- Potential pollution from the top hole.
- Integrity of the drill way.
- Safe, environmentally friendly, drilling fluids
By Bill Butterworth
4 December 2014
The most common objection to shale gas exploration is pollution risk. That comes down to a simple analysis; the risk depends on what gets put down the hole, what is drilled through and how what comes out of the hole is managed. Add to that whether the vertical drill-way, or “top hole” can be safe.
The vertical shaft of a drill exploring for shale gas is quite likely to be a kilometre, 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 for a long time. 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 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. This shaft is like a telescope of concrete with steel pipes inside. Each stage of the telescope can be pressure tested before progressing further to build the next, lower, stage. This vertical shaft certainly might travel through strata near the surface which might leak back up to the top. It certainly might be drilled 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.
That, however, still leaves the drilling and construction of the vertical shaft. It might well go through an aquifer. How is this risk covered? Well, in the USA it may not always have been considered. There has, undoubtedly, been pollution from unscrupulous operators there. Regulation and inspection could, in theory, identify, control and eliminate this risk. That leaves the question of exactly how to control the risk itself. Of all the countries in the world, in the entire history of the human race, the UK is the most regulated ever. That still begs the question of what is the fail safe technology which the regulators must look for?
The answer is quite simple; use only a drilling fluid which is completely environmentally friendly; then it does not matter if the vertical shaft leaks. Do such fluids exist? Well, at least one is licenced under the Water Supply Regulations for drilling through aquifers for human consumption which, quite literally, means you could drink it.
We do have to make a choice. There is a potential risk of a significant short-fall in power security and that might be very serious in consequences;; if and when, it is not just the lights that will go out. ;It is a question of a balance of risks and sensible, common-sense, independent monitoring.