Earth scientist, Dr Chris Hartnady, has called on stakeholders to not only be aware of the environmental impacts and geophysical risks of shale gas production, but also to evaluate the full energy cost and other economic considerations.

Scientist warns of environmental, geophysical and economic risks

Shale gas is natural gas contained in a shale formation and has become an increasingly important source of natural gas in the United States (US) over the past decade – spreading interest to potential gas shalesites in the rest of the world. One analyst expects shale gas to supply as much as half the natural gas used in North America by 2020. Induced hydraulic fracturing or hydro fracking, commonly known as fracking, is a technique used to release petroleum, natural gas (including shale gas, tight gas and coal seam gas) or other substances for extraction. This type of fracturing creates fractures from a wellbore drilled into reservoir rock formations and has been found to have a serious effect on the quality of water.

Speaking at the Shale Southern Africa Conference in Cape Town earlier this year, Hartnady highlighted factors such as fracking, cement failure, the depletion of water resources and geophysical risks in relation to shale gas production. Important statements that Hartnady made during his presentation are outlined below.

Water resource competition and depletion:

• Hartnady quoted estimates that the exploration phase in three areas of the Karoo would require 48 000 to 216 000 m³ of water from 24 wells. Should exploration be successful, however, actual gas production was likely to require about 10 000 wells; the Marcellus and Barnett shale gas areas in the US (with similar resource assessments) required 12 000 and 14 000 wells, respectively.
• The production phase in the Karoo would require an additional 5 000 to 20 000 m³/well and the water demand would lie in the range of 50 million to 200 million cubic metres. Shale gas production would become a serious competitor for water, requiring as much as four times the current annual usage of the groundwater in all three of the Shell exploration areas.

Groundwater contamination:

• Groundwater contamination was possible due to fracking fluids injected into rocks during the fracking process, cross-contamination of aquifers through drilling-induced fractures crossing groundwater flow paths and casing flaws or failure in well construction.
• Peer-reviewed research into contamination of groundwater at the Marcellus shale gas field in the US showed that thermogenic (from a deep source) methane abundance was 17 times greater within a1 km distance from gas extraction areas, than methane of near-surface biogenic origin in non-extraction areas.

Well casing and cement failure:

• The BP Macondo well blow-out in the deep-water Gulf of Mexico was caused by loss of control over the gas influx into the well, through faulty casing and the cement seal.
• Cement has little tensile strength of its own and fails in tension before lending significant support to the casing. The Achilles heel is the casing shoe. The assumption of no contact between the cement sheath and borehole is unrealistic. Gas can easily escape up the casing or outside the casing in the fractured zone.

Geophysical risks:

• Referring to the 5.6 magnitude Oklahoma earthquake in 2011, Hartnady (internationally renowned for his expertise in structural geology and tectonics) said this state had previously experienced around 30 small earthquakes a year. Since 2010/2011, this had soared to over 1 000 a year.

Hartnady attributed this dramatic increase to the accelerated disposal of wastewater brines from unconventional oil and shale-gas production, often in refurbished old oil wells in depleted areas of former conventional oil production areas. “The 2011 ‘hydroseismic’ events in Oklahoma and Ohio bear important lessons for the Karoo, especially since – though not common knowledge – significant earthquake activity is established in this part of the country. The earthquake catalogue of South Africa shows many epicentres within and around the Karoo.”

Economics of shale gas drilling:

• A focus only on environmental impacts and geophysical risks, without questioning the economics of shale gas drilling, was counterproductive, said Dr Hartnady.
• Energy cost considerations (energy required for extraction, processing and distribution) indicated a low net energy yield of shale gas development. The ratio of energy profit to energy investment was likely to be much lower than conventional fossil fuels, perhaps around factor 10at best and possibly near break-even at worst.
• Much depended on what energy costs were internally accommodated by the commercial producers and what was externalised through hidden or overt energy subsidies paid for by government and tax payers.

“The most important part of energy security is ensuring that there is indeed a reasonable and profitable energy return on the energy investment (capital equipment, labour, transport infrastructure and all necessary public services), when all energy costs are summed.”

There is a need for prior scientific investigations of the deep (probably saline) aquifers within and underlying the main Karoo basin, and concurrently the crustal stress regime within and around those units, as well as a full lifecycle analysis of both energy and water consumption within the shale gas production process.

He proposed that the Karoo shale gas initiative, which is based on a finite, non-renewable resource unlikely to last till the end of the 21st century, be measured up quantitatively in a direct and competitive challenge against “the ultimate energy-value proposition in this part of the world. The Karoo shale gas concession is an area of excellent direct normal irradiance, which constitutes one of the very best opportunities on the planet – as good if not better in some respects than parts of the Sahara – for concentrating solar power generation. So why look down to shale gas as a profitable energy operation, [when] instead we should all be looking up.”