A quick geology reminder. (Skip the first part of this post if you don't need reminding.)
Oil and gas come from dead stuff that dropped to the bottom of a murky sea and got buried, deep, long ago.
To get the hydrocarbons (that's oil and gas) you need a source rock, a reservoir rock and a cap rock.
The source rock was the mud the dead stuff fell into. It tends to form thick layers of mudstones, shales and clays, sometime thousands of feet thick. It's here that the organic material breaks down and is converted into liquid oils and gas. From the source rock it can, very slowly, migrate to:-
The reservoir rock is a porous rock, usually a sandstone or limestone, in which the hydrocarbons can accumulate so long as their escape is prevented by:-
The cap rock is an impermeable rock such as clay or salt that traps fluid hydrocarbons below it, trapping them until someone drills a hole through it to let it out.
'Conventional' oil and gas are thus obtained from the reservoir rock. You 'just' drill a hole through the cap, into the reservoir and watch the oil gush out. (It's a bit more complicated than that but that'll do for now.)
Now that we are at or past 'peak oil', the time when conventional oil production rate is at its maximum, the price has become high enough, at over $100 per barrel, to make it worth while considering obtaining oil and gas by 'unconventional' means. That means 'fracking' or fracturing the source rock so that it becomes a bit more permeable and releases the gas within.
Remember that every oil or gas reservoir must have (or at least must have had) a source somewhere below it. If there's a reservoir, there's probably shale with gas in it some way below. Remember that - it's important.
Fracking has hit the news recently, what with the fear of it reaching Balcombe in Sussex. Cuadrilla have planning permission to drill an exploratory hole in their search for, they say, conventional oil. Some folk think they might try fracking later on. They say they want to get at the oil in reservoir rocks in the Upper Jurassic. But, as we remember, where there's a reservoir there's a source below, and the big source is lower down in the Lias. To get gas from down under it will need fracking. Maybe that's the long term goal of Cuadrilla, after all, fracking is what they do.
A bit further north, in Surrey, Europa Oil and Egdon Resources have just won a case in the High Court overturning a decision by the Planning Inspector to uphold a decision by Surrey County Council to refuse planning consent for an exploratory well to be drilled in the Holmwood Prospect. Again, the stated plan is to drill for conventional oil with no mention of fracking the underlying source shales.
Also last week, in Leicestershire, Egdon Resources was granted planning
permission to drill for oil in the Carboniferous rocks. There's no mention of fracking; they say they intend to
exploit conventional oil in a fairly shallow well. But this area, in the
Widmerpool Trough, is underlain be about 2500 metres of shale source rock that is
judged by the British Geological Survey to be likely to contain gas. It's part
of the same Bowland-Hodder Formation in which fracking is proposed in Lancashire.
Last week's planning decision might be regarded as a first step, a Trojan
horse, to fracking in Leicestershire.
It's a similar story in Lincolnshire where Egdon (again), along with Union Jack Oil, are hoping to drill at Biscathorpe. They say they are going for the conventional oil in a fairly shallow well. And so they may well be. But further down there is 2000, perhaps even 3000 metres of Bowland-Hodder shale in the Gainsborough Trough, a deep basin of sedimentation. The potential for fracking to obtain gas is all too obvious.
Further east, just east of Louth, there's a small oil field at Keddington. It has been producing, on and off, a little oil and gas for many years and plans are afoot for further drilling to obtain more of this conventional oil. Egdon Resources operate this site too. And of course there's shale below. Further east still, we have an area again licensed to Egdon around North Somercotes. This is a little different as there does not seem to be much conventionally trapped hydrocarbon, though the area is probably the source for the gas that has already been extracted from the Saltfleetby/Skidbrooke field. Fracking may be the only option to exploit the North Somercotes Prospect.