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Shale And Tight Gas: To Frack Or Not To Frack?

A controversial unconventional energy source

Date : 08/10/2014

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Daniel

Uploaded by : Daniel
Uploaded on : 08/10/2014
Subject : Geology

'Chimaera the unconquerable. of divine birth was she and not of men . breathed dread fierceness of blazing fire' wrote Homer ('Iliad') of the mythical Greek monster Chimaera. Euhemerism would indictate the origin of this myth to be the natural eternal flames of Mount Chimaera, above, a site of subtarranean combustion of methane, the primary constituent of natural gas.

Today, pubic anxiety about natural gas is heightened by discussions regarding fracking, especially after the 2010 film 'Gasland' by Josh Fox. Shale and tight gas comprise part of the gas resource base traditionally overlooked in exploration for being considered too difficult or costly to produce: they are 'unconventional'.

Breaking conventionality

Shale gas comprises natural gas trapped in microscopic pores, bubble like pockets of space between the tetris of clay minerals that constitute shales. The amount of pore space in a rock defines its porosity. Shales actually tend to have relatively high porosities and thus store a large amount of gas per unit volume. But importantly they have very low permeabilities; in other words, the degree to which a fluid or gas will flow through a rock is very low and gas can only be removed and produced economically if the permeability is increased.

The difference between shale gas and tight gas is that in the former the gas is trapped in the rock, as opposed to the gas being dispersed within low-porosity silts and sands. In the general case of tight gas then, the individual pores are less likely to be 'in contact' with each other on account of their lower abundance. Therefore permeabilities are lower. However, the permeability-porosity relationship is dependent on a number of rock characters including composition, structures and fabrics.

Inducing flow

The move to harvest unconventional gas resources seems to have shook-up the economic energy landscape almost overnight, prompting The Economist to release a special report earlier this summer (see http://www.economist.com/node/21558432). However, on a scientific level, it has taken many decades of research to reach a level of technical understanding that permits economic production from gas-rich but low permeability reservoirs. The logistics of producing from these reservoirs is also a major challenge given that most have a wide spatial occurrence, whether at the surface or below.

To permit flow between pores in tight gas and shale gas reservoirs, permeability must be artificially induced. Hydraulic fracturing, or fracking, is a proven technology and not an overnight sensation: in the US alone, over 1 million wells drilled since the 1940s have employed fracking as a means of increasing oil and gas yield during a typical well lifetime of 20-40 years. Fracking involves the targeted pumping of high pressure fluid into horizontal and vertical wells to create fracture pathways for gas flow in target formations (see http://www.youtube.com/watch?feature=player_embedded&v=vO82b2auSdo). Software advancements now enable engineers to track and map the fracture network, to better target fracture propagation for increased efficiency in production but also to monitor the evolving fracture network and flow of fluids for safety and environmental purposes.

'Break bread, not shale'

'There are so many myths about this, it's easy to envision something happening badly', said Bob Dudley, CEO of BP in July this year. With France, Belgium and Bulgaria rdeclaring a moratorium on gas extraction by fracking this year, what do environmentalists and some governments believe could go wrong?

Water pollution and pollution due to water:

If ran to the enviornmental standards set by the Ground Water Protection Council (GWPC) and Environmental Protection Agency (EPA), fracking has the potential to and environmentally safe and efficient process. Fracking fluids consist of around 90% water, 9.5% sand/silt mixture and the remaining 0.5% consist of a tonic of various chemicals whose environmental impact is debated. Vast amounts of water are needed for successful fracking - about 5-10 million gallons of water per well per frack job. With these wells being protected by an armored bank-vault worth of steel, an industry standard for wellbore isolation, shielding against aquifer contamination during injection is of the topmost priority.

Post fracking however, bubbles of flammable natural gas become disseminated through the flowback fluids, together with metals, salts and pollutants. What's more, additional water is gained from underground reservoirs. Incidently, this additional flowback may cause groundwater withdrawal from lower level aquifers. To date, all this return water has mostly been disposed of by injection into deep exhausted wells. The scale of transport jobs are enormous: hundreds of truckloads of water, driven by oil and pumping out carbon, whilst wearing down the typically temporary muddy roads cut across the landscape towards the well location. This must change: recycling water on site must be a top priority and an essential standard for production. If the quality and efficiency of the recycling methods can be improved then emissions and the impact on freshwater stocks can be minimised even if neutrality cannot be attained.

