Producing geothermal heat from production water causes cooldown from the reservoir temperature up to 250C at fluid pressures from over 100 bar to 10 bar.During the process degassification of CO2 and methane cause reduction in pH and by that dissolution and precipitation of minerals.At depth, mineral precipitation in the reservoir restricts flow paths through the cyclic system, resulting into injectivity loss, by that higher injection pressures result in additional costs.Due the large number of timesteps,numerically modeling mineralization, accounting for the reaction kinetics, can be computationally expensive. These simulations are less expensive when assuming a local equilibrium between the reactants and reaction-products. As described in Meulenbroek et all. (2020) we present an analytical model for mineral precipitation in a low-enthalpy geothermal reservoir.The three different reaction regimes are (1) fast reactions (2) very slow reactions (3) reaction/transport intermediate zone.We focus on the near-wellbore region in the reservoir, where precipitation can behave as a ‘skin’ and has a more dramatic impact on the injectivity than precipitation further downstream. Our numerical model uses a coupling approach between PHREEQC and COMSOL utilizing the qualification of the different reaction regimes. This methodology was validated by using an analytical solution of a specific mineralization case. In addition it was compared to a field case. @en

Microbially induced carbonate precipitation (MICP) through denitrification can potentially be applied as a bio-based ground improvement technique. Two strategies involving multiple batch treatments in a modified triaxial test setup were used to study the process efficiency. Both strategies aim to achieve 1 weight percentage (% by weight) of precipitated calcium carbonate (CaCO₃) and differ in number of flushes, hydraulic residence time, and substrate concentrations. In the experiment with few flushes and high substrate concentrations the microbial process was inhibited, only 0.28% by weight CaCO₃ was measured in the sand after 5 weeks of treatment. The regime with many flushes and low substrate concentrations stimulated microbial growth resulting in 0.65% by weight CaCO₃ within the same time period. Biomass growth and nitrogen gas production were stable throughout the experiment at low concentration, reducing the hydraulic conductivity of the sand, which eventually led to clogging. Precipitation rates up to 0.26% by weight/day CaCO₃ were observed. Applying a suitable substrate regime and residence time is important to limit inhibition and maintain the cell activity, allow for an efficient conversion, and generate a good precipitation rate.

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Adaptation planning for flood risk forms a significant part of global climate change response. Engineering responses to higher water levels can be prohibitively costly. Several recent studies emphasize the potential role of ecosystems in flood protection as adaptive risk reduction measures while also contributing to carbon fixation. Here, we use a conceptual model study to illustrate the built-in adaptive capability of ecosystems to reduce a wide range of wave heights, occurring at different water levels, to a narrower range. Our model shows that wave height of waves running through a forested section is independent of initial height or of water level. Although the underlying phenomenon of non-linear wave attenuation within coastal vegetation is well studied, implications of reducing variability in wave heights for design of ecosystem and levee combinations have not yet been properly outlined. Narrowing the range of wave heights by a vegetation field generates an adaptive levee that is robust to a whole range of external conditions rather than only to a maximum wave height. This feature can substantially reduce costs for retrofitting of levees under changing future wave climates. Thereby, in wave prone areas, inclusion of ecosystems into flood defense schemes constitutes an adaptive and safe alternative to only hard engineered flood risk measures.

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