Shale gas

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Schematic representation of oil and gas production from conventional and unconventional deposits. On the far right the shale gas deposit in the “shale”.

Shale gas ( English shale gas ) is in shales contained natural gas . Shale gas is considered "unconventional" natural gas in contrast to "conventional" natural gas, which comes from deposits in coarse-grained rocks and has accumulated in so-called natural gas traps .

etymology

The term shale gas originates from the traditional use of the term shale for any kind of easily fissile rock. This also included unfolded clay stones from which shale gas is extracted today.

In geological terminology, slate is now only used for folded clay stones ( clay slate ) or certain metamorphic rocks ( crystalline slate ). These folded or metamorphic rocks no longer contain gas or have never contained any. Nevertheless, the term shale gas - in contrast to shale oil - has also established itself among raw material geologists.

Another reason is the imprecise translation of the English term shale gas : shale is synonymous with a thin-plate ("schistige") unfolded claystone, while slate in the real sense is translated either as slate (clay slate) or schist (crystalline slate).

Emergence

The creation of shale gas corresponds to the first steps in the creation of conventional natural gas. Natural gas initially forms (matures) in a claystone rich in organic matter, the so-called host rock. To become conventional natural gas, it must emerge from the bedrock and then wander in the pore space relatively permeable (permeable) rocks into a reservoir (gas trap) ( migrate ). However, if the bedrock horizon is sealed up and down by impermeable rock, the gas cannot escape and remains in the bedrock. This gas, which is still in the bedrock today, is called shale gas .

Carbon isotopes and anthropogenic methane emissions

Compared to the natural gas of conventional deposits, shale gas has lower ('lighter') δ 13 C values, i.e. it is enriched with the lighter carbon isotope 12 C. This is explained by the fact that conventional natural gas partially absorbs during migration and in the deposit is subject to biogenic (bacteria) or thermal oxidation processes, in which preferably the lighter 12 C is involved.

This enables conclusions to be drawn about the contribution of shale gas production to global methane emissions. Since the δ 13 C value of atmospheric methane has decreased since the mid-2000s while methane emissions have increased, it was assumed that this increase was mainly caused by recent biogenic methane (tropical wetlands, rice cultivation, livestock farming). Instead, the decrease in the δ 13 C value could be largely due to methane emissions from shale gas extraction (cf.Greenhouse gas immission through hydraulic fracturing ), which suggests that shale gas extraction makes a significant contribution to the overall input of the very effective greenhouse gas methane into the earth's atmosphere suggested.

Properties and occurrence of gas-bearing mudstone formations

World map with gas-bearing mudstone formations

Mudstone formations that contain economically recoverable amounts of gas have some common properties. These are mostly geologically older ( Paleozoic or even Proterozoic ) marine sedimentary rocks that are rich in organic material (0.5 to 25%). Layers suitable for shale gas production must be brittle enough so that naturally occurring or artificially created cracks do not close up again under the lithostatic pressure in the depth. Sometimes relatively strong natural gamma radiation (clay stones in question are called hot shales ) with a high carbon content. Such claystone layers are considered to be particularly productive. However, the amount of gas stored in clay stones per unit volume of host rock is generally lower than in conventional deposits.

The gas is partly in natural cracks or disperse distribution in the non-interconnected pores of the rock, sometimes it's clay particles adsorbed . When pumping by hydraulic fracturing, the non-adsorbed gas is released immediately, while the adsorbed gas is only desorbed with a delay due to the pressure drop that the rock experiences through drilling and fracturing.

Gas-bearing claystones can be found - similar to conventional natural gas reservoirs - everywhere in the world where the cratons or younger fold belts are covered by largely unfolded platform sediments. These regions include the continental platform of North America ( interior platform ), the Eastern European platform , the Paris Basin , the North German-Polish Basin and the Karoo Basin . Commercial shale gas production has so far (as of 2015) only been operated in a few of these regions. The countries with the largest technically recoverable reserves in western Europe are France and Poland, each with an estimated 4 trillion cubic meters.

United States

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US Shale
Gas Production by Formation (Billion Cubic Feet / Day)

One of the largest known occurrences in the United States is in the Marcellus Formation . It consists mainly of black slate and subordinate light shale and limestone from the Middle Devonian and extends over an area of ​​almost 250,000 square kilometers on the eastern edge of the North American platform.

