Our expertise is based on many years in interdisciplinary research with holistic and sustainable approaches. The following clusters are established within the section:
Knowledge of the subsurface thermal conditions is of paramount importance for the evaluation of geo-resources.Thus the characterization of thermo-hydraulic rock properties and of effective heat-transport processes is essential part of advanced exploration technologies for these resources.
Especiallyin geothermal exploration, the success rates of identifying new geothermal resources can be increased and the risk and development costs can be lowered through implementing pertinent data on heat sources dimensions and geometry as well as thermal rock properties into advanced conceptual models.
Research focuses on both the thermal parameters at lithospheric scale and more specific also on those in the depth domain that can be explored by borehole drilling. Furthermore, we characterize the thermal field and thermal rock parameters at regional as well as local scale, the latter of which directly feed into the development of hydrothermal and petrothermal (EGS/HDR) energy projects. We use data from borehole and surface geophysical surveys, analyze chemical and physical rock properties and develop numerical, geology-assisted subsurface models down the base of the Earth crust by working at the interface of pure and applied geothermics.
Our expertise has developed during work performed in different geodynamic settings in the world, e.g. in the North German Basin, the Erzgebirge and Luxembourg in Europe, the North American Midcontinent, the Andean subductionzone in Bolivia and Chile, the Arabian Shield in Israel and Jordan, as well as in India.
Porosity, density, gamma-ray intensity and temperature measured in boreholes are some of the parameters that we use in the evaluation of the geology and the temperature field. They are also used in the fashion of integrated core-log interpretation to feed subsurface models. Furthermore, geophysical well-logging data are deployed in novel approaches to indirectly determine thermal rock properties. The application of those approaches opens new possibilities for the parametrization of numerical temperature models.
The heat-flow density is an intrinsic parameter for all temperature models, for which it is used either as input or for calibration. Its determination requires a high-precision temperature log under thermal equilibrium in conjunction with the rock thermal conductivity of the studied depth interval. We have experience in performing heat-flow studies including the identification of different modes of heat transfer and of heat generation processes.
We measure the thermal conductivity and thermal diffusivity of dry and saturated rocks at ambient conditions using different laboratory devices. We also investigate the feasibility of calculating the thermal conductivity from the modal mineralogy of a rock. A laboratory device is in the making allowing for dry or saturated rocks measurements of thermal conductivity at pressures and temperatures that are simultaneously raised to 200 MPa and 200°C, respectively.
The comprehensive understanding of the subsurface condition is a pre-requisite for a precise planning and a successful operating of geothermal applications. Our exploration concept incorporates methods from several branches of geosciences: geophysics, geology, geochemistry, hydrogeology and pure geothermics (including heat flow and temperature studies). We are working cross the scales, from microscale to the reservoir scale, integrating available data and generating new one where necessary. The selection and application of our exploration methods is strongly dependent on the geological setting and data availability from former exploration campaigns.
Based on their energy content, geothermal resources could be classified as high-enthalpy resources, medium-enthalpy resources, and low-enthalpy resources. While high-enthalpy resources are often located near plate boundaries and zones with active volcanism, low-enthalpy resources are preferentially found in older sedimentary basins of the continents. The success of geothermal exploitation concepts strongly depends on the heat transport processes involved (conduction, convection or hydraulic permeability). For the characterization and assessment of geothermal resources we combine geological, geophysical and geochemical methods and integrate their respective results in geological models. The integration is performed by interdisciplinary cross-scale interpretation resulting in consistent parameterized (scale-dependent) structural models. In this way, locations can be characterized reliably and risks for the development and operation of geothermal plants could be minimized.
Systematic and area-wide study of gases and emanations at the geosphere-atmosphere interface is an important approach for geothermal system analysis. Soil gas composition and flux rates of gases indicate potential fluid pathways and provide insights into processes at depth and on its way to the surface. Results of our field studies contribute to an improved understanding of geothermal systems, not only for geothermal exploration and assessment, but also for monitoring purposes. The interdisciplinary combination of soil gas data with other relevant scientific disciplines is one of our key objectives.
For a successful characterisation of geothermal sites, all available geological and geophysical data must be matched in parameterized structural models. These models are used for the planning and operation of geothermal plants. On the other hand, observations of unexpected changes in reservoir properties can only be understood if a reliable and adequate site characterization is available. We create these models and measure, if necessary, additional data for their parameterization and examine their scale dependency. Using field observations, we investigate differences from model-based predictions and examine site-specific approaches to adapt both: the parameterization of the model and future exploration and monitoring concepts.
Geothermal fluids are the transport media for subsurface heat, and, therefore, the essential substance of geothermal energy production. They consist of a mixture of gas and condensed phases with complex chemical compositions. An exact understanding of the physical properties and chemical tendencies of these fluids are necessary for modeling the many processes occurring during fluid transport. Such models are required for minimizing risk and improving plant sustainability.
