- In order to place some perspectives on social and environmental impacts of shale gas developments I have built a gas model for the UK.
- The model is based on a type shale well with 3 million cubic feet per day initial production declining 33% in year 1. This is an optimistic guess based on production history data for more productive shale plays in the USA.
- Drilling 100 such wells / year for 10 years may employ 17 drilling rigs and would stabilise UK gas production at around today’s levels.
- Drilling 200 such wells / year for 10 years would see production growing to 2.7 tcf per annum and the UK may once again become self sufficient in natural gas.
- There are huge uncertainties in these estimates. The Bowland shale where most hopes are pinned may turn out to be a dud. Productivity could be higher or lower than my assumptions. If productivity was 25% of my guesstimate and declines higher, 1000 wells over a decade could easily rise to 5000 wells for the same production. It is extremely important that the UK gets some real test data from exploration wells to delineate what the real prospects are.
Figure 1 The distribution of the Bowland-Hodder shale in England. The areas in red delineate land where the shale is present at depth in the sub-surface .
The British Geological Survey have published a detailed and competent report on the potential of the Bowland-Hodder shale, the highlights of which are summarised below . It needs to be stressed that without test data from at least 10 to 20 exploration wells it is impossible to assess the potential with any certainty. It may turn out that Bowland is a super rich shale to rival the Marcellus of the USA, or it may turn out to be a dud like the recent Polish experience. Shale plays are also non-uniform and tend to have sweet spots that can only be identified through quite extensive exploration drilling. The main focus of this post is to try and place the uncertain potential into a perspective for what this may mean for the UK in terms or providing energy security and the potential for environmental and social disruption.
What is shale gas?
Gas shales are fine grained, tight rocks that contain mature organic matter that has been converted to gas (or oil in the case of shale oil). Not all so-called gas shales are shales; some are limestones and some are tight (impermeable) sandstones. The lack of permeability means that gas or oil is trapped in the rock that needs to be hydraulically fractured (fracked) to liberate its prize. Organic matter may comprise plant material or marine organisms that when buried and subject to pressure, elevated temperatures and time, is slowly converted to oil and gas. This process is called maturation and very generally the hydrocarbon window may occur at depth of 10,000 ft at temperatures around 100˚C.
Potential of the Bowland-Hodder Shale
This account of the Bowland-Hodder Shale (Bolland Shale from here on) is based on the BGS report  that has a quite readable two page summary (link at end of this post).
The Bowland is a deep marine Carboniferous shale (318 to 347 million years old) that underlies much of northern England (Figure 1). It is extremely thick, locally up to 16,000 ft, which is much thicker than many of the N American shale plays. But the organic matter content is relatively lean at 1 to 3%, it would have been better had the thickness been half and the organic content double. Organic matter ranges up to 8% and it will be sweet spots like this that companies will look for.
The BGS estimate that the Bowland shale will be in the “gas window” below 9,500 ft. That is, once it has been buried to this depth, some of the organic matter may have been converted to gas. But the picture is made more complex by the fact that some areas have been uplifted, hence gas bearing shales may be encountered at shallower levels.
There was also a natural build-up of methane in the Wyresdale Tunnel, Lancashire, which lead to the fatal Abbeystead explosion in May 1984.
The Bowland Shale has Upper and Lower units. There is more data for the Upper, but the Lower potentially contains a lot more gas. The RESOURCE estimates are shown in Figure 2. With a range of numbers, the one to focus on is the P50 estimated total resource of 1329 tcf (trillion cubic feet; that is the mid range estimate). Compare that with the total production from the North Sea to 2012 of 86 tcf. The shale gas estimated resource is vast. The resource is the amount of gas believed to be in place. The reserve is that part of the resource that can be developed commercially and the numbers here are much smaller with a guesstimate of 4.7 tcf. As we shall see below, that sort of recovery level will make little difference to the UK’s lamentable energy status.
Figure 2 Resource estimates for the Upper and Lower Units of the Bowland-Hodder shale .
UK shale gas production perspectives
I wanted to try and place “the hype” around UK shale gas into some form of perspective. Without test data from exploration wells, this is quite impossible to do with any meaningful certainty. But here goes…
Based on US production experience (Figure 3) I have modelled what a UK shale gas well production profile might look like if the Bowland shale is as productive as the good US shale plays (Figure 4). I have then assumed that armed with successful test data like this, the UK goes on to drill 100 shale wells per year for 10 years. How much would this contribute to national gas production?
Figure 3 Average production profiles for shale gas wells in the USA . Note units are million cubic feet per year.