In 2014, the EIA, the US national energy statistics agency, forecast total production from the seven most important shale gas-bearing formations of 10.6 trillion cubic meters (377 trillion cubic feet) with a daily production from these formations of 1.18 billion cubic meters ( 41.8 billion cubic feet) in the year 2040. Critics of the carbon-based energy industry, however, viewed these figures as far too optimistic, and even considered it possible that, for geological and economic reasons, the maximum production in the "top seven" will be reached by 2017 at the latest would.

After a price decline in 2014 and 2015, the natural gas price on the national gas market has stabilized at a low level from mid-2016 at around 3 US dollars per MMBTU (26.4 m³). This is why the US shale gas producers have problems operating profitably. Sun declined from June 2013 to June 2019, the value share of oil and gas stocks in the US stock index S & P 500 by 4.6% to 8.7%, and approximately 175 companies had from June 2015 to June 2019 for bankruptcy protection apply. Nonetheless, the EIA estimates that the average daily production of shale gas increased from 43.5 to 68.5 billion cubic feet, or 57%, from June 2015 to June 2019.

According to an estimate by the US energy statistics agency from 2013, China is the country with the largest shale gas reserves in the world

China

According to various estimates, China has at least 20 trillion cubic meters of technically recoverable shale gas reserves. Deposits are located in almost all parts of the country, especially in the Tarim Basin and Junggar Basin in the northwest, the Songliao Basin in the northeast and the Sichuan Basin in the south. The gas-bearing claystone formations originate predominantly from marine deposits and are mostly Paleozoic in age. Because China's sedimentary basins have relatively complicated tectonics due to their complex geological history , shale gas extraction there is technically much more demanding than in large parts of the USA. The Sichuan Basin is considered to be particularly suitable geologically. The first successful tests for commercial shale gas production were carried out there, with the first fractured vertical well in 2009 (well "Wei-201", with production rates of 150,000 m³ / day in 2010) and the first fractured horizontal well in 2011 ( Hole "Wei-201-H1"). In 2013, shale gas production in China was 200 million cubic meters, which although not even 0.2% of total natural gas production in the country, was an increase of almost 600% compared to the previous year (30 million cubic meters).

Germany

Areas with shale gas potential in Germany (in orange)

According to estimates by the Federal Institute for Geosciences and Natural Resources , the total deposits of shale gas ("gas in place") amount to at least 7 trillion cubic meters (maximum 23 trillion), of which at least about 10% (maximum 35%) can be technically extracted using fracking, that is, the shale gas resources amount to at least 700 billion cubic meters (corresponds to about 7 times the annual consumption of the FRG in 2010). This more than doubles conventional natural gas resources (150 billion cubic meters) and economic reserves (146 billion cubic meters). Numerous geological horizons are possible for shale gas extraction, in particular alum shale and rocks from the Kulm and coal limestone facies of the North German Lower Carboniferous (depth 1050 to 5000 meters), the Posidonia slate of the North and South German Lower Jurassic (depth 1550 to 2150 meters) and claystones rich in organic compounds the North German Lower Cretaceous (" Wealden ", depth 1300 to 1660 meters).

Extraction

Scheme of a production well

Shale gas is mainly obtained through hydraulic fracturing ( fracking for short , hydraulic cracking).

Mudstone has low permeability and commercial-scale shale gas extraction requires cracks to provide this permeability. Shale gas has long been extracted from formations with many natural cracks.

By directional drilling horizontal wells which increase the exit surface for the stored gas in the shale arise. A liquid ("Fracfluid": water, sand and chemicals) injected under high pressure creates a gas-permeable structure around the drill string. There are massive environmental concerns about fracking .

Web links

Commons : Shale Gas  - Collection of Pictures, Videos and Audio Files
Wiktionary: shale gas  - explanations of meanings, word origins, synonyms, translations
  • Angelika Hillmer: Frac technique. Pumping gas at high pressure. Hamburger Abendblatt, December 14, 2010, accessed on February 11, 2013 .
  • Sven Titz: Shale gas - the rediscovered reserve. New technologies enable the profitable extraction of unconventional gas deposits. Neue Zürcher Zeitung, January 6, 2010, accessed on February 11, 2013 .
  • Markus Theurer: In search of shale gas. Frankfurter Allgemeine Zeitung, March 15, 2010, accessed on February 11, 2013 .
  • Werner Zittel: Unconventional natural gas. (PDF) Short study. ASPO Germany / Energy Watch Group , May 18, 2010, archived from the original on July 9, 2015 ; Retrieved February 11, 2013 (information paper).
  • Andrzej Rybak: Drilling to the center of the earth. In: Agenda. Financial Times Deutschland, September 4, 2009, archived from the original on September 6, 2010 ; accessed on February 11, 2013 : "Poland dreams of a new treasure: shale gas"

