In addition to its reserves of coal, natural gas and petroleum, southern Germany has particularly high geothermal potential along the Upper Rhine rift valley and the Molasse basin, which can be harnessed to meet the baseload supply of heat and electricity. Several power-plant prototypes are already operational, confirming the great potential capacity of the systems. In the highly industrialized region of southern Germany, a shortfall is anticipated in the electricity supply, and geothermal energy provides a genuine opportunity to cover this gap using local renewable resources. The Steinbeis Transfer Center for Geoenergy and Reservoir Technology works to advance environmentally friendly use of these technologies.
The current transition to innovative alternative-energy technologies presents a major challenge to society and the scientific community. As in the past, geothermal energy is expected to make a major contribution to supplying our society with energy.
In 2010, fossil fuels comprised over 80 % of primary energy in Germany, and over 50 % of them consist of hydrocarbons (petroleum, natural gas). The prognosis for the energy mix in 2030 indicates only a minor reduction in this constellation. Given the current developments in Germany‘s energy policy, this forecast will soon have to be revised upward. Awareness of growing energy scarcity will trigger price increases, as will dependence on foreign resources, and this in turn will give rise to doubts about the security of our energy supply. More investments will be necessary to exploit new resources, and this will lead to new exploration measures in Germany as well.
Geoenergy, also called geothermal energy, requires a comprehensive energy management plan which encompasses the use, management and storage of energy sources found in subterranean formations. Transitioning to new geotechnologies means reservoirs will have to be developed in dense and fractured media, and consequently, this field is becoming more relevant from a scientific perspective as well. The focus is on fundamental issues of environmentally friendly development of areas such as geothermal reservoirs. When it comes to generating geothermal energy, there are important environmental questions to be answered about induced seismicity, the use of chemicals and avoiding radioactive deposits in geothermal systems.
Creating microquakes by means of hydraulic fracturing (i.e., forcing water underground) is an important point of reference in determining the need to enhance reservoir properties. Induced seismicity, as it is known, can take place at the beginning of the geothermal project immediately after drilling, and these measures can only occur within a few days. The volume and success of the outcome can be tracked by means of induced seismicity. Scientists are focusing on controlling the intensity of the seismicity. Events which trigger microquakes can release forces which are detectable on the earth‘s surface and have the potential to damage structures aboveground. Progress has been made in terms of preventing the tangible effects of induced seismicity, especially in regard to controlling the pressure at which the water is pressed into the rock. This can occur during reservoir stimulation by administering high pressure for limited periods. During operations, it can occur by re-feeding thermal water back into several boreholes such as relief holes. One unresolved questioned to date deals with handling the changes in pressure caused by sudden and unforeseen events such as abruptly interrupting operations.
Chemicals are also used to improve the efficiency of the subterranean geothermal water circuit. Like hydraulic stimulation, the chemical stimulation of a reservoir is limited to the initial phase immediately after drilling, and in this case, it can only last a few hours. As a rule, the main priority is the connection between the different deep boreholes and the reservoir. Chemicals are used to dissolve the minerals which can constrict or close off the flow to the boreholes. Different substances are used depending on the mineral in question. For example, calcite can be treated with diluted hydrochloric acid. Unlike other geotechnologies, the chemicals cannot be fed back; instead, the reaction products (in this case CaCl, CO2 and water) remain underground. The scientific challenges in this area include the use of biodegradable products and the integrity of the boreholes.
When a power plant is operated, mineral deposits should not be allowed to accumulate in the aboveground parts of a geothermal system. The objective is to return everything back underground which the productionrelated drilling brings to the earth‘s surface; the only thing to be taken from thermal water is heat. However, the fluctuations in the water temperature can in fact cause chemical reactions (mineral precipitations) within the aboveground closed system. Different substances are used to prevent precipitation; they must be chosen very deliberately based on the chemical composition of the thermal water. The challenge is choosing products which will not cause corrosive damage to the aboveground installations and/or the steel pipes of the drillings. Another concern is that the naturally occurring radioactive minerals (NORMs) which are brought to the surface with the thermal water in naturally occurring quantities are not retained in the mineral deposits and thus remain on the earth‘s surface. Currently, intense research is being conducted on these issues.
A variety of different scientific partners are now working to develop environmentally friendly applications for geothermal energy technologies. The Steinbeis Transfer Center for Geoenergy and Reservoir Technology is in charge of implementing this process in conjunction with the industry. From the planning phase onward, the center works hand in hand with its partners to develop ideal sites with a lower need for stimulation measures. This is intended to increase the acceptance of the technology among the general public in Germany.
Dr. Eva Schill
Steinbeis Transfer Center for Geoenergy and Reservoir Technology (Lottstetten-Nack)