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Environmental Impacts Of Drilling For Geothermal Energy

November 9, 2018

By Paul Homewood


h/t Joe Public




We were discussing the geothermal project in Cornwall the other day, and questioned the similarities between geothermal (good), and fracking (bad).

Cornwall County Council have actually published a fact sheet for geothermal, which outlines potential environmental issues:


What are the environmental impacts?
Generally the environmental impact of geothermal developments is extremely low. There are virtually no emissions and land use and visual impact are small. However, some potential impacts do need to be considered and information on each of these issues is set out in the sections below.
All these issues will be fully considered as part of the planning process. Cornwall Council has worked with the industry to develop robust Supplementary Planning Guidance to ensure risks are mitigated and minimised. In addition to planning permission, projects must also obtain the necessary licenses from the Environment Agency.

What is the risk of earth tremors (induced seismicity)?
The development and operation of the deep geothermal system will require the injection of water under moderate pressure. This process will cause some natural fractures to move slightly,
by perhaps a few millimetres, causing what are referred to as ‘microseismic events’. This is inevitable and expected.
These events can be detected and located with highly sensitive instruments and their distribution can be used to help understand the extent of the reservoir.
The vast majority of these events will be far too small to be felt at the surface but it is possible that some will be, with some minor vibrations perhaps comparable to the mining blasts that were felt when the tin mines were in operation.
In order to ensure that geothermal development does not create an unacceptable risk of seismic activity, as set out in the Council supplementary planning guidance, a seismic hazard assessment should be undertaken that considers: pre-project seismic activity, the likelihood of triggering an event and measures to avoid it. Ongoing monitoring throughout the lifetime of the plant will be adopted and maximum acceptable levels, as imposed by the Council, should not be exceeded.
When looking at the risk, the earthquakes of at the Basel project in Switzerland are often mentioned. The geology in Basel is very different to Cornwall’s: Basel is situated in an unstable tectonic region with a long history of earthquakes.


What impact will it have on water?
During the drilling and development stages of the project, a large source of fresh water will be required. The Council’s Supplementary Planning Guidance advises, as far as possible, that drilling and stimulation fluids should be re-used in order to reduce freshwater resource impacts and potential disposal issues. Drilling and stimulation fluids not reinjected should be stored in tanks, with appropriate spill protection.
During operation the water requirement will be minimal, perhaps zero. This is because the water will circulate in a closed loop; down one well and up another and the reservoir will be operated at zero water loss as far as possible. Each of the wells will be steel lined to considerable depth and therefore there will be no risk to ground water supplies. Any water produced during testing will be contained, treated if necessary, and disposed of in an environmentally sensitive manner.


Will there be increased traffic or heavy plant to the site?
Normal day to day traffic will not add significantly to the existing levels on the industrial estate.
The main impact to the local transport network will be during the mobilisation and demobilisation of the large drilling rig, each of which will involve HGVs transporting equipment on and off the site over a few days.
A traffic management plan may need to be prepared and agreed with the Council in order to avoid unnecessary local traffic disruption during this time.

How noisy will the drilling be?
It will take around 6 months to drill the two wells. For both engineering and financial reasons drilling will take place 24 hours a day, 7 days per week. There is therefore a potential for noise nuisance during the night.
The Council’s Supplementary Planning Guidance sets out the noise limits for different proximity to receptors and states that developers should demonstrate throughout the construction, operation and decommissioning phases of a deep geothermal development, all practicable measures will be taken to minimise noise emissions.
Noise will be one of the most important criteria used to choose a drilling rig. Rigs designed specifically for use in populated areas and urban environments will be favoured. Further noise reduction measures on the site boundary will be put in place if required.
The power plant will be small and will be designed with the specific site location in mind. Detailed planning permission will be required for the plant and will be subject to noise limits. Different plant types have different noise characteristics; Water-cooled power plants are extremely quiet whereas air-cooled plants have some fan noise (but are currently used in European power plants operating close to residential areas).


What is the risk of radiation from the granite?
Radon and background radiation is naturally produced by the granites and clays of Cornwall. The radioactive decay is the reason the granite is heat producing.
During drilling the level of radon emitted is not considered to have a significant impact and water quality will be monitored and carefully managed.
During operation, all water will circulate in a closed circuit so radon gas will not be emitted. Longer term, any build-up of radioactive minerals will be safely removed from site and dealt with.



