The Third Sustainable Earth Sciences Conference and Exhibition

The H2STORE project is a BMBF founded collaborative project. The main objective of the subproject at the FSU Jena are investigations on experimentally induced mineralogical-geochemical variations in potential reservoir and caprocks affected by a H2/energy storage at depths. In this experiments samples from five different stratigraphic units, representing the major siliciclastic hydrocarbon reservoir units in Germany, are analyzed. These rocks differ in their time of deposition; facies and detrital composition; burial history and therefore in their diagenetic, pressure and temperature evolution over time and formation fluid compositions. To classify the effects of a potential H2/CO2 storage at depths different kind of sample material (plugs, thin sections and rock fragments < 3.0 mm) are used for autoclave batch experiments with induced H2 (CO2) exposure under reservoir conditions (p, T, synthetic formation fluid) for time periods of 4–6 weeks. Before and after the experiments the exactly same material was analyzed by light microscopy, FE-SEM, AFM and BET. Also formation fluid analyses before and after the experiments were investigated by ICP-MS and ICP-OES. Dissolution structures on mineral surfaces, an increase of the specific surface area and element enrichment in formation fluid indicate mineral dissolution of e.g. Ca (Mg)CO3 and CaSO4 during the experiments.

We would like to present a GIS-based 3D online planning tool for underground energy storage. Its aim is to provide a basis for a pre-selection of possible sites for thermal, electrical, and substantial underground energy storages. The primary task of the proposed tool is to assist local authorities when dealing with the security of energy supply regarding the safe subsurface energy storage in the German state of Schleswig-Holstein. Taking into account as many of the relevant input factors as possible, the tool aims to suggest appropriate sites for setting up a selected kind of underground energy storage. The data base incorporates the current situtation as well as different energy related future scenarios.

The system is implemented as an online 3D server GIS environment, with no software needed to be installed on the user side. The results, representing areas potentially suitable for underground energy storage, are visualized as interactive 3D graphics and 2D maps in the browser. They can be downloaded in Geomodelling and GIS file formats for integration into an existing workflow.

Cenozoic sediments of the North Sea Basin (NSB) have global importance for two reasons. Firstly, they record the glacial and interglacial history of environmental change in the Northern Hemisphere. Secondly, they overlie and seal operational and planned sites for the engineered storage of carbon dioxide (CO2), to store captured greenhouse gas emissions from power plant and industrial sources in Europe. Remarkably, the 1000 metre-thick Quaternary sediments are poorly sampled, bypassed to reach hydrocarbon resources in deeper strata.

This paper describes the work of the GlaciStore consortium who presents a revised seismostratigraphic model for the Quaternary strata of the NSB and studies of the extent of interconnecting, stacked networks of tunnel valleys. The consortium have used these studies to submit a drilling proposal to the International Ocean Discovery Program (IODP) where direct sampling will resolve the number of glacial cycles, improve understanding of groundwater layering and the implications of glacial landforms within the sequence, and quantification of geomechanical effects from fluctuating ice thicknesses (e.g. compaction, rock strength and stress profiles) on these sediments.

CO2 reinjection into a fractured reservoir is challenging, as reinjected CO2 may recycle rapidly to the gas production wells, leading to potential gas production losses.

Development studies require performing screening studies, looking at many possible scenarios (as geological model, well location, process capacity). It is hence critical to speed up the simulation time in order to be able to investigate these many scenarios.

Various fluid models, with various degrees of simplification, may be used to study different phenomena that will impact the CO2 break through time. This includes convective flow in the fracture network, CO2 diffusive flow into the gas bearing matrix blocks, and CO2 dissolution in the formation water.

Specific fluid models, embedded in the reservoir model, were used in order to look at the impact of these various phenomena for the different scenarios, in order to speed up the developement process. This is presented in more details for the modeling of the molecular diffusion into the matrix blocks and the modeling of the convective flow in the fractures.

This study describes injection of CO2 into a carbonate formation in the Middle East, which is considered as potential option for permanently storing CO2. It is predicted that CO2 predominantly migrates into a high permeability layer near the top of the reservoir and reaches a potentially conductive fault at the end of the injection period. Seepage of CO2 may occur along this fault during the post-injection period, causing upward migration of CO2 throughout the formation. The results show that CO2 dissolution and dissociation causes lowering of the pH to 4.7 in the plume, as well as some calcite dissolution. The molality of elemental Ca increases several orders of magnitude, although the amount of calcite dissolution remains limited. This suggests that the geochemical impact is relatively small in case of the closed system studied. The computed porosity changes are relatively larger than those computed for the SACROC carbonate reservoirs, where CO2 was injected for enhanced oil recovery. This is explained by mineral precipitation and possibly by higher initial Ca molalities in the SACROC modelling study.