Figure 4 Based on the data in Figure 3, if the UK gets lucky, a well may produce 1000 million cubic feet per year in its first year translating to about 3 million cubic feet per day at the beginning of year 1. Modelled decline rates are shown as percentage values. Shale wells decline extremely fast in the first years of operation and then decline slows in the tail. I’ve been advised that the rather steep declines I have used here could even prove to be optimistic. This is all guess work and reality may turn out to be very different.
Figure 5 Assuming that 100 wells are drilled per year, the production stack after 10 years, when 1000 wells will have been drilled, takes on this shark fin shape that is characteristic of shale provinces. Each slice represents production from 100 model wells as depicted in Figure 4.
The result is shown in Figure 6. Drilling 1000 shale wells between 2016 and 2025 would stabilise declines from conventional gas creating a production plateau of about 1.5 tcf / annum, compared with current consumption of around 2.8 tcf / annum. This outcome would significantly reduce UK future dependency on imported gas (Figure 6) but would still leave us importing about 50%.
Figure 6 Historic UK conventional North Sea gas production (BP) amounts to 86 tcf, 1970 – 2012. The projection includes a 10% decline which is the historic average. Without shale gas, conventional gas will have declined to near zero come 2025. The 100 well / year model (Figure 5) would stabilise UK production at about today’s levels. The 8.2 tcf production estimate is more than double the BGS guess for reserves but is still tiny compared with the size of the resource.
Being reasonably impressed by the outcome of drilling 100 shale wells / year I built a second model simply doubling the number of wells to 200 / year. This lifts UK production to about 2.6 tcf / annum by 2025 in which case we would once again achieve self sufficiency – a very big prize worth going for!
Figure 7 Doubling the drilling rate to 200 wells / year would see UK gas production growing significantly, potentially towards a point where we were once again self-sufficient.
If this sounds too good to be true then there has to be a catch. The 100 well / year model contains 8.2 tcf of production, roughly double BGS reserves guesstimate. The 200 well / year model contains 16.5 tcf of production. The bottom line, without exploration and production history data this is all guess work. Zero production by 2025 is probably just as likely as 16.5 tcf and vice versa.
While the USA is turning out shale gas wells faster than Henry Ford turned out Model Ts the pace is likely to be more sedate in rural England. Let’s imagine it takes a rig 2 months to drill a well, this will dictate the pace of development. That would mean 17 drilling rigs operating round the clock to turn out 100 wells per year. Most of the population living in cities would notice nothing. Many rural populations would notice something once in a while and may grumble when there was a drilling operation near by, but then after a short while, the drilling and fracking crews move on. Landlords would celebrate as highly payed drill and fracking crews moved around the country.
17 operational rigs doesn’t sound a lot spread over a large area. To move up to 200 wells / year would mean 34 rigs. If the production results are lower than my model well, expect more rigs and less profits, if the production results are higher, proportionally less. Uncivil unrest that disrupts drilling operations and slows them down will increase the number of rigs required that would add to the social impact. One final point, the Bowland Shale is so thick, a single vertical well could potentially have several horizontal laterals off it meaning that the number of drill sites could be substantially reduced.
One concern with shale gas and fracking operations is the contamination of sub-surface drinking water supplies by drilling fluids, fracking fluids and gas. A study of drinking water wells in Pennsylvania did find a correlation between methane levels in drinking water and proximity to shale gas wells . About a dozen wells were found to have gas concentrations above 30 ppm, the threshold to take action to mitigate the problem.
I believe it is the case in northern England that most drinking water supplies are drawn from surface reservoirs. Society as a whole needs to weigh small and manageable environmental risks against the potential strategic importance of shale gas to the UK economy and national energy security. There are environmental risks associated with all forms of energy “production”. We either accept these risks or sit at home shivering in the dark.
It is vitally important that companies are encouraged and enabled to conduct comprehensive exploration of shale gas resources in the UK in order to evaluate potential contribution of this energy source to the future UK economy and energy security.
If the UK gets lucky and the Bowland shale turns out to be as productive as the good US plays, then 2000 wells by 2025 may once again see the UK achieve self sufficiency in natural gas supplies.
Other shale gas posts
1. Andrews, I.J. 2013. The Carboniferous Bowland Shale gas study: geology and resource estimation. British Geological Survey for Department of Energy and Climate Change, London, UK. Link here.
2. EIA Annual Energy Outlook 2012
3. Robert B. Jackson et al 2013, Increased Stray Gas Abundance in a Subset of Drinking Water Wells Near Marcellus Shale Gas Extraction: www.pnas.org/cgi/doi/10.1073/pnas.1221635110 Link here.