What is the visual impact?
During the drilling phase, the drill rig will be visible from outside the site. It is likely to be 25-30m high. Lighting will be arranged to minimise light pollution and nuisance at night.
Geothermal power plants have a relatively small footprint on the landscape, and don’t require the storage, transportation, or combustion of fuels. Air-cooled plants are quite unobtrusive. The structure of water-cooled plants is also unobtrusive but water vapour plumes would be visible under some weather conditions.
Site selection, design and layout can minimise the visual impacts of all development. This is considered in detail in the Council’s Supplementary Planning Guidance with specific consideration given to tourism, designated and protected areas, ecology, open areas, the character of an area and the views of nearby residents.


What is the difference between EGS and ‘fracking’ for shale gas?
Before considering the process it is important to understand the benefits of geothermal energy; it is a clean renewable technology that emits very little gases and does not contribute to an increase in greenhouse gases and climate change. With the Council’s involvement, the benefits from locally generated heat and power can be kept local.
The process to enhance the water flow in the granite is similar to the ‘fracking’ process used to capture shale gas. However, while both processes have the potential to create seismic events (tremors), the geothermal process takes place at far greater depths 4.5-5km as opposed to
1.5km for ‘fracking’ and with lower pressures, so surface vibrations are less likely to be felt. There are also some important differences between the processes:
Fracking for shale gas uses much higher pressures to initiate new fractures in un-fractured shale rock, which result in wide cracks that require additives (sand and chemicals) to hold them open. Only some of the fluid returns to the surface, where it is sealed in containers before treatment. Licences require operators to minimise the release of gases: when it can’t be economically used, natural gas must be ‘flared’ to reduce its global warming emissions and the gas may only be ‘vented’ – released into the air – when necessary for safety.
The process used to open and enhance pre-existing fractures in granite uses the rough surface texture of rock fractures to allow self-propping of open fractures, so there is no requirement for any chemical additives in the pressurised water: this reduces the risk of ground water contamination. This process takes place at depths of 4 km and deeper, where there is no natural gas or drinkable water present. During operation the water is circulated in a closed-loop: there can be no release of gas or minerals at the surface.


When you get down to basics, there seems to be little difference between the two processes. About the only issue of substance is that geothermal is said to go to greater depths.

However, as fracking also takes place well below the water table, it is not clear why this should make any real difference.

Also with geothermal comes the risk of radon contamination. Interestingly, Cornwall CC state that there will be no risk to water supplies as each of the wells will be steel lined to considerable depth. Fracking operations also of course are regulated to provide the same protection.

Otherwise, all of the “problems” that we hear cited for fracking are present with geothermal drilling as well:

  • Earth tremors (always labelled as “earthquakes” where fracking is concerned.
  • The need for large amounts of water during the drilling stages.
  • Increased heavy traffic for short periods at the start and end of the project.
  • Noise nuisance during the drilling phase.
  • Visual impact during drilling.

But as Cornwall CC point out, geothermal energy is a clean renewable technology, so its environmental impact does not matter!

  1. HotScot permalink
    November 9, 2018 12:00 pm

    I suspect the results of fracking (gas) can, if necessary, be contained and transported around the country. I also suspect it can be piped for many miles into many homes and businesses.

    Geo thermal is an acceptable local endeavour to access clean energy, I believe it can be utilised to run steam turbines to produce electricity but at what capacity? It presumably means a power station must be built very close to the geo thermal site, and how many geo thermal sites are available across the country?

  2. saparonia permalink
    November 9, 2018 12:18 pm

    We are an almost earthquake free country and we don’t have experience of earthquakes as they do in other countries. Small ones make big news here. We have a network of old coal mines beneath us and if the shale or geothermal rock is disturbed we have no idea of what effects it would have on the honeycomb beneath us. We are a small island in comparison to the vast fracking lands of the US where they have regular, daily earthquakes which are well away from areas of high population. It would be a serious mistake for this kind of activity here in my opinion.

    • martinbrumby permalink
      November 10, 2018 7:01 am

      Scaremongering baloney .
      You obviously have ‘no idea of what effects (fracking) might have. But you obviously aren’t a qualified and experienced professional.
      ‘The honeycomb beneath us?’
      Get a grip.
      Where is it proposed to drill through mining goaf and seal the lining?
      Of course, methane is quite commonly extracted, efficiently and profitably from old coal mine workings. But no-one cares about that.
      Shale gas extraction is the only current hope of keeping the lights on and the central heating working without relying on Putin and the Arabs. Paid for by private industry and with huge revenue benefits.
      But I guess you’d rather rely on the whirligigs.

