Description: Due to the strong interest in geochemical CO2-fluid-rock interaction in the context of geological storage of CO2 a growing number of research groups have used a variety of different experimental ways to identify important geochemical dissolution or precipitation reactions and – if possible – quantify the rates and extent of mineral or rock alteration. In this inter-laboratory comparison the gas-fluid-mineral reactions of three samples of rock-forming minerals have been investigated by 11 experimental labs. The reported results point to robust identification of the major processes in the experiments by most groups. The dissolution rates derived from the changes in composition of the aqueous phase are consistent overall, but the variation could be reduced by using similar corrections for changing parameters in the reaction cells over time. The comparison of experimental setups and procedures as well as of data corrections identified potential improvements for future gas-fluid-rock studies.

Description: The sequestration of CO2 gas streams of different origins into e.g. deep saline aquifers opened a major area for geochemical research on gas-fluid-rock interaction at elevated in situ pressures and temperatures. Besides the inherent problems of experimental approaches to constrain the kinetic parameters of the slow dissolution processes of silicates in highly saline brines, the often conincident dissolution and precipitation reactions hamper the determination of precise dissolution or precipitation rates in more complex experimentat approaches, e. g flow through experiments. To facilitate the precise determination of the amount of dissolved ions incorporated into newly formed precipitates within the reaction chambers, a spatial analyses of incorporation of isotopically- labelled elements/ions (e.g. 18 O) into mineral precipitates is beeing developed by using high resolution ToF-SIMS techniques. With this technique it is possible to simultaneously image the elemental, isotopic, and molecular composition in rocks with high spatial resolution. Also, the elemental and isotopical distribution as a function of depth can be monitored. To set up a database of a variety of rock-forming minerals, ToF-SIMS spectra were recorded in different measurement modes - either on individual crystal grains of less than 500 μm diameter or in thin sections from rocks envisaged as potential storage formations in Germany. Furthermore, a calibration of the isotopic scale has been performed by measuring artificially prepared minerals with different percentages of isotope labels incorporated. Thereby, the distinction of the incorporation of ions from dissolution (e.g. 99% 16 O) in contrast to those from the synthetic brine (e.g. 99% 18 O) is possible. In addition, using e.g. 18 O labels as atomic oxygen ions, the isotopic composition in larger molecules such as CO3 could be used to unambigously identify the mineral, into the labeled oxygen has been incorporated (e.g. clay minerals or carbonates).

Description: Due to the strong interest in geochemical CO2-fluid-rock interaction in the context of geological storage of CO2 a growing number of research groups have used a variety of different experimental ways to identify important geochemical dissolution or precipitation reactions and – if possible – quantify the rates and extent of mineral or rock alteration. In this inter-laboratory comparison the gas-fluid-mineral reactions of three samples of rock-forming minerals have been investigated by 11 experimental labs. The reported results point to robust identification of the major processes in the experiments by most groups. The dissolution rates derived from the changes in composition of the aqueous phase are consistent overall, but the variation could be reduced by using similar corrections for changing parameters in the reaction cells over time. The comparison of experimental setups and procedures as well as of data corrections identified potential improvements for future gas-fluid-rock studies.

Description: Carbon dioxide capture and geological storage (CCS) is being developed to reduce the carbon dioxide (CO2) emissions from anthropogenic point sources, e.g. fossil-fuel power plants, to the atmosphere. To establish CCS technology, it is indispensable to develop a reliable database and geochemical models concerning the geological storage of CO2, e.g. in saline aquifers, which are to be filled with “overwhelmingly CO2” (Directive 2009/31/EC). To establish reliable models it is essential to have applicable thermodynamic properties, kinetic data, and a good understanding of the occurring chemical reactions. So far most experiments and existing data apply to pure CO2 gas instead of the captured CO2 waste gas that will contain minor amounts of co-captured gases, e.g. O2, N2, NOx, SOx, CO, H2, H2S. Quantitative measures of the chemical alterations due to these accessory gases are scarce. In the national COORAL project “ CO2 Purity for Separation and Storage”, a number of institutions work towards a better understanding of environmentally and economically feasible concentrations of the accessory gases during capture, transport, injection and storage. The sub-project at BGR focuses on high-pressure and high-temperature (HPHT) experiments to elucidate mineral and fluid alterations and quantify kinetic rates for the mineral-fluid- CO2-co-injected gas system. An unstirred batch-reactor system allows for four contemporaneous experiments at precisely defined p-T conditions of up to p≤590 bar T≤350 °C. Runs are conducted using three components: (1) natural mono-minerals, (2) