Safe Shale 1; Integrity of the drill way.
I frequently get asked about the safety of shale gas exploration and its effect on land, groundwater and pollution. Well, here is a short discussion on drilling the top hole.
The vertical shaft of a drill down to shale gas is quite likely to be a kilometer, maybe two, or (in old money) a mile or so. Maybe more. That, in itself, is not that much of a new thing. Deep drilling for all sorts of reasons (such as geothermal drilling to bring “free” hot water to heat homes, offices and shops) has been going on, even deeper, for a long time. (And geothermal drilling is often “fracked” and yet nobody complains about that!) What is different about drilling for shale gas is that when the vertical shaft has got to the depth that the geologist thinks is right, the drill turns, in a giant “J” shape, from being vertical to horizontal. In the horizontal bit, the engineers want the hole to leak – inwards to collect the gas!
Common sense tells us that whatever the pollution risks are of leakage from a mile or so down back to the surface, they are very, very small. In practice, it just is not going to happen for one very simple reason. If it was going to happen, it would have done so already during the last few hundred, million years.
That still leaves the worry about the integrity of the vertical shaft. That certainly might travel through strata near the surface which might leak back up to the top, certainly it might drill through aquifers which might be used for human consumption; leakage certainly might cause pollution. How likely is that “might” and can it be controlled?
Leakage of the vertical shaft after construction is known but it is rare. After all, sinking just the vertical shaft is quite likely to cost over £10 million in the UK and, therefore, the investors and engineers are going to be quite careful. The way of covering this risk is to pressure test the vertical shaft before turning to the horizontal drilling. If it leaks, abandon it. In the UK. that is inflicted, independently, by law.
Bill Butterworth, Land Research Ltd, 27 December 16