In the second of our two-part special on fracking, Margaret Franklin explains the processes involved in hydraulic fracturing and addresses the environmental concerns surrounding fracking operations
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Author: Margaret Franklin, MSc, FICI, vice president, Institute of Chemistry of Ireland

Natural gas is a non-renewable fossil fuel, formed in a marine environment millions of years ago. It arose from the anaerobic decomposition of the remains of tiny marine organisms that died, sank to the sea floor and became trapped in sediments. Over millions of years, the sediments were compressed into sedimentary rocks, such as shale or sandstone.

Natural gas is composed mainly of methane (CH4), the least dense hydrocarbon. There may sometimes be traces of other hydrocarbons present, as well as contaminants such as hydrogen sulphide (H2S). If H2S is present, it needs to be removed before the gas is distributed. Methane cannot be liquefied at normal ambient temperatures and so cannot be bottled like propane or butane. It must be distributed by pipeline.

Fracking, Ireland and natural gas


Ireland has significant reserves of natural gas, both off-shore and on-shore. Marathon Oil started oil exploration off the south coast of Ireland in the late 1960s, but found no oil. In 1971, a natural gas field was discovered 50 km off the Old Head of Kinsale, in a water depth of one kilometer below the seabed. It is contained in layers of porous sandstone, formed about 100 million years ago.

The sandstone is overlaid with impermeable layers of shale and chalk. Kinsale gas is exceptionally pure, almost entirely composed of methane, so that no clean-up is necessary. In 1976, the gas was first brought ashore, via an undersea pipeline, at Inch in Co Cork. In the same year, An Bord Gais was established to distribute the gas. A pipeline was laid to bring the gas from Cork to Dublin and other towns along the route.

In 1993, Bord Gais built the first interconnector with Scotland, allowing gas to be imported from the UK. The Malaysian company Petronas acquired the Kinsale gas facility in 2009. It also operates the associated Ballycotton and Seven Heads gas fields, as well as Ireland’s only natural-gas storage facility. During the summer months, when gas demand is low, gas is injected into an underground offshore cavern, which acts as a reservoir. In winter, when demand rises, the gas is pumped out. The reservoir has a capacity of 230 million cubic metres (one cubic metre of gas is equivalent to about 10 kW-hrs of energy).

In 1996, Shell discovered the Corrib Gas field off the West coast. This gas contains hydrogen sulphide, which Shell proposes to remove at its on-shore terminal at Bellanaboy Bridge, Co Mayo. There was strong local opposition to the project, resulting in major delays. In 2002, the pipeline from Dublin to the West was completed and a second interconnector to Scotland was laid.

The Kinsale Gas Field and its satellite fields now provide only 15% of Ireland’s natural gas needs and this is expected to decline as the gas becomes exhausted. We are dependent on imported gas to supply the remaining 85% of our needs.

According to Shell, Corrib Gas is capable of supplying up to 60% of Ireland’s needs for up to 20 years. Ireland now has a good natural gas infrastructure, in terms of a distribution network, the two interconnectors and a gas storage facility. To ensure security of energy supply, it is important that our on-shore natural gas reserves be developed.

Unconventional gas fields and fracking


Both the Kinsale and the Corrib gas fields are what are known as ‘conventional’ gas fields. It is relatively easy to release natural gas from such fields by vertical drilling. However, much of the world’s natural gas is contained in ‘unconventional’ reservoirs, where the gas is trapped in highly compacted rock, such as shale or ‘tight’ sandstone.

New techniques, involving horizontal drilling, combined with so-called ‘fracking’ are needed to release the gas from these reservoirs. Ireland has significant on-shore reserves of natural gas in unconventional fields. In the past, it was deemed uneconomical to extract it and moreover, fracking has been controversial in the United States. However, with rising energy prices and the need for a secure energy supply, it may now be time to consider the feasibility of developing Ireland’s on-shore gas.

Fig 1: The fracking process (click to enlarge)

Fracking is the colloquial term for the process of ‘hydraulic fracturing’, which is used extensively in the US to extract natural gas from unconventional fields. It involves pumping fluid into a deep borehole at very high pressure, causing the rock to fracture, in order to facilitate the release of the gas (Fig. 1). A vertical borehole is sunk to the required depth and drilling is then continued in a horizontal direction, before the fracking fluid is pumped in. Geologists and engineers can now drill into thin seams of gas or oil-rich shale, in a process known as ‘high angle geosteering’.