Individual evidence

  1. ↑ a b Robert W. Howarth: Ideas and perspectives: is shale gas a major driver of recent increase in global atmospheric methane? Biogeosciences. Volume 16, 2019, pp. 3033-3046, doi: 10.5194 / bg-16-3033-2019 .
  2. ^ Ground Water Protection Council, ALL Consulting: Modern shale gas development in the United States: a Primer. US Department of Energy, Office of Fossil Energy / National Energy Technology Laboratory, Washington, DC / Morgantown, WV 2009 (online) , p. 17.
  3. ↑ US Energy Information Administration (EIA): Technically Recoverable Shale Oil and Shale Gas Resources: An Assessment of 137 Shale Formations in 41 Countries Outside the United States. US Department of Energy, Washington, DC 2013 ( PDF 65 MB), p. 6.
  4. ^ Joel Kirkland: Big Money Drives Up the Betting on the Marcellus Shale. New York Times, July 8, 2010, accessed June 23, 2011.
  5. ^ David Hughes, Drilling Deeper - A Reality Check on US Government Forecasts for a Lasting Tight Oil & Shale Gas Boom. Part 3: Shale gas. Post Carbon Institute, Santa Rosa, CA 2014 ( PDF 14.3 MB), p. 301 f.
  6. ^ Clifford Krauss: US Oil Companies Find Energy Independence Isn't So Profitable. New York Times, June 30, 2019, accessed August 19, 2019.
  7. ↑ Natural Gas Weekly Update for week ending August 14, 2019: Monthly dry shale gas production. EIA website ( raw data as Excel sheet )
  8. ↑ a b Lei Tian, ​​Zhongmin Wang, Alan Krupnick, Xiaoli Liu: Stimulating Shale Gas Development in China - A Comparison with the US Experience. Resources for the Future Discussion Paper 14-18. Resources for the Future, Washington, DC 2014 (online) , p. 3 f.
  9. ↑ a b c Pingli Liu, Yinsheng Feng, Liqiang Zhao, Nianyin Li, Zhifeng Luo: Technical status and challenges of shale gas development in Sichuan Basin, China. Petroleum. Volume 1, No. 1, 2015, pp. 1–7, doi: 10.1016 / j.petlm.2015.03.001 (Open Access).
  10. ↑ Haipeng Li, Jiang Zaixing: Progress and Prospects for Shale Gas Exploration and Development in China. Advanced Materials Research. Vol. 962–965, 2014, pp. 600–603, doi: 10.4028 / www.scientific.net / AMR.962-965.600 (alternative full text access : ResearchGate )
  11. ↑ Tang Limin: Current Situation and Opportunities of Sichuan Shale Gas Exploration and Development. 14th US - China Oil & Gas Industry Forum, 24.-26. September 2014 ( presentation as PDF 13.8 MB)
  12. ↑ Jonathan Watts: China takes step towards tapping shale gas potential with first well. The Guardian, April 21, 2011, accessed September 14, 2014.
  13. ^ Piotr Heller: With high pressure . Natural gas extraction through fracking is a hot topic. Frankfurter Allgemeine Sonntagszeitung, February 24, 2013, issue No. 8, p. 61 .
  14. ↑ Harald Andruleit u. a .: Estimation of the natural gas potential from dense clay rocks (shale gas) in Germany . Ed .: Federal Institute for Geosciences and Raw Materials. ( PDF ).
  15. ↑ Susanne Arndt, David Rotman, Wolfgang Stieler: The brute search for gas in rock. Spiegel.de, October 17, 2010, accessed on February 11, 2013 .
  16. ↑ Dimitrios Kolymbas: Tunnel construction and tunnel mechanics . A systematic introduction with special consideration of mechanical problems. Springer, Berlin 1998, p. 279 .
  17. ↑ Werner Zittel: Great Hope Shale Gas. Total humbug. n-tv.de, May 20, 2010, accessed on February 11, 2013 .