Grouting

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When pressing or sinking is disposal of waste gases and waste waters designated in underground rocks. The technical process of introducing it into the target formation is also called injection .

purpose

The purpose of the injection is to permanently remove large amounts of problematic substances from the atmosphere and biosphere as cheaply as possible . This includes toxic wastewater that z. B. arise in mining , in the chemical industry or in the production of oil and natural gas . In particular, carbon dioxide (CO 2 ), which is a greenhouse gas and is produced in large quantities when burning fossil fuels , should also be disposed of in this way (see →  CO 2 separation and storage ).

principle

First, a borehole is sunk into the target horizon. The target formations are usually permeable ( porous and / or permeable ) rocks such as sandstone or reef limestone in which the injected fluids can be well distributed. Strongly fractured crystalline can also be used. Carbon dioxide should also be injected into coal seams that can not be mined profitably because it is adsorbed on the coal . The fluids are injected under high pressure (up to several megapascals ), because the target horizon is usually several hundred to several thousand meters deep . The injection pressure must be higher than the pore pressure in the target formation, for which at least the hydrostatic pressure in the corresponding depth must be assumed (gradient ≈ 10 kPa / m).

Practice and problems

While the routine injection of carbon dioxide is still the exception worldwide (one of the flagship projects is the injection of CO 2 underground in the North Sea, which has been ongoing since 1996 and is separated on site from the raw gas from the Sleipner offshore gas field ), wastewater has been used since disposed of in the deep underground for several decades. Volumes of a few thousand to well over ten thousand cubic meters per month and borehole are common here. However, it has been shown that, under certain geological conditions, pressing large volumes can trigger (“trigger”) earthquakes . For this purpose, a fault that is appropriately oriented in the regional tectonic stress field must be located near the injection point, so that the increased pore pressure propagates up to this fault and there a "fault slip" (movement of the two wings of the fault against each other) as a result of the lowering the static frictional force on the fault surfaces, and thus can trigger an earthquake. The strongest earthquake for a long time, the generally accepted cause of which was wastewater injection, occurred on August 9, 1967 near Denver . The wastewater came from the chemical weapons manufacturing process . The magnitude at the time was 4.8. In the course of the fracking boom in the USA, this value has already been exceeded several times, for example on August 23, 2011 near Trinidad in the Raton Basin ( Colorado ) with a magnitude of 5.3 and three times between November 5 and 8, 2011 near Prague ( Oklahoma ). The strongest of these three quakes (November 6th), with a magnitude of 5.7, is the strongest event ever associated with wastewater injection. Several single-family houses were completely destroyed by this quake. The extraction of fossil hydrocarbons from unconventional storage sites by means of fracking generates significantly more polluted wastewater than conventional extraction.

When potash mining in the Werra potash district fall per year to some 13 million cubic meters of caustic potash, of which about 5 million cubic meters in dolomite ( line sequence , Zechstein ) are pressed, the layered depth between 150 and 500 meters. However, either the lye does not stay in the target horizon or it displaces saline deep groundwater into aquifers near the surface that are used for drinking water, which is why numerous drinking water extraction points have already had to be closed. Residents and environmental associations are therefore calling for the caustic press to be stopped.

Individual evidence

  1. ↑ Hans-Jürgen Kretzschmar, Volker Köckritz: CO 2 storage underground. Journal for friends and sponsors of the TU Bergakademie Freiberg. 17th year, 2010, pp. 33–39 ( PDF 5.5 MB, complete issue)
  2. ^ A b William L. Ellsworth: Injection-Induced Earthquakes . In: Science . tape 341 , 2013, doi : 10.1126 / science.1225942 .
  3. ^ David M. Evans: The Denver Area Earthquakes and the Rocky Mountain Arsenal Disposal Well. In: The Mountain Geologist. Vol. 3, 1966, doi: 10.1785 / 0120140009
  4. ↑ Justin L. Rubinstein, William L. Ellsworth, Arthur McGarr, Harley M. Benz: The 2001 – Present Induced Earthquake Sequence in the Raton Basin of Northern New Mexico and Southern Colorado. In: Bulletin of the Seismological Society of America. Vol. 104, No. 5, 2014, doi: 10.1785 / 0120140009
  5. ↑ Katie M. Keranen, Heather M. Savage, Geoffrey A. Abers, and Elizabeth S. Cochran: Potentially induced earthquakes in Oklahoma, USA: links between wastewater injection and the 2011 M W 5.7 earthquake sequence. In: Geology. Vol. 41, No. 6, 2013, pp. 699–702, doi: 10.1130 / G34045.1 (alternative full text access : USGS ( memento from January 10, 2015 in the Internet Archive ))
  6. ↑ Ulf Frank, Alexander Reitinger: Injection of salt wastewater from potash production in saline aquifers - practical experience as a drinking water supplier with underground storage. Powerpoint presentation ( PDF 2.0 MB)