The ability to precisely navigate the drilling depends on sound understanding of sub-surface geology. Geological interpretation continues while drilling, to place the well bore where there is the highest concentration of hydrocarbons. The fracking follows the drilling and may involve in the region of 400,000 gallons of water and 500,000 lbs. of sand. Pump rates of 2,000 gals per minute produce surface pressures of >5,000 psi, so it is an energy-intensive process.

The fluids used in fracking consist mainly of water, along with sand and chemical additives. The sand serves to prop open the fractures, thus facilitating the release of the gas. The chemicals include acid to help dissolve minerals in the rock, disinfectants to prevent bacterial growth, corrosion inhibitors to protect the pipe and materials to reduce friction and improve viscosity.

Typical additives used in fracking fluids are shown in Table 1. All of these chemicals are already in common use for other purposes and at the concentrations used, pose no danger to the environment.

TABLE 1: TYPICAL ADDITIVES USED IN FRACKING FLUIDS

Additive Type Compounds Purpose Common Uses
Diluted Acid HCl Dissolve minerals Numerous
Biocide Gluteraldehyde Kills bacteria Disinfectant
Breaker Ammonium persulphate Delay breakdown of gel Bleach (hair products & detergents)
Corrosion inhibitor Dimethyl formamide Prevents pipe corrosion Pharmaceuticals & plastics
Crosslinker Borate Salts Maintains viscosity Soaps & detergents
Friction reducer Polyacrylamide & oil Reduces friction between pipe & fluid Water treatment, Make-up remover
Gel Guar gum, or hydroxyethyl cellulose Thickens fluid to suspend the sand Toothpaste, sauces, icecream
Iron Control Citric Acid Prevents precipitation Food flavouring
KCl Potassium Chloride Brine carrier fluid Fertilizer, sodium substitute
Oxygen scavenger Ammonium bisulphate Prevents corrosion Food, cosmetics.
pH control Sodium carbonate Helps crosslinkers Soap, glass & ceramics
Proppant Silica, quartz sand Props open fractures to allow gas escape Sand filtration, concrete
Scale inhibitor Ethylene glycol Prevents scale in pipe Antifreeze, cleanser.

FRACKING IN IRELAND

Fracking has not yet been used on a commercial basis to extract natural gas in Ireland. It has been established that there is natural gas in the Lough Allen and Clare basins. The Lough Allen basin is a huge area of 8,000 square kilometres, extending through parts of North Mayo, Sligo, North Roscommon, Leitrim, Donegal, Monaghan, as well as over the border in Fermanagh and Tyrone. The Clare basin includes parts of counties Clare, Limerick, Kerry and Cork.

Exploration in these areas started in the 1960s and a number of wells have been drilled over the years. Every well yielded gas but, at the time, extraction was uneconomical. In 2011, licences were granted to three companies to carry out exploration for natural gas in the Lough Allen and Clare basins. Some shallow exploratory drilling has taken place. These licences have now expired. There is considerable local opposition to fracking, as environmental groups have raised various concerns.

The main concerns and questions posed by fracking operations are:

  • Chemicals from fracking fluids may contaminate ground and surface water;
  • Materials brought up from the underground sediments may cause water and soil contamination;
  • There is risk of release of volatile organic compounds to the atmosphere;
  • Radioactive substances may be brought to the surface;
  • Management and disposal of wastewater is a cause for concern;
  • There are questions about the environmental impacts of the well injection and the fracking process itself;
  • There is a risk of induced seismicity (small, artificially-produced earthquakes);
  • The effect of abstraction of large quantities of water from aquifers requires consideration.

Addressing the concerns


Regarding water contamination from the fracking operations, it should be noted that the water table is typically at a much higher level than the gas-bearing strata, with a layer of impermeable rock in between the aquifer and the gas. The borehole casing is of critical importance. It should be so constructed as to prevent the fracking fluids from leaking into the aquifer, as the liquid is being pumped underground. Any fracking fluid that seeps from the fracked rocks cannot contaminate the groundwater, as the former is at a much lower level than the latter. In any case, the chemicals used in most fracking fluids pose no threat to the environment at the levels used.

Fig 2: Potential water contamination from fracking (click to enlarge)

Of greater concern is the possibility of contamination from the shale itself. Substances present in the shale may dissolve in the fracking fluids and may be brought to the surface during flow back. Apart from methane (the natural gas itself) they may include carbon dioxide, hydrogen sulfide, nitrogen, helium, trace metals (e.g. mercury, arsenic and lead) radioactive elements (e.g. radium, thorium and uranium) and volatile organic compounds such as benzene. Careful monitoring of fracking fluids and flowback fluids is required to mitigate the risks from this potential source of contamination.

