Shale Gas and Oil Weald and East Kent Report Oct 2014
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CPRE KENT BRIEFING NOTE: SHALE GAS AND OIL EXPLORATION AND DEVELOPMENT IN THE WEALD AND EAST KENT: WATER RESOURCE IMPLICATIONS. 1. EXECUTIVE SUMMARY. This preliminary assessment of the likely water resource impact of hydraulic fracturing has been made on the basis of an interpretation of the local hydrogeology and structural geology described for seven sites; and some general conclusions are drawn with respect to the implications for unconventional hydrocarbon extraction in the Kent and Sussex Weald. Each site has its own distinguishing characteristics but there are a few key features, common to all, which mark them out as potentially vulnerable to seismic disturbance. Consideration is given to what this could mean for the region’s water supplies and the quality of the wider river and wetland environments. The geology varies between sites in terms of age and rock type but they all reveal a history of extensive faulting – evidence of structural weakness. And the high pressures generated by the fracking process could re-activate the faults and initiate a new phase of seismic disturbance, disrupting the rock formations and creating new pathways for the dispersion of toxic gases and fracking fluids. The exploratory sites also feature water-bearing rocks (aquifers) throughout the stratigraphic sequence. Some of these are at relatively shallow depths and support abstraction for local public supplies and agriculture including irrigation. They are also natural reservoirs for springs and seepages feeding the headwater ‘baseflows’ of many of the region’s rivers and wetlands. The relatively close proximity of aquifers to the target shales presents a high risk of contamination from fracking operations. The East Kent exploratory sites can be taken as an extreme case with the Chalk of the North Downs, a major public supply resource, underlain at no great depth (500 – 800m) by the Coal Measures with inter-bedded shales as potential gas/oil sources. The sequence also features extensive faulting with a recent history of seismic disturbance. Contamination can also result from failures in the construction of the exploratory and production boreholes. Casings and grout seals break-down by corrosion and fragmentation, and all boreholes eventually leak. Any assessment of the Wealden sites must also take into account the findings of the British Geological Survey of May 2014 which concluded that there were no opportunities for the extraction of commercially valuable quantities of shale gas. Areas of oil-bearing shales were 2 identified in the west of the region but these are high emission fossil fuels of which UK already has more than sufficient reserves given our commitment to compliance with the 2050 global warming targets. All site appraisals will need to take into account the high levels of water demand associated with the development and production stages, bearing in mind the Environment Agency assessment of all water company supply areas in the South East as “seriously stressed”. Kent is subject to frequent summer hose bans and the supply/demand deficit is forecast to increase under the impact of population growth, climate change and losses in public supply capacity in line with E.C. directives defining environmental sustainability targets. This could leave the water companies with insufficient capacity to meet the additional summer peaks arising from fracking operations without breaching statutory river flow conditions or over drawing on groundwater storage. Hydrocarbon recovery by hydraulic fracturing is a high- risk undertaking, with implications for environmental quality and public health; and the processes involved are, for the most part, carried out at depth and out of sight. Effective regulation therefore requires, as a minimum, continuous 24 hour monitoring and control of all operations, both surface and down-hole, by independent specialist inspectors. We are not however persuaded that the statutory regulators have the necessary staffing levels and resources to ensure compliance by the operators. Remediation of contaminated groundwater can be a lengthy and expensive operation; and major events must often be accepted as, for all practical purposes, permanent and irreversible. In consideration of the over-riding need to protect unique and increasingly vulnerable water resources, we are of the view that there should be a general presumption against unconventional oil and gas development throughout the Weald and East Kent Downland. 