I caused a minor twitter ripple last week after claims I made in the House about the number of wells that might need to be drilled across the UK to achieve various stated ambitions for shale gas recovery.
I’ve checked back on the Hansard record for last week, and I think it’s fair to say that , during a brief speech I was not crystal clear about what the figures I set out referred to . So here’s the clarification. Although having said that, the clarification will also inevitably be a bit vague, because we have only very general estimates about how much shale gas there may be in the UK, how much of it is actually recoverable, and how any wells drilled in the UK might perform in practice. We do, however, have some data about well performance and lifetimes from the U.S, but even then we need to be a bit cautious about transferring this directly to the scenario here in the UK. What we also know from the US is that, individually, shale gas wells do not produce much gas compared with, say, a North Sea gas well. Nor do they produce gas over a very long period either; they deplete on a steep curve after the initial fracking has taken place.
Some shale gas propagandists will quote selectively from very well performing wells to make their case, but if we are producing over a large area, and over time, we need to be much more measured, and take averages on performance and life of different wells in different places as our yard sticks. I’ve previously quoted some 2009 work on well lifetimes. There seems to be a reasonable level of agreement that their economically productive lives are about seven or eight years in length.
There is less agreement on what an average range of lifetime production might be. The work I looked at suggested an average of about 0.81 bcf (billion cubic feet) of gas extracted per well but the US Geological survey can be cut several ways. Looking at the general averages gives about 1.25 bcf per well, a recent UK Institute of directors report (funded by Cuadrilla) came up with an improbable average production per well of 3.2 bcf.
So I’ve taken a low average and a medium average as my estimate points – the 0.81bcf, and point double that (1.62bcf per well) – more than the US geological survey average, but half the IoD sum.
So how might those figures translate into possible well numbers when set against recent claims?
Claim one is that we should aim to exploit about 10% of the shale gas resource under the ground in the UK. That 10% would probably then be based on the British Geological society’s estimate of what reserves are in the Bowland shale in the North of England, where most of the richest seams are located , plus some lesser reserves elsewhere in the Country. BGS estimates that there is about 1300 trillion cubic feet in the Bowland shale, so let’s say there may be another 500 tcf elsewhere in the country, making a 10% recovery of the total resource about 180 tcf. On my medium estimate of lifetime well output that comes to about 110,000 wells. And that is the basis of my claim in Parliament that this would be the sort of range (I suggested 100,000 to 107,000) of wells that we would need to anticipate being drilled across the UK. This would perhaps be an average of about 160-170 per constituency, but clearly higher in those areas with rich gas seams underneath them such as Yorkshire and Lancashire. The lower average figure would of course mean about twice as many wells needing to be drilled.
Claim two is the more modest aim of providing some sort of underpinning to the UK’s gas demand over a period, perhaps 10% of the total. This would require far fewer wells to be drilled, but still a substantial number. UK gas demand per annum comes to about 3 trillion cubic feet, so if the ambition was to substitute 10% of UK gas supplies with shale for a 50 year supply period, about 15 tcf would need to be recovered – the job of about 18000 wells on my lower output, and 9000 on my higher average output. These wells, as I pointed out in the Parliamentary debate, would be grouped into double, football-pitch-sized ‘pads’ perhaps containing six wells each. This would mean a ‘lowest case’ scenario (10% UK gas requirement higher output per well) of about two pads per constituency to a barely imaginable ‘highest case’ scenario (10% exploitation of overall reserves, lower average estimate output per well) of fifty or more pads per constituency. My estimate in Parliament of 18 pads per constituency was somewhere between the two.
What ought to be emphasised, in concluding all this, is that not all these wells would be drilled at once, which is sort of good news. Except that shale gas in production would not look like Wytch Farm in Dorset, where a quiet nodding donkey extracts oil from a drilled well over a long period of time. There would need to be, in order to maintain a supply, fairly continuous redrilling, with attendant trucks, water, chemicals and so on in areas where there are reasonably exploitable reserves.
No doubt this expanded and more qualified estimate will bring down a little more opprobrium on my head but the bottom line is this: any serious level of shale gas exploitation in the UK will inevitably bring about something like the numbers of wells I’ve set out here. The exact number will depend on the degree of ambition. And if we are to press the button on shale gas, that is what we need to accept as a consequence. Whether we conclude that it’s worth it for what we might get out of the ground, or whether we decide that there are alternative, lower carbon ways of proceeding is what should now be seriously debated between us.