding their way into local groundwater sources is fairly low, as it would have to migrate through hundreds of meters of rock. However, the depth at which fracking takes place is a function of the geology, rather than a measure to protect groundwater, and may range from over 5000m to as little as 30m. While fracking is not frequently performed at such shallow depths, this is well within the range of groundwater.

Even with a close vertical proximity to groundwater, our primary concern is whether any fracking fluid is allowed to migrate far enough from the mining well to pose a contamination hazard. It’s in the interest of mining companies to closely monitor the extent of the fractures which they induce, as too extensive a fracture could result in the escape of the gas, and too small would mean that they won’t make the best possible return on their investment.

Broadly speaking, most investigations have failed to find evidence of the chemicals associated with fracking fluid in drinking water. However, under some geological conditions, there is some evidence (pdf) of migration from fracture sites into groundwater reserves.

The vast quantity of water used during a hydraulic fracturing operation has to be disposed of after use. Often it is sealed underground in an “injection well”, and left there. This is associated with another issue, as the less constrained injection of pressurised water has the potential to unleash seismic energy stored in the surrounding geology. There is evidence that this has happened(pdf) (we’ll look at this more thoroughly in a future post).

So what can we take away from this? Fracking fluid may indeed find its way into groundwater supplies, but only under specific geological circumstances. It would seem that the biggest issue is with injection wells, where companies dispose of used water, rather than the actual mining site, since they’ll generally be under higher pressure and for a longer duration. Also, earthquakes.

Next time:

• A little bit about the stuff they add to fracking fluids. I’ve been promising it for ages but I keep running out of words.
• How much water? That’s a lot of water.
• Earthquakes? I’d rather the ground didn’t move, thank you.