2. GENERAL. CPRE Protect Kent is the Kent Branch of the Campaign to Protect Rural England, part of the national CPRE charity. It is our objective to retain and promote a beautiful and thriving countryside that is valued by everyone and we believe the planning system should protect and enhance the countryside in the public interest for the important contribution it makes to peoples’ physical and mental wellbeing, as well as its vital role in feeding the nation. It is our position that local planning authorities should seek to ensure that the impact of development on the countryside, both directly and indirectly, is kept to a minimum and that development is sustainable in accordance with national planning policy. This briefing paper has been prepared as a commentary on the current national interest in shale gas and oil reserves, but focuses on the local hydrogeology of the Weald and East Kent. The following comments and observations are based on the findings from preliminary desk studies relating to sites identified as having potential as sources of commercial quantities of shale gas or oil. The region is known to be underlain at depth by beds of shale, some of which could prove productive, but to extract the methane or oil entails hydraulic fracturing (fracking) to break up the formation using high pressure injection via deep boreholes with lateral extensions of large volumes of water and sand, together with a mix of chemicals, some of 3 which are known to be toxic and/or corrosive1. This gives cause for concern, bearing in mind that the process is designed to break up the shale formations and must therefore be presumed capable of doing the same to other rocks in the immediate vicinity, thereby creating new pathways for the flow of gases and fracking fluids into the overlying shallow aquifers, soils and surface water courses2. The aquifers in question are: The Chalk of the N & S Downs The Lower Greensand (“Ragstone Ridge”) The Hastings Beds of the High Weald and Ashdown Forest. The findings from the recent British Geological Survey (BGS) report of the Jurassic Shales of the Weald Basin, released on 23 May 2014, have been taken into account in the conclusions from our preliminary site assessments. In essence, none of the sites can be regarded as potential sources of commercial quantities of methane gas. There could be shale oil resources but estimates of winnable reserves must await further exploratory drilling. No surveys have as yet been undertaken for the E Kent area. 3. GEOLOGY. 3.1. Figure 1 is a sketch map of the geology of the region, centred on the Wealden Basin, an eroded anticline taking the form of an elongated dome with its W–E axis running from Farnham and Petersfield to the Channel coast at Dover. Figure 2 is a N–S section across the centre of the dome showing the general structure and relationship between the gas-bearing shales and younger formations which include the major aquifers of the region. The oldest exposed formations are the Purbeck beds of the Upper Jurassic and the clays and sandstones of the Hastings Beds which form the core of the anticline. These are succeeded by the Weald Clay – a horse-shoe shaped lowland area flanking the dome to the NE and SW and this is in turn bordered by the Lower Greensand ridge, Gault Clay and the Chalk escarpments of the North and South Downs. The generalised vertical section in Figure 3 shows the two principal shale oil formations; the Kimmeridge Clay and the Lias, at depths of between 1000 and 2000m below ground level (bgl). The sequence is broadly representative of the succession likely to be encountered in the west of the region at Fernhurst and Kirdford or the village sites south of Guildford. Boreholes at these locations would be expected to penetrate more than 300m of Weald Clay and approximately 500m of sandstones, shales, clays and limestones making up the Hastings Beds and Portland/Purbeck succession. These are underlain by 500m of Kimmeridge Clay, an Upper Jurassic formation comprising shales, mudstones and limestones; and this could mark the highest productive level for fracking operations. The developers will however be anxious to prove the potential of a second, lower sequence of around 300 – 400m of shales with subordinate limestones (the ‘Blue Lias’ of the Dorset coast). A parliamentary briefing note 1 Chartered Institute of Environmental Health. Briefing Note. Jan 2013. Hydraulic Fracturing: Impacts on the Environment and Human Health. 2 Chartered Institution of Water and Environment Management. Dec 2013. Hydraulic Fracturing of Shale in the UK. (Policy Statement) 4 “Shale Gas and Fracking”3 identified both the Kimmeridge and Lias as potential methane sources, but these should now be reviewed in the light of the BGS findings. 3.2. Figure 4 can be taken as representative of the N Downs of E Kent, with 250 – 300m of Chalk underlain by 40 – 50m of Gault Clay and a relatively thin Wealden /Jurassic sequence of sandstones, clays, limestones and shales. The Kimmeridge and Lias are not represented in E Kent; and in the Dover area the entire Jurassic sequence is reduced to less than 100m, resting on the Coal Measures of the E. Kent Coalfield, the lower Shale Group of which is likely to be targeted for methane extraction. 4. GEOLOGICAL FAULTS. 4.1. The region features numerous geological faults, evidence of earth movements taking place over the last 150 million years or so.