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Redefining geothermal fluid properties at extreme conditions to optimize future geothermal energy extraction

Periodic Reporting for period 1 - REFLECT (Redefining geothermal fluid properties at extreme conditions to optimize future geothermal energy extraction)

Reporting period: 2020-01-01 to 2021-06-30

Climate change and the energy transition require a transformation of the energy market. But in order to achieve the medium-term goals of the Paris Climate Agreement, sustainable solutions for energy supply have to be further developed, especially with regard to their economic viability. Geothermal energy is a renewable and base-load compatible form of energy that is able to compensate the weaknesses of other, weather-depending or seasonal forms of renewable energy. However, a large part of the potential of geothermal energy production remains unused, because of the technical challenges of its utilization.

The one problem plaguing almost all deep geothermal operations in the world is related to the chemistry of the geothermal fluids. In order to maximise both, the operational efficiency and economic returns of geothermal power plants, it is vital that these systems work well for long periods without requiring significant maintenance. Key to this is preventing deleterious physical and chemical reactions such as degassing and mineral precipitation. Currently, accurate prediction of those reactions is difficult, due to poorly defined fluid properties, largely as a consequence of the difficulty in determining these properties at in-situ geothermal conditions (i.e. extremely hot or extremely saline fluids). REFLECT aims to address these challenges and redefine fluid properties through the acquisition of key new thermodynamic and kinetic reaction data thus facilitating optimisation of future geothermal energy extraction. Those data will be implemented in predictive models to determine fluid reactions at extreme conditions, and into a comprehensive European Fluid Atlas. This approach will result in a generic and transferable work-flow to significantly expand maintenance intervals for geothermal installations and thus reduce operational costs, increase well performance and lead to an increased number of economically viable geothermal projects.

The key objectives of the REFLECT project can be summarized as:
1. Extend databases (solubility, activity, reaction kinetics) to higher temperatures and higher salinities through lab experiments and modelling approaches
2. Determine the extent and location of the degasification front of geothermal fluids during production
3. Determine types of organic matter and microorganisms in various geothermal fluids and their effect on scaling and biofilm formation
4. Determine heat capacity, density, electrical and thermal conductivity, sonic velocity, and viscosity at various p, T, X
5. Develop a down-hole sampling technique suitable to collect fluid at chosen depth in hot and super-hot systems
6. Verification and implementation of the improved dataset by application in reactive transport modelling
7. Set up a geothermal Fluid Atlas that collates information on geothermal fluid properties across Europe together with their geological setting
Geothermal fluids have been sampled at 10 locations, for the high-temperature geothermal sites as well as for the high-salinity geothermal sites. Samples have been analysed regarding their inorganic chemical properties, organic compounds as well as microbiology.

In order to extend databases of solubility, activity, and reaction kinetics, three different high-temperature experimental setups have been verified. For one setup, which allows mineral solubility experiments up to 500 and 400 bar, initial testing has been performed.

The degassing of CO2 and N2 saturated water has been studied optically using a visual cell and a high-speed camera at elevated pressures (up to 100 bar) and temperatures (up to 100 °C). A new visual cell for use at more extreme conditions (up to 500 bar and 500 °C) has been constructed. These experiments will deliver gas dissolution constants which are necessary to determine the extent and location of the degasification front of geothermal fluids.

An extensive review of existing information on organic matter and microorganisms in geothermal fluids has been conducted and two related review papers are in preparation. The methods for the measurement and identification of microorganisms and organic matter have been validated and applied to samples collected during the first reporting period.

Concerning thermophysical properties, electrical conductivities of carbonate solutions at different concentrations are measured up to 450°C to determine limiting conductivities and association constants. Numerically, a new thermodynamic model for the H-Li-Na-K-Ca-Mg-Cl-H2O chemical system has been implemented with success in the PhreeSCALE geochemical calculation software to compute thermopysical properties.

In order to develop a high-temperature fluid sampler, the review of existing sampler designs has been completed and materials for the sampler have been selected. Component design, modular design of sampler and clock coupling mechanism are ongoing.

REFLECT researchers developed an open-source, generic, multi-scale package porousMedia4Foam where OpenFOAM® is coupled with PHREEQC to investigate hydro-geochemical interactions. The User’s guide for the software and a number of example applications as well as the software package itself are published in Deliverables D4.1 and D4.2. The workflow for uncertainty quantification in the fluid composition and its impact on scaling has been developed and tested in Task 4.2.

The European Fluid Atlas is a central element of the REFLECT project. Geothermal fluid data from 20 European countries have been collected (Deliverable 3.1).
REFLECT will extend the presently limited experimental data on the thermodynamic and thermophysical properties of high temperature brines for various salt contents. Using the knowledge on fluid properties generated in REFLECT, the range of application for geothermal energy conversion can be expanded to hotter and more saline conditions.

New technologies to anticipate fluid reactions and properties that are encountered in superhot geothermal environments are essential. REFLECT will develop a downhole sampling technique, which will enable fluid sampling from hot and super-hot wells.

Setting up a European Fluid Atlas that maps variations in fluid properties will facilitate the selection of new potential geothermal locations. To enable effective design and layout of new geothermal power plants it is critical that the geochemical fluid properties and processes can be anticipated.

Therefore, REFLECT will have a significant impact on the development of geothermal systems and on the overall electricity supply generated from renewable energy sources through:
• Increased technology performance and reduced maintenance costs leading to increased electricity output and faster amortization of the power plant due to reduced downtime and maintenance during operation,
• Reduced life-cycle environmental impact (reducing the release of non-condensable gases to the atmosphere by determining gas dissolution kinetics; minimizing the addition of chemicals (inhibitors) to the geothermal fluid for the prevention of scaling and corrosion)
• Facilitated exploitation of high-temperature geothermal resources

REFLECT’s main impact will thus be an improved EU energy security: By encouraging an increase of the share of geothermal energy within the European energy market, REFLECT can help to reduce the consumption of fossil fuels and reach the aims of the Paris agreement.
The REFLECT European Fluid Atlas includes geothermal fluid data from more than 20 European countries
Geothermal fluids have been sampled at 10 high-temperature and high-salinity geothermal sites.
Microscopic pictures of three microorganisms isolated from three different geothermal plants.
Experimental set-up for Silica solubility experiments as a function of temperature and sality.