The competency cluster “Fluids” is involved in researching the chemical behavior and physical properties of geothermal fluids. The cluster is also responsible for online fluid and gas monitoring at the research platform Groß Schönebeck. The working group has an analytical-experimental orientation and possesses several laboratories, wherein measurements and experiments can be performed at in-situ reservoir conditions.
Interdisciplinary work with other research groups at the ICGR is performed, for example, in the areas of corrosion and scaling, fluid-rock interactions and thermodynamic parameterdetermination for reservoir modeling. We research an assortment of topics in cooperation with several national and international project partners.
Mineral deposition in the components of a geothermal power plant or the pore space of a rock formation can significantly inhibit fluid production. The goal of our research is to understand the chemical processes that lead to mineral deposition and to develop methods to manage this issue in a working power plant. Our laboratory is equipped to simulate complex processes in geothermal brines in well-defined solutions, whereby the solubility and precipitation rates of various minerals can be studied.
Of central importance to the sustainable operation of a geothermal power plant is knowledge of the geothermal fluid’s physical properties, such as density, viscosity, ultrasonic velocity, electrical & thermal conductivity and heat capacity. Our laboratory is designed for determining these properties in highly saline fluids at conditions commonly found in geothermal reservoirs.Results from our research are used to expand existing databases for the thermodynamic properties of geothermal fluids.
At the research platform Groß Schönebeck, we operate the fluid-monitoring system, “FluMo.” The system allows for the determination of relevant physico-chemical parameters in geothermal fluids directly within the geothermal circuit. The system also allows for fluid sampling at various points along the circuit. The FluMo system can support the sustainable operation of a geothermal power plant by monitoring changes in the geothermal fluid’s chemistry online and in real-time.
Scientific themes in rock physics are experimentally focused and relate to interrelations between physical properties of rock and its inner structure.
The research topics we address result from sustainable use of geothermal energy, carbon dioxide sequestration, and the use of natural methane hydrate deposits. In addition to characterizing a rock’s actual state investigations on dynamic processes and time-dependent physical changes are conducted. All experiments are performed under controlled pressure and temperature conditions that represent possible in situ conditions during reservoir use. Our experimental methodology is continuously developed further to conduct experiments at progressively more extreme, e.g. supercritical, conditions. Linking reservoir exploration and exploitation of geological reservoirs our scientific results contribute to their sustainable use.
Measurements of physical rock properties under simulated in situ conditions are central to an integrated characterization of geological reservoirs. On a routine basis we operate experimental apparatuses and devices to investigate seismic, electrical, and hydraulic properties of water-saturated rock samples at controlled confining pressures up to 300 MPa, pore pressures up to 100 MPa and maximum temperatures of 250°C.
Production and injection of fluids from and into the subsurface, respectively, yield changes in the thermodynamic and chemical state of a reservoir. As a consequence, fluid-rock interactions are induced that may alter the rock’s physical properties. To predict the long-term behavior of reservoirs during and after use we conduct laboratory investigations at simulated reservoir conditions.
To cope with challenges of new research tasks existing methods are developed further and new experimental setups are constructed. Many unique apparatuses thus emerge capable of measuring a number of physical rock properties at simulated conditions of the earth’s crust. A challenge, e.g., is the extension of the experimentally usable temperature range to 400°C and beyond as encountered in ultra hot geothermal reservoirs.
An economic use of geothermal reservoirs requires analysis of the geological system, including chemical and petrophysical reservoir characterization, reservoir stimulation and modelling as well as understanding of the interaction in the borehole-reservoir system.
Reservoir-Engineering is essential for an appropriate development of geothermal resources. Optimum economic utilization of geothermal reservoirs requires analysis of the geological system together with adequate planning. These include chemical and petropysical reservoir characterization, reservoir stimulation and modelling as well as understanding of the processes and interaction of the borehole-reservoir system. The control of the amount of fluids produced, well path design, well placement, rate of injection and many other means help to optimize the heat recovery.The reservoir engineer estimates the heat in place, the thermal breakthrough time and optimize the reservoir performance by four major activities: observations, assumptions, calculations (analytical and numerical methods) and development decisions.The research wells drilled by GFZ at Groß Schönebeck make possible to access and circulate formation fluids in the horizons between 3,9 and 4,4 km at temperatures up to 150 °C. This downhole laboratory provides the opportunity to perform various borehole measurements and in situ experiments, to validate and improve model in use or develop new ones.
Stimulation treatments are an option to enhance the productivity of low permeability geothermal reservoirs by inducing artificial fluid pathways.
At GFZ specific stimulation treatments have been developed to enhance the existing permeability; i. e. hydraulic fracturing, thermally induced fracturing and chemical/ acid stimulation.