One way of dealing with the liquid waste is by ponding and evaporation on site. Evaporation concentrates the contaminants and this increases the risk of environmental damage if a leak occurs. Tailings ponds must comply with the same standards as any mining operation. An alternative is to transport the waste away from the site, but there is risk of spillage during transportation and the waste still needs to be dealt with elsewhere.

Some operators in the US re-use the flowback fluid for further fracking operations at the same wellhead, but the cost of removing contaminants from previous cycles make this unattractive. Flowback fluid is classified as mine waste in the EU and is governed by the Mining Waste Directive.

Release of radioactive materials and volatile compounds to the atmosphere is also a cause for concern. Leakage of methane could have a high greenhouse gas footprint. However, conventional gas extraction also carries this risk and it is not clear if the risk is any greater when fracking is used. The release of radioactivity, especially that due to Radium 226, is a potential hazard. Fracking operations need to minimise all emissions to the atmosphere and monitoring processes need to be enforced.

The use of liquefied propane is an alternative to the use of water as the main carrier fluid in fracking. GasFrac Energy Services, in Alberta, Canada, has pioneered this system. Propane gel is injected under high pressure into the shale or sandstone. It gasifies during the process and is recovered, re-used or sold. The process uses no water and therefore produces no wastewater. This is an emerging technology, which needs to be tried and tested, but it is worthy of consideration.

It is possible that fracking may cause minor earthquakes, but the tremors rarely register more than 3 or 4 on the Richter scale and would normally not be noticed above ground. This induced seismicity is usually related to pre-existing faults in the rock. Fracking acts as a trigger to release energy already stored in the fault. It is important that geological surveys are performed, so that fracking is avoided in the vicinity of such faults.

Environmental studies and EU Directives


In May 2012, the Environmental Protection Agency (EPA) published a report on a preliminary study conducted by the University of Aberdeen (1). The main findings are set out under three headings:

  • Potential Environmental Impacts;
  • Regulatory Approaches used in other countries; and
  •  Established best practice.

This report is worthy of study and can be downloaded from the EPA website (2). A further report is pending and Minister Pat Rabbitte has said that no further licences will be granted unless the EPA report is favourable.

We are bound by a number of EU Directives, which are listed below (3). Within the limits set by these directives, each country is free to make its own decisions in regard to fracking. Policy differs greatly from one country to another and seems to be largely dictated by political considerations. Poland has large reserves of shale gas and is embarking on an extensive drilling programme. Germany also has shale gas and drilling is underway. Bulgaria granted exploration licences to Chevron, but then outlawed fracking in 2012.

The UK is in favour of it, but suspended fracking after two small earthquakes occurred near Blackpool in 2011. France banned fracking in 2011 due to pressure from environmental groups. The EU has set up a working group on the regulation of shale gas extraction.

The use of hydraulic fracturing to extract natural gas is not without its hazards. Mistakes have been made in the past, but the technology is in use in a number of countries. With adequate geological surveys, sound well casings, proper waste management and environmental protection measures, it can be done safely and with minimal damage to the environment. Many of the concerns raised by environmental activists are based on ill-informed scaremongering.

However, it is important to consult those who are likely to be affected by fracking operations in the vicinity of their homes and their concerns need to be addressed. Planning decisions should be made on the basis of sound scientific advice and engineering knowledge, rather than on irrational fears and political lobbying.

It is possible to develop Ireland’s natural gas while protecting the environment. In the interests of maintaining a secure energy supply into the future, it is imperative to do so.

This article is based on Margaret Franklin’s presentation at a meeting hosted by Engineers Ireland Midland Region at AIT Athlone on 28 April 2014. Click here for the first article in this series.

References

(1) Hydraulic Fracturing or ‘Fracking’: A Short Summary of Current Knowledge and Potential Environmental Impacts. Author: Dr Dave Healy

(2) www.epa.ie/pubs/reports/research/sss/epa-strivesmallscalestudyreport.html#.U2fEyMflf1w

(3) Drinking Water Directive (1998), Water Framework Directive (2000), Groundwater Framework Directive (2006), Mining Waste Directive (2006), Noise Directive (2002), Biodiversity: Habitats Directive(1992)

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  Author: Margaret Franklin, MSc, FICI, vice president, Institute of Chemistry of Ireland Natural gas is a non-renewable fossil fuel, formed in a marine environment millions of years ago. It arose from the anaerobic decomposition of the remains of tiny marine organisms that died, sank to the sea floor and became...