Readers letters
I read with great interest your report on “Fracking, no threat to water supply” in the January edition. It is high time that the subject of hydraulic fracturing to exploit potential shale gas reserves is raised into a balanced and intelligent debate. There has been considerable scaremongering put about in the media and it’s time to start setting the record straight on an issue of such potentially massive national interest.
Firstly, let’s address the context in which there is a need for the UK to determine if it has commercial shale gas reserves. Over recent decades, the UK has been self-sufficient in meeting its gas needs. In the 1990s, the move from coal to gas fired electricity generation as a consequence of North Sea gas production reduced the UK’s carbon emissions by more than any other European country. However, North Sea production has reached its peak and industry forecasts estimate that the UK will need to import around two thirds of its gas by 2020, or replace it with alternative energy sources. Consequently, the Labour government of the last decade decided to implement an energy strategy to ensure that the UK would keep the lights on in 2020 and beyond without being at the mercy of imported Russian gas. This strategy was essentially three-fold. Firstly, a liquefied natural gas (LNG) terminal was built in Pembrokeshire to import gas from the Middle East. Secondly, the public were warmed up to the idea that nuclear power would be developed further with a new breed of modern reactors being built. Finally, the government would subsidise renewable energy projects to the tune of around £200 billion over the period to 2020. This pledge was made before the financial crash of 2008 and the Japanese tsunami of 2011.
The US was facing a similar situation and had also started building LNG terminals for imported gas. However, a massive sea change has happened in the last decade following the commercial extraction of gas from shale. In just a few years, the whole gas dynamics in the US has fundamentally shifted, with around 25% of entire US gas consumption already produced from shale. The gas price has more than halved as a result and the LNG import terminals are now being converted to export.
What is shale gas? All conventional natural gas is derived from source rocks, where sediments were gradually deposited together with organic material millions of years ago. If heated and pressurised in the subsurface to a level within a certain “maturation window”, gas is created. This gas permeates through porosity in this subsurface (fractures, or pore spaces between the grains of rock) and becomes trapped when an impermeable layer of rock prevents further transit by the gas. This then builds into a conventional gas reservoir and can often be some distance from the original source rock. Shale gas is simply the gas that is trapped in its original source rock, because the grains of silt that the shale is made of are so small that the pore spaces will not allow the movement of the gas, nor has there been any fraulting to allow such transit. For this reason, wells that have previously been drilled into shale gas deposits have been sealed up as the gas wouldn’t flow into the well.
However, conventional gas wells frequently encounter “tight” reservoir rocks, where the gas flows very slowly into the well because of poor porosity and permeability. This problem was first solved in 1948 with a technique in which a pressurised fluid was injected down the well, together with course grained sand, at such high pressure that it caused hydraulic fracturing of the rock in the reservoir. When the fluid pressure was lowered and the fluid recovered to surface, the fractures created were held open by the sand that had been injected, thereby improving the permeability of the reservoir rock. This “fracking” technique has subsequently been used all around the world, in many thousands of wells, including onshore and offshore UK. Why should fracking into shale suddenly be deemed new and controversial when the practise has been so widely used for decades?
Fracking proved successful in tight conventional reservoirs, but did not appear to work for the shale source rocks. Determined to solve this, Mitchell Energy trialled a number of process and, around ten years ago, successfully delivered gas from the Barnett Shale in Texas after trialling different techniques since the 1980s. The wells drilled are horizontal, in that the wells were drilled vertically down by two or three kilometres then horizontally out by a similar distance along the shale. The fracking was then performed in this horizontal section.
The unexpected success of shale gas extraction has opened a new and massive source of energy. Cuadrilla is the first company to successfully produce gas from shale in the UK. They have also published a report that estimates the volume of gas reserves in-place under their Lancashire exploration licence to be around 200 trillion cubic feet. To put this in perspective, even if only 10% to 20% of this volume is extracted, the quantum would equate to around ten years of UK demand.
Some members of the environmental lobby have seen this as a threat to the pursuance of wind and other renewable energy projects through the loss of the £200 billion government subsidy that was promised. Consequently, scare stories are being thrown into the media to try to nip public opinion in the bud before shale gas exploration gets started. Film footage from the US film “Gasland” of gas being ignited as it comes out of the kitchen tap has been widely spread, yet has been proven to have no connection whatsoever with shale gas fracking; the claim being that fractures are penetrating into the water table. The fracking is taking place around 2 kilometres beneath the water table, with fractures that extend only tens of metres. Lately, two “earthquakes” in Lancashire have been blamed on fracking. These tremors registered 1.9 and 2.3 on the Richter scale, which is about the level felt inside the house when a car pulls up on the drive outside; a level that is barely detectable unless in a high rise building.
We need to have an informed debate about the pros and cons of shale gas development, but before that we also need to determine if shale gas can be extracted in the UK in commercial quantities. It’s time for the professional engineers in this country to take a look at the facts behind the fracking process and contribute constructively to the debate. We could displace coal-fired electricity generation with gas-fired generation and still meet our 2020 carbon emission targets. Time is of the essence. We are on the verge of importing trillions of cubic feet of gas and we may not need to.
Robert Wilde, Northampton
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