Reactive transport simulations were performed in order to assess the impact of impure CO2 containing SO2 on the geochemical reservoir system in carbon capture and storage (CCS) scenarios. For the numerical computation the recently released code TOUGHREACT V3.0-OMP was applied. Special emphasis is given on the aqueous chemistry of SO2, which rapidly dissolves into the formation water. Therein two different models using a kinetic as well as a thermodynamic approach were included. These allow for evaluation of transport related effects, resulting in different spatial distribution patterns of SO2 and subsequent changing chemistry involving minerals, in particular carbonates. The main focus of the presented work lies on the systematic variation of selected input parameters and the sensitivity of the numerical results on these initial conditions. In summary, the most prominent parameters determining the geochemical changes of the reservoir system are the initial concentration of SO2 as well as the type and amount of carbonate minerals available for pH buffering.

The research of thermally loaded rocks and UTES were examined in a geological environment at temperatures about 90 °C. Long-term in-situ experiment was placed in the SP-47 adit in the Underground Research Laboratory Josef, Mokrsko, Central Bohemia. The elevated temperature reached distance 3 m far from a heater. At the end of the cooling the rock massif was cooled to the natural temperature (9 °C). The maximal efficiency was 23 %. Fluctuations in heating intensity induce rapid increase / relaxation of stress and strain in the rock massif. The extent of induced stress reaches farther than the extent of elevated temperature. Thermally induced strains are almost completely reversible. Only a surface of the rock may occur irreversible changes. Significant thermally induced stress is of the same order of magnitude as tensile strength of the bulk rock massif. Thermal load of the rock mass has a measurable effect on the hydraulic permeability of the rock environment and composition of the percolating underground water. Chemical composition of groundwater was influenced by the presence of Na-silicate based geopolymer and by the ambient properties (elevated temperature, evaporation, contact with air etc.) Hydraulic properties were influences by thermal stress and relaxation during the heating/cooling cycles.

Geochemistry plays a great role when assessing the impact of hydrogen storage. With the purpose of discovering and characterizing minerals-brine interactions as a consequence of hydrogen injection into a depleted gas reservoir, we constructed an equilibrium geochemical model using, GEM-Selektor (GEMS) package. A depleted gas reservoir from upper Austria, Molasse basin, has been selected as a candidate for hydrogen storage. Thermodynamic model of formation water and minerals at in situ condition (P = 107 bar, T = 40°C) was created to represent initial state of the system, then the system re-equilibrated by introducing hydrogen. Over the course of hydrogen injection, decreasing trend in the contribution of H2 to reactions in aqueous, gas, and mineral phases is observed, pH value increases immediately after hydrogen introduced into the system and interactions among minerals and brine are observed. Both minerals dissolution and precipitation are observed to maintain the equilibrium. Brine data reveal slight variations for aqueous species at the beginning of hydrogen injection and rapid changes when higher amount of hydrogen injected into the system. The results are achieved based on some assumptions such as considering hydrogen to be highly reactive and giving infinite time for reactions (equilibrium calculations).

In the course of planning and licensing, but likewise for the development and operation of deep geothermal systems, estimates of the frequency of exceedances of limits of ground motion are of interest. The limiting values used for evaluation of ground motion (PGV, Peak Ground Velocity) were taken from engineering regulations (standard value for perceptibility of vibrations, German DIN 4150 ). We developed a PSHA (probabilistic seismic hazard analysis) model for ground motion of induced seismicity. Thus, it is possible to specify the probability of exceedance of limiting values of PGV and to decide (e.g. by the regulator responsible for commissioning) whether the number of exceedances at these given limits are acceptable at a site or not. Additionally, hazard curves of induced and natural seismicity are compared to study the different impacts. Preliminary results which were derived using data from the operation phase of a plant, - for stiff soil, ignoring site effects - indicate higher frequencies of exceedance for induced seismicity than for natural seismicity only for low PGV values. The current work aims at refining our PSHA model by incorporating effects of local site conditions. They will be quantified using a concept of ambient seismic noise array measurements.