Fracking for Gas: The Real Problem

Perhaps the novelty of fracking (hydraulic fracturing) shales for gas has led to an instinctive suspicion of the technique, without there being careful enough consideration about what the real problems are. Groundwater contamination is frequently mentioned as a potential hazard but legislation can simply be used to make sure the additives are environmentally benign. All aspects of the drilling, from planning to production, are covered by current, stringent drilling and environmental legislation honed by the experience of hundreds of onshore wells. Also the long-term visual environmental impact is most unlikely to be anything like that of wind turbines, currently despoiling our green and pleasant land.

Fracking is not, in itself, a process we should be intimidated by. However, there is a more indirect effect that we should be concerned about. This is when the fracture pattern created by the fracking intercepts, and introduces water into, natural fractures and particularly faults, so-called when the rocks either side of a fracture are displaced. Faults tend to be under stress, and water has the effect of reducing the friction between each side of the fault, in effect lubricating it and making it much more likely to move, causing earthquakes. These could be quite substantial, depending on the size of the faults intercepted by the fracking. In fact the company Cuadrilla suspended its shale gas test drilling near Blackpool, Lancashire, in June 2011 amid fears that the fracking was linked to earthquakes of 2.3 and 1.4 on the Richter scale that hit the Fylde coast. They had likely intercepted a natural fault system, and despite Cuadrilla’s insistence that it was due to an “extremely rare” combination of factors, faulting in the subsurface is very common indeed.

However, the good news is that technically it’s rather an easy problem to solve. Seismic reflection surveys could accurately identify the natural fault patterns, so the fracking process can avoid them. The problem is, unless there’s a survey already in the area of the fracking (from a previous, conventional oil and gas exploration effort), they’re fairly expensive to acquire and could impinge on the economics. To understand why this is so requires a brief account of fracking, and why the economics are very different from those of conventional oil exploration and production. The account below makes no distinction between fracking for shale oil or gas (both referred to as hydrocarbons), as it’s effectively the same process.

In fracking, a well is drilled into the oil or gas shales and high pressure water is introduced into the shale formation which results in fractures. Formed of fine grains, shales are a really poor repository for oil and gas as there’s no visible space, or porosity. Fracking opens up spaces in the shales where the very thin and disconnected smears of gas or oil from between the shale layers could drain into. The aim is to produce the greatest density of fractures within the largest volume to access the most hydrocarbons. Unlike harder and more brittle rocks such as sandstones, shale is more elastic and fractures tend to close up if the pressure is reduced when the water flows back after treatment. Sand, or synthetic equivalents, are added to the water and remain to keep the fractures open.

The reason shales behave in the way they do is because they’re formed of thin layers of consolidated, fine-grained mud and clay, originally accumulated at the bottom of lakes or the sea. This immediately raises the question of how the hydrocarbons managed to get there in the first place. In fact, in one form or another, they’ve always been there. The mud would have comprised organic material falling into it from the water column, be it dead animals or plants. With the weight of the overlying rocks and the higher temperatures at depth, chemical processes would have converted this original organic material into hydrocarbons. This is a similar process to that seen in the larger rubbish tips where build-ups of methane gas are frequently flared off.

Such shales were, in fact, the source rocks for conventional oil and gas fields. It’s widely accepted that the great forces that formed the Alps in the mid Miocene time (about 12m years ago) and raised Britain and Western Europe from beneath the waves to form land, were also responsible for squeezing the oil and gas out of the source shales and into porous rocks, for example sandstones. With a favourable juxtaposition of non-porous rocks – like the shales themselves – oil and gas could have been trapped in porous rocks, forming the conventional and familiar oil and gas fields.

To put into context the difference in production between a fractured oil shale well and a conventional oil well from, for example, a sandstone oil field, the former would typically produce less than 10 barrels a day; a reasonable well in a conventional oil field could produce literally thousands of barrels a day: similarly for gas. Gas generally flows better than oil from fractured shales to the extent that generally over the same period, more energy can be obtained from the output of gas fracking, all things being equal. Despite this, it’s still not certain if fracking in the UK is economic at current prices and without a very local market for the gas, for example a gas-fired power station built adjacent to the well site to save on transportation costs. Even then, a large number of expensive wells could be required to maintain the kind of production needed for such a facility.

Seen in the context of the fragility of the economics, it’s hardly any wonder the companies currently involved in fracking would sooner not address the problems of potential earthquakes caused by high pressure fluids entering the natural fault system. That’s despite the fact that there’s a simple and effective solution, albeit rather expensive. Such a problem in countries like Australia or the United States, where fracking is conducted in areas well away from urban communities, wouldn’t have anything like the same effect as in the more densely-populated UK.

It’s good to see that the recently-formed Oil and Gas Authority, handling the new applications for fracking licences are strongly encouraging new applicants to include seismic surveys.  With proper safeguards there’s no reason why fracking shouldn’t go ahead in the UK, providing those safeguards include seismic surveys if one doesn’t already exist or hasn’t been planned in an area targeting for fracking. Relative to the potential damage of an earthquake, it’s a small price to pay.

So the burning question of the day is; with the appropriate safeguards, should fracking for gas go ahead in the UK?