WDA Consultants Inc.

Tademait Plateau: A regional groundwater recharge area in the centre of the Algerian Sahara

K.U. Weyer 1), Franz May 2), and James C. Ellis 1)
1) WDA Consultants Inc. Calgary, Canada: weyer@wda-consultants.com
2) BGR, Federal Institute for Geosciences and Natural Resources, Hannover, Germany

Text version of poster presented at the Third EAGE CO2 Geological Storage Workshop, Edinburgh, UK, March 26-27, 2012.

© 2012, WDA Consultants Inc.


Geologic storage of CO2 is often seen as a static system whereby the CO2 is kept in storage by the "impermeable" caprock. Only vertical buoyancy forces would act upon the stored CO2 in reservoirs. For saline aquifers it is claimed that the addition of CO2 increases the density of the saline water and this would cause the CO2-enriched saline water to move downward to the bottom of sedimentary basins where it would be safely stored for millions of years. All these assumptions are incorrect as can be shown by applying the physics of Hubbert’s (1940) Force Potential to CCS (Weyer, 2010). Weyer (2010) also showed that flowing groundwater would dissolve stored CO2 and carry it along its flow path to regional groundwater discharge areas. There, salty and CO2-containing water would, in minor amounts, discharge from below into the centre of rivers and lakes (compare Fig. 1 and 2) .

Crystal Geyser, Utah
Figure 1: Natural discharge of CO2 at the Crystal Geyser on the bank of the Green River, Utah, as the end point of a large-scale regional groundwater flow system. (Picture by Weyer, Feb 2010).

sand model
Figure 2: Model demonstration of deep groundwater flow with a plume of dissolved CO2 entering a surface water body from underneath.

As groundwater flow systems reach to great depth by penetrating aquitards (caprocks), any successful design of on-shore geological carbon storage must regard the migration effects groundwater flow systems exert on stored CO2. In most cases all of the CO2 will be dissolved by groundwater and migrate to the discharge areas of these flow systems.

Deep groundwater flow will transport the dissolved CO2 towards groundwater discharge areas and thereby into surface waters. A telling example of such a system is the Green River in Utah with its natural discharge points of natural CO2 and the artificial discharge point Crystal Geyser, a flowing abandoned well located at the bank of the Green River (Fig. 1). Fig. 2 shows the manner in which the abandoned flowing well at the Green River intersects the CO2 plume (red colour). Comparing both figures, the upward flow of the CO2-containing groundwater is indicated by the artesian discharge in wells close to the surface water bodies.

Hydrogeological tools have been developed which allow the determination of the flow paths of deep groundwater flow systems and the approximate time scale to reach their groundwater discharge areas. These time spans may reach orders of magnitude of tens of thousands of years and the amount of CO2- rich groundwater entering the surface water will be miniscule in comparison to the volume of surface water flow. Therefore no major environmental impacts are anticipated (Weyer, 2010). Residence times in the thousands of years or more would in all likelihood suffice in mitigating any atmospheric effect caused by the discharge of CO2.

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