  3. Hugh Sharman permalink
    November 9, 2018 12:36 pm

    @HotScot! As regards fracked gas, it will need to be treated to remove any hydrogen sulphide, CO2 and natural gas liquids before it can be burned. Before the gas enters the gas grid, it will also have to conform with the thermal and safety norms of grid gas.

    As regards gas emissions from geothermal sources, when these are volcanic in nature, as most geothermal resources are, the geothermal activities enhance emissions of both CO2 and H2S. I doubt there will be much of either in Cornish granite!

    Of course, to describe the almost imperceptible seismicity caused until now by fracking, as “earthquakes” is outrageous. Both HMG, for insisting on such a ludicrously low theshold for alarm and Cuadrilla for accepting these strictures, deserve equal blame for unnecessary and costly stoppages that might yet snatch away UK’s chances for reducing costly imports of gas.

  4. Ben Vorlich permalink
    November 9, 2018 12:39 pm

    What is the difference between EGS and ‘fracking’ for shale gas?
    Before considering the process it is important to understand the benefits of geothermal energy; it is a clean renewable technology that emits very little gases and does not contribute to an increase in greenhouse gases and climate change. With the Council’s involvement, the benefits from locally generated heat and power can be kept local.

    Any answer beginning “before considering” always implies there is no difference and is distraction tactics.

  5. November 9, 2018 1:13 pm

    The incredible weirdness of climate change impacts research

  6. It doesn't add up... permalink
    November 9, 2018 1:30 pm

    What’s this nonsense about no earthquakes in Cornwall?

    ML 1.4

    ML 1.1

    ML 0.3

    ML 0.9

    You’d have thought they were fracking already in Penryn

    A list since beginning of 2008:

    2009-04-11….50.194….-5.151….3.2….1.4…. STITHIANS
    2009-06-17….49.837….-4.885….6.0…1.3…. LIZARD POINT
    2009-10-24….49.452….-5.596….5.0…2.1…. LIZARD POINT
    2011-12-04….50.482….-4.872….3.0…2.2…. BODMIN
    2013-05-05….50.392….-4.618….4.5….1.8…. LOSTWITHIEL
    2013-07-02….50.135….-5.137….2.7….1.3…. FALMOUTH
    2015-05-14….50.504….-5.280….11.4….1.4…. NEWQUAY
    2015-09-27….49.981….-5.384….6.8….1.1…. MOUNT’S BAY
    2015-10-18….50.432….-5.071….6.6….1.0… NEWQUAY
    2015-12-04….50.565….-4.303….3.9….1.3…. LAUNCESTON
    2016-01-27….50.164….-5.120….1.5….0.8…. PENRYN
    2016-10-27….50.510….-4.533….11.1….2.3…. LISKEARD
    2016-10-27….50.516….-4.523….8.5….0.2…. LISKEARD
    2017-01-28….50.814….-4.673….2.6….0.4…. OFF BUDE
    2018-09-14….50.176….-5.114….1.0…0.9…. PENRYN
    2018-09-14….50.174….-5.115….1.0…0.3…. PENRYN
    2018-09-14….50.165….-5.108….1.0…1.1…. PENRYN
    2018-09-25….50.187….-5.083….1.0…1.4…. PENRYN
    2018-10-06….50.304….-4.889….2.3….0.6…. GRAMPOUND

    (Lat/Long, depth km, ML, nearest town)

  7. Joe Public permalink
    November 9, 2018 2:15 pm

    Remember the anti-frackers getting their knickers in a twist regarding micro tremors?

    How they had apoplexy at 2.3 tremor which did no damage (but in an absolute coincidence, maybe one teacup fell off an shelf)?

    Can anyone guess their reaction when they learn that geothermal fracking in Cornwall way generate a 4.0ML earthquake – one 50x bigger and 350x more stronger?

  8. It doesn't add up... permalink
    November 9, 2018 2:46 pm

    SW Water report:

    90% of our supply comes from surface water sources, such as reservoirs and river intakes. Local reservoirs are supported by three large strategic reservoirs: Colliford,Roadford and Wimbleball.

    The other 10%of our supply comes from groundwater sources such as springs, wells and boreholes and are mainly located in East Devon.

