Markus Ebert

Impacts of the use of the geological subsurface for energy storage: an investigation concept

New methods and technologies for energy storage are required to make a transitionto renewable energy sources; in Germany this transition is termed “Energiewende”. Subsurface georeservoirs, such as salt caverns for hydrogen, compressed air, and methane storage or porous formations for heat and gas storage, offer the possibility of hosting large amounts of energy. When employing these geological storage facilities, an adequate system and process understanding is essential in order to characterize and to predict the complex and interacting effects on other types of subsurface use and on protected entities. In order to make optimal use of georeservoirs, a comprehensive use planning of the subsurface is required that allocates specific uses to appropriate subsurface locations. This paper presents a generic methodology on how subsurface use planning can be conducted and how its scientific basis can be developed. Although synthetic, realistic scenarios for the use of the geological underground for energy storage are parameterized and numerically simulated, accounting for other kinds of subsurface use already in place. From these scenario analyses, the imposed coupled hydraulic, thermal, mechanical and chemical processes, as well as mutual effects and influences on protected entities are assessed and generalized. Based on these, a first methodology for large-scale planning of the geological subsurface considering different surface and subsurface usage scenarios may also be derived.

Modeling, parameterization and evaluation of monitoring methods for CO2 storage in deep saline formations: the CO2-MoPa project

Capture and geological sequestration of CO2 from large industrial sources is considered a measure for reducing anthropogenic emissions of CO2 and thus mitigating climate change. One of the main storage options proposed are deep saline formations, as they provide the largest potential storage capacities among the geologic options. A thorough assessment of this type of storage site therefore is required. The CO2-MoPa project aims at contributing to the dimensioning of CO2 storage projects and to evaluating monitoring methods for CO2 injection by an integrated approach. For this, virtual, but realistic test sites are designed geometrically and fully parameterized. Numerical process models are developed and then used to simulate the effects of a CO2 injection into the virtual test sites. Because the parameterization of the virtual sites is known completely, investigation as well as monitoring methods can be closely examined and evaluated by comparing the virtual monitoring result with the simulation. To this end, the monitoring or investigation method is also simulated, and the (virtual) measurements are recorded and evaluated like real data. Application to a synthetic site typical for the north German basin showed that pressure response has to be evaluated taking into account the layered structure of the storage system. Microgravimetric measurements are found to be promising for detecting the CO2 phase distribution. A combination of seismic and geoelectric measurements can be used to constrain the CO2 phase distribution for the anticline system used in the synthetic site.

Energy storage in the geological subsurface: dimensioning, risk analysis and spatial planning: the ANGUS+ project

New techniques and methods for energy storage are required for the transition to a renewable power supply, termed “Energiewende” in Germany. Energy storage in the geological subsurface provides large potential capacities to bridge temporal gaps between periods of production of solar or wind power and consumer demand and may also help to relieve the power grids. Storage options include storage of synthetic methane, hydrogen or compressed air in salt caverns or porous formations as well as heat storage in porous formations. In the ANGUS+ project, heat and gas storage in porous media and salt caverns and aspects of their use on subsurface spatial planning concepts are investigated. The optimal dimensioning of storage sites, the achievable charging and discharging rates and the effective storage capacity as well as the induced thermal, hydraulic, mechanical, geochemical and microbial effects are studied. The geological structures, the surface energy infrastructure and the governing processes are parameterized, using either literature data or own experimental studies. Numerical modeling tools are developed for the simulation of realistically defined synthetic storage scenarios. The feasible dimensioning of storage applications is assessed in site-specific numerical scenario analyses, and the related spatial extents and time scales of induced effects connected with the respective storage application are quantified. Additionally, geophysical monitoring methods, which allow for a better spatial resolution of the storage operation, induced effects or leakages, are evaluated based on these scenario simulations. Methods for the assessment of such subsurface geological storage sites are thus developed, which account for the spatial extension of the subsurface operation itself as well as its induced effects and the spatial requirements of adequate monitoring methods.

Kinetics of oxygen release from ORC

ABSTRACT Oxygen release compounds (ORC) are one possibility to enhance aerobic degradation in contaminated aquifers. However, some applications have been reported where oxygen concentrations did not meet expectations, this was attributed to ground water composition, e.g., high pH. Column experiments have been performed and the measurements were interpreted using a numerical model to investigate oxygen release kinetics from ORC in more detail. Because the zero-order rate law recommended by the manufacturer did not reflect the measurements, a more complex kinetic scheme was developed. The simulations show a minor influence of inorganic ground water constituents on oxygen release from ORC in the columns due to buffering by mineral precipitation, but an enhanced oxygen release if aerobic degradation takes place. If ORC is applied as socks, the impact of inorganic ground water composition increases compared to the application in column experiments. A simple quadratic equation is provided to estimate oxygen release rate from the buffer capacity of the ground water versus increasing pH—a parameter easily determinable in the laboratory. For slightly mineralized waters with high pH, this equation forecasts decreased oxygen release, but no total inhibition of oxygen release.

Geochemical Effects of Millimolar Hydrogen Concentrations in Groundwater: An Experimental Study in the Context of Subsurface Hydrogen Storage

Hydrogen storage in geological formations is one of the most promising technologies for balancing major fluctuations between energy supply from renewable energy plants and energy demand of customers. If hydrogen gas is stored in a porous medium or if it leaks into a shallow aquifer, redox reactions can oxidize hydrogen and reduce electron acceptors such as nitrate, FeIII and MnIV (hydro)oxides, sulfate, and carbonate. These reactions are of key significance, because they can cause unintentional losses in hydrogen stored in porous media and they also can cause unwanted changes in the composition of protected potable groundwater. To represent an aquifer environment enclosing a hydrogen plume, laboratory experiments using sediment-filled columns were constructed and percolated by groundwater in equilibrium with high (2-15 bar) hydrogen partial pressures. Here, we show that hydrogen is consumed rapidly in these experiments via sulfate reduction (18 ± 5 μM h-1) and acetate production (0.030 ± 0.006 h-1), while no methanogenesis took place. The observed reaction rates were independent from the partial pressure of hydrogen and hydrogen consumption only stopped in supplemental microcosm experiments where salinity was increased above 35 g L-1. The outcomes presented here are implemented for planning the sustainable use of the subsurface space within the ANGUS+ project.

Degradation of Organic Groundwater Contaminants: Redox Processes and EH-Values

In many cases the EH-value of a groundwater sample is either measured or calculated from the distribution of certain redox couples, with the result that the utility of the resulting value is small. The selective sensitivity of the redox electrodes (Lindberg & Runnells, 1984), partial non-equilibrium and the resulting mixture of potentials (Stumm & Morgan, 1996), or an insufficient preparation of the probes (e.g. Kolling, 1986) are made responsible for the uncertainty of this “weak” milieu parameter. Especially in sulfidic environments often too high EH-values are found. The insensitivity of the platinum redox electrodes for the sulfide/sulfate redox couple are surely responsible for this.