Early in February, smoke rose over Parliament Square. The occasion was a demonstration against the supposed dangers of hydraulic fracturing, or fracking, of underground shale formations to release reserves of gas. The smoke came from a device illustrating flaring of gas from the wellheads.
It was a misleading exercise, because no release of pollutants to the atmosphere is permitted during onshore hydrocarbon production. Onshore shale gas production would not involve flaring – the exceptions being a limited amount during exploration or a mishap during production.
These facts are pointed out by Ken Cronin, chief executive of UK Onshore Oil and Gas, which represents 60 companies involved in the search for onshore hydrocarbon resources. He says there is nothing unusual about the use of fracking within the UK. It is routine and has been employed at 200 onshore sites, mainly over the past 30-40 years.
The technique involves pumping fluid and small silica sand particles at high pressure into a shale formation. The liquid widens fissures in the rock which the particles then hold open, allowing the hydrocarbon to flow out.
The procedure required to access shale gas is in principle no different from that used previously, says Cronin. What is different in the case of shale gas, though, is the depth at which fracking will be carried out – 2,500-3,000 metres below the surface compared with 1,000m for ‘conventional’ sources – and the higher volumes and pressures for the fracking mixture injected into the wells to make the gas flow.
Exploitation incentive
UK gas consumption is 3 trillion ft3 (85 billion m3) per year, of which 50% is imported – a proportion that is set to rise to 75% by 2030 unless more domestic resources can be exploited, says Cronin. Gas combustion generates 30% of electricity consumption on average, although that figure can increase to 50% depending on weather conditions, so there is an incentive for exploiting shale gas reserves, he says.
However, the challenge is as much one of changing public perceptions of the technique as of implementing it. That was the sub-text of an event organised by the IMechE later in February, just around the corner from Parliament Square, and at which Cronin was a speaker – UK Shale Gas 2016: The Engineers’ Summit.
One supposed threat that fracking presents is to the safety of water supplies. That issue was addressed at the event by John Dewar, director of UK-based gas exploration and development company Third Energy. The firm is waiting for approval to carry out hydraulic fracturing at its vertical well KM8 at Kirby Misperton in North Yorkshire, which was drilled in 2013, to ascertain whether shale gas known to be present could be recovered economically.
Dewar says he has become concerned by the “myth and misinformation” over fracking’s supposed hazards. Much of this is based on extrapolation from the US, whose patchwork of regional rules is more lax than those in the UK, he says.
This negative publicity particularly applies to the possible contamination of water supplies, whether by fracking fluid or by the gas itself. Dewar believes the integrity of well design in the UK, coupled with safeguards in the fracking process, make the probability of groundwater contamination extremely low.
A starting point, he says, is to differentiate between groundwater and aquifers. The next step is to recognise that the UK regulatory regime makes no such distinction, and that companies involved in onshore hydrocarbon extraction must aim for zero transference of contaminants into adjacent water resources, irrespective of potability.
It is also necessary to realise that drilling creates a series of bores of decreasing diameter the deeper they go, each surrounded by a steel shaft lining coated in cement and extending back to the surface. At its upper level, the shaft will be lined by multiple concentric jackets of steel and cement.
So what are the possible routes by which groundwater could be contaminated? Dewar says there are three: directly through the intervening geology, horizontally through the well bore, and vertically through a faulty cement layer.
The potential hazards presented by the first two routes are, in effect, non-existent, he says. On the first count, he cites research by a consortium called ReFINE, led by the Universities of Newcastle and Durham, that focuses on fracking. It found that, apart from one exceptional case in the US when a hydraulically stimulated fracture propagated a vertical distance of 588m, the probability of such a fracture extending a greater distance than 350m is just 1%.
Minimal hazards
The relevance of that is that the UK Infrastructure Act of 2015 makes fracking at depths of less than 1,000m illegal, and that permission from the Department of Energy and Climate Change is required even for fracking at greater depths. Also, fracking in designated protected groundwater source areas is not allowed, whatever the depth. UK resources of potable groundwater are generally located well above that 1,000m benchmark – 200m being the usual maximum depth.
Meanwhile, the prospect of contamination through the walls of a well at groundwater level is implausible, because of the multiple layers of steel and cement with which the bore is lined in its upper reaches. The well design, he says, is “inherently safe”.
That leaves only the third potential scenario of a vertical flow of contaminant up through a faulty cement casing. That is at least a theoretical possibility, says Dewar, although it would require the integrity of the material to be compromised continuously along its entire height. Even just 2m of properly applied material would constitute an effective barrier.
But the methodologies for applying such casings, and for monitoring their integrity using sensors that enable the compilation of a ‘cement bond log’, are well-established, he says. His estimate of the chance of such a mishap occurring during fracking, assuming the well is properly designed and constructed, is just 1 × 10−13.
Cronin’s and Dewar’s words were corroborated at the event by Ken McIntosh, an independent engineer with North Sea oil and gas experience. He confirms that fracking is an established offshore technique, and that standards for well design and testing in the North Sea provide a template for land operations.
The offshore industry operates to a ‘two-barrier’ principle, he says. When translated onshore, at groundwater level a well would have at least two independent and independently testable barriers between the gas flow and surrounding geology. A steel layer with a cement jacket would be counted as just one.
Meanwhile, an important step towards ensuring consistent standards for well integrity onshore and offshore has recently been taken. UK Onshore Oil and Gas has come to an agreement with the broader-based Oil & Gas UK, which also includes offshore operators, to merge guidelines on the issue. So there will be no question of onshore shale gas recovery operations falling short of the standards established in the North Sea.
But that still leaves open the question of reassuring the public that the smoke that rose over Parliament Square was, in effect, without fire.
There are applications in or appeals for 11 locations in the UK for shale gas exploration, says Cronin. A good deal of work is taking place to assuage the concerns of nearby residents. He is confident that the industry will develop, provided it puts its case
across at grassroots level. Ultimately, he says, “this is about local planning and decision-making”.