In August, GeoForschungsZentrum (GFZ) Potsdam, Germany’s National Laboratory for Geosciences started a new series of experiments at its geothermal research site at Gross Schönebeck near Berlin.
In these so-called hydraulic fracturing experiments, huge amounts of water are being pressed under high pressure into the ground via a 4.4km deep well bore. Natural fractures and fissures will be widened as a result of the water pressure and new flow paths generated.
Similar tests have already been successfully performed in a second well at Gross Schönebeck in 2003, when 12m litres of water were pumped underground. The latest experiments are aiming to use geothermal energy not just for heating purposes, but also for generating electricity. For this, hot natural water will be produced from one well, utilised in a future geothermal power plant, and then pumped back underground through a second well bore: in other words, a closed water circle.
“Under the local geological conditions, the minimum temperature of 150°C necessary for electrical power generation is only found at a depth in excess of 4km. Under these conditions, as much natural hot water has to be produced from the well as possible in order to operate a geothermal power plant successfully,” said project manager Ernst Huenges of GFZ Potsdam. Explaining the need for hydraulic fracturing, he added: “The more permeable the underground rocks are, the more water flows through the reservoir into the production well.”
The stimulation will be performed in three injection phases in various rock layers. Huenges offers reassurance that such activity will not cause any earthquakes: “We have performed similar experiments in 2003 at the same location, where sedimentary rocks are typical for the North German basin, without any recognisable seismicity.”
Even so, the progress of the hydro-fracturing experiments will be monitored by highly-sensitive seismic monitoring instruments. A later, long-term experiment between the two wells will be used to prove whether or not the stimulation has been a success and whether or not water flow rates have increased.
GFZ Potsdam has been carrying out scientific experiments and investigations into geothermal electrical power generation since 2001. A natural gas well from the 1990s was reopened for this purpose and increased in depth to 4.3km. The second well in which the current experiments are taking place was completed in January this year.
This latest initiative is part of a twin approach to geothermal technology that is being pursued by the organisation.
The main task of the first part is to create innovative methods of geothermal exploration. “Geophysical survey methods are currently capable of depicting subsurface geological structures. However, knowledge about the reservoir properties of the target horizons is the information most needed. The solution lies in the combination of various geophysical methods describing the subsurface with laboratory experiments on rocks,” says GFZ Potsdam.
Such an integrated interpretation will use laboratory experiments on the reservoir rocks under in-situ conditions (temperature and pressure) to gain knowledge of material properties. These are incorporated into dynamic models of the temperature and flow field and their evolution with time and are complemented with measurements in boreholes as well as surface geophysical surveys in the vicinity of these boreholes. In this manner, says the organisation, all spatial and temporal scales of the system can be considered.
These activities are planned and will be performed in close cooperation with other research institutes and industrial partners. One example is the investigation of the deep flow field in the North German Basin and an international project will study the fluid phase conditions (liquid and steam) in the vapour-dominated geothermal resources in Tuscany, Italy
Meanwhile, the second part of the research focuses on reliable operation of the thermal fluid cycle and warranted energy supply, including the conversion of low-enthalpy heat into electricity.
New methods are needed to observe and study subsurface and surface processes associated with the transport of geothermal fluid. Understanding in detail how the various components in the geothermal fluid affect the machinery encountered in the cycle is essential to avoid undesirable processes such as corrosion of parts of the machinery or clogging of injection wells by precipitation and deposition of minerals.
The chemical composition and possible multiphase flow call for utmost care in the selection of materials and for an adjustment of process parameters in the apparatuses of the power plant (temperature and pressure). Innovative monitoring systems are needed to observe processes in real time and to allow for immediate reaction to changes in the system, concludes the organisation.
Be The First To Comment