In hydraulic stimulation experiments, fluids are injected under high pressure into the subsurface rocks to create new fractures or extend existing fractures.
Effective energy production from geothermal reservoirs requires that the physical properties of the host rock have to be characterized as precisely as possible. Additionally, rock physical experiments provide a valuable complementary method to investigate particular processes associated with mechanical and thermodynamic changes induced during operation. The results of such investigations improve the outcome of hydro-thermo-mechanical-chemical simulation codes in order to derive statements on reservoir productivity, sustainability, and best-practice operation.
An appropriate numerical model is important for planning the well path and fracture design, interpreting hydraulic tests and stimulations, and predicting reservoir behavior during geothermal power production.
Such models should include:
(i) the reservoir geology and structure,
(ii) the geometry of wells and fractures and
(iii) the hydraulic, thermal, mechanical and chemical conditions of the reservoir and fractures generated due to changes in reservoir conditions.
The reservoir monitoring cluster studies natural and artificially induced flow processes within the subsurface. Within field experiments innovative borehole measurement methods are applied and developed.
We investigate the effects of natural and artificially induced flow processes within the subsurface. Innovative borehole measurement methods are developed and applied within field experiments. The integration with other geophysical and geochemical methods enables a quantitative registration of spatial and temporal changes of subsurface conditions and reservoir properties.
We work on methods which are specially tuned to the requirements of new types of subsurface use, like new ways of extracting geothermal energy (e.g. enhanced geothermal systems, supercritical reservoirs), underground storage (e.g. carbon dioxide, thermal energy), or production of unconventional fossil fuels (e.g. gas hydrates). Moreover novel methods for monitoring of borehole integrity (e.g. cementation) are developed. The measured data enables to derive important information for the safe and efficient use of geological reservoirs.
Fluid movement in the subsurface can be quantified by measuring pressure, temperature, as well as flow velocities along a flowing well. A novel hybrid borehole logging system was developed to allow for a combined deployment of fiber-optic and electronic sensors. With our current wireline logging equipment, measurements down to well depths of 6000 m and temperatures of 150°C can be performed.
In order to detect dynamic processes within the subsurface and to evaluate the structural wellbore integrity, custom designed cables can be permanently installed along the tubing or behind casing. Together with industry partners, suitable downhole sensing equipment and installation techniques are developed for the deployment in deep wells. Within previous research projects, we have installed permanent sensor cables within wells at depths of up to 1200 m and operating temperatures above 300°C.
Distributed sensing techniques like DTS (distributed temperature sensing) or DAS (distributed acoustic sensing) enable new possibilities for borehole monitoring, as they allow for quasi-continuous acquisition of data over several-km distances with high spatial and temporal resolution. In collaboration with partners from academia and industry we develop novel fiber-optic sensors for measurement of additional physical and chemical parameters in laboratory and field applications.
Use of the subsurface for energy production and storage is an important component of future-oriented and sustainable energy supply.
By accessing geothermal resources it is possible to use stored heat from the deep subsurface for direct heat provision, to transfer the heat to a higher or lower (“cold”) temperature level using appropriate techniques, or to convert it into electricity. For conversion into electricity, typically, power plant cycles applying the Clausius-Rankine or a modified Clausius-Rankine process are used. Although the use of geothermal heat for production or storage of energy is based on the same thermodynamic processes as in conventional energy engineering, most importantly, effects of geological conditions have to be considered and adjusted design algorithms as well as optimization strategies have to be developed. The competence cluster “Process and Plant Technologies” is concerned with investigations on energy and process technological aspects of subsurface use as part of a sustainable energy supply. Our research applies to the fields of energy and process engineering, materials selection as well as test and pilot plant engineering which also includes related economic and ecological aspects.
The aim in process engineering is reliable production and injection of generally highly mineralized and polyphase deep thermal fluids. A prerequisite for reliable setup and operation of a thermal fluid loop is the selection of suitable components as well as operational parameters. In ongoing research projects, therefore, the response of various materials to corrosive environments as well as scaling processes and degassing are experimentally and numerically investigated.
The energetic use of geothermal resources requires the development of suitable technical plant concepts as these do not as yet constitute an established standard. The focus at GFZ is the adaptation of existing technical components and the development of suitable design approaches that permit an optimal coaction of components in plants for deep geothermal systems. The ultimate goal is to improve sustainability and reliability as well as efficiency of the overall system.
Energy supply systems comprising aquifers consist of several subsystems: the reservoir, the plant, and the users determining the structure of energy demand. The GFZ is concerned with improving the reliability and efficiency of such systems in the framework of a holistic approach. Central site for the investigations as of today are the German parliamentary buildings in Berlin which are, among others, energetically supplied by two aquifers below ground for heat and cold, respectively.