Landscape impacts:

Discussions regarding the environmental and socio-economic impacts of shale gas exploration are similar to those for surface mining. The physical infrastructure for shale gas exploration includes: access roads, water reservoirs and supply lines, well pads, gathering lines and compressor stations. Open-pit mining for fracking sands must also occur. The landscape impacts are far-reaching, especially given the typically wide-scale of operation. They include habitat destruction and fragmentation, drainage alteration, and changes to sedimentation patterns. These in turn influence landforms, watershed and viewsheds, habitat quality and biodiversity.

Effective mitigation calls for creative and efficient planning by exploration companies in land management and workflow across the wider shale gas field, including post-development landscape reclamation. Practices must be dictated by strict guideline from national governmental environmental agencies. Comprehensive assessments and regulations for industry procedure during shale gas ventures are already in place in the US, with reforms taking place regularly. Management and enforcement of these acts appears to be somewhat more difficult, whether it be due to a lack of inspections or compliance by oil and gas companies. Certainly, with the number of violations per year doubling in Pennsylvania these past four years, despite a drop in the number of wells drilled and an increase in inspections, it suggests the standards of operator practices are decreasing. It is worrying that despite the state of Pennsylvania's allowance of this debated practice, industry is missing a clear opportunity to improve its environmental records, public image and competitive edge.

Wide scale destruction during shale gas extraction, Wyoming, USA. Effective land reclamation is needed to alleviate the effects on the landscape. (Image: National Geographic)

Wider views

As anyone with a grasp of climate change should be, I'm a proponent of a future energy pathway in which renewables play an increasingly important role. However, while renewable energy is growing rapidly, it is expected to contribute only 6% of global energy supply by 2030. With energy consumption expected to rise by 40% in that time, I feel very strongly on two points. Firstly, tide and solar energy appear to be undervalued relative to wind in the current renewables landscape in the UK and their importance must increase. Secondly, displacing coal with natural gas on a large scale in power generation is a vital change that is needed to combat the acceleration of global climate change. Fuel substitution of coal and oil by natural gas is expected at a rate of 2.4% per annum (p.a.) in the power sector and 2.1% p.a. Realism dictates therefore that reserves of natural gas, whether unconventional or conventional, need to be located and exploited to maximum efficiency. Shale gas seems a primed exploration target to facilitate this shift to natural gas production, with governments likely to preach the advantages to energy security, the economy and carbon output a decreased reliance of foreign energy imports will bring.

Shale or wind? Will shale gas wells, such as this one in Pennsylvania, complement onshore wind turbines in the UK in the future? (Images: Getty)

With regards to renewables, a debate is ensuing in the UK between coalition party secretaries about the importance of renewables and shale gas exploration in future British economy policies. The crux of the debate is that a number of important Tory politicians favour tax breaks on shale gas investment over subsidies on green technologies. George Osbourne, the UK Chancellor, recently indicated that the government are 'consulting on a generous new tax regime for shale'. The new Environmental Secretary Owen Paterson, ironically a known climate change sceptic, has apparently asked for an end to 'all energy subsides and fast-tracked exploitation of shale gas'. Given what I've summarised here, that wouldn't be too wise for the environment. However, gaining short term boosts to the economy in the current double-dip recession seems to be Osbourne's game. His method of doing so in this instant must be to the dismay of Ed Davey, the coalitions Energy and Climate Change Secretary. At the Liberal Democrat party conference last month, he reiterated his view that growth in the green sector should be 'at the heart of rebalancing the British economy'. There could be controversial evolutions in energy policies these next few months so its worth watching this space.

notes:

Comprehensive future outlooks for global energy are provided by BP (http://www.bp.com/sectiongenericarticle800.docategoryId=9037134&contentId=7068677)and Shell (http://www.shell.com/home/content/future_energy/scenarios/)

This resource was uploaded by: Daniel