    This is different to other regions – for example, Wessex Water gets 75% of its water supplies from groundwater.

    So the water table may be less of a concern.

    A useful hydrogeological map of the UK:

    It seems that the part of teh Fylde where Cuadrilla re operating is not water productive, although there is an area closer to Preston that might be useable. HOwever, it should be remembered that United Utilities had a big payout and three weeks of getting Preston and area customers to boil their water because a surface reservoir became infected by a dead cow.

  9. dave permalink
    November 9, 2018 3:03 pm

    As with any well, the flow rate of the extracted substance (heat energy in this case) will decline rapidly as the pressure (temperature difference between the introduced water and the IMMEDIATELY surrounding rock) lessens. They will have to harness the heat from further away by fracturing the rock. “Fracturing the rock…” Oh that is sometimes called “fracking.”

    In granite they will have to use much more force. I do not see how it is even possible without breaking the main well.

  10. November 9, 2018 3:37 pm

    Cornwall has a long history of mining and it looks as though South Crofty Mine will be reopened. This geothermal project has a long history and we lived for many years just a stones throw from Rosmanowes Quarry where a lot of geothermal exploration took place. The Cornish are well used to having their land dug up and I cannot see any self-respecting Cornish person laying down in front of the bulldozers now working at the site.

    • mikewaite permalink
      November 9, 2018 5:57 pm

      Much is made of this project being an example of a renewable technology.
      In order for that to be true, and with what Dave has said in mind, then in one model of the process to maintain water temperature the fission process in the rocks adjacent to the water channel would have to be at the appropriate rate at which the heat is extracted. Does this mean that the rate in the rocks being bathed with the incoming water is similar to that in a small commercial nuclear power station?
      But that would mean that before the deliberate water influx began the rock reservoir would have been experiencing gradually increasing temperatures, to the point presumably that the rock melted -given the age of the deposit.
      Something here does not make sense.
      I presume that the fission rate in the rock reservoir was measured prior to any engineering design work being done. Is that correct?

      • glenwaytown permalink
        November 9, 2018 8:01 pm

        My guess is that the host rock will cool quite quickly and the project will run out of steam – literally!

      • dave permalink
        November 9, 2018 8:55 pm

        The fission process in the rocks is not the source of the heat that is to be harvested – except in the very general sense that this process acting over billions of years is partly responsible for the fact that the interior of the earth is hot.

        I know the blurb makes it sound as if there is a little nuclear reactor down there which is coming on-stream for us. But anywhere in the world, if you drill down a few miles you find the rocks to be two or three hundred degrees C.
        The deep gold mines in South Africa have already reached a level where people can hardly work despite all attempts at cooling the tunnels.

        Judging by this quote,

        “The radioactive decay is the reason the granite is heat producing.”

        the geniuses of Cornish County Council actually believe that tapping a special hot-spot nuclear reactor is exactly what they are giving approval for. What hope is there for the country, when all decision-makers instantly get the wrong end of every stick?

        The actual PRODUCTION of heat in that granite rock is about 1 watt for every 100,000 cubic meters. Or to convert to another point of view ten cubic kilometers of rock is equivalent to a one-bar electric fire.

  11. November 9, 2018 4:55 pm

    What is the visual impact?
    What is the visual impact?

    You might get double vision 😉

  12. It doesn't add up... permalink
    November 9, 2018 8:00 pm

    They’ve already started drilling

  13. Philip Mulholland permalink
    November 10, 2018 9:18 am

    A geothermal power plant that relies on water recycling to operate?
    Two points come to mind;-
    1. This is an extractive industrial process, in which ancient heat is being mined from the granite. As such it cannot be considered as a renewable energy source as it is fossil heat that is being won.
    2. The process of water cycling through hot rocks is equivalent to the natural process of a hydrothermal spring. As such the mineral content of the water being return to the surface will rise. While this may actually be an economic benefit, if the dissolved minerals are valuable, there is still the problem of waste disposal if they are not. Returning mineral charged waste water to the cold rocks of the subsurface is not a good idea as cementation and closure of the injected fractures will damage the fissure permeable properties of the granite at the site of injection. In short the dissolved waste minerals will clog up the fractures in the shallower and colder granite.

  14. andrew jm permalink
    November 12, 2018 2:37 pm

    What is fossil heat?

    • Philip Mulholland permalink
      November 14, 2018 10:47 pm

      Heat that will not be replaced at a sustainable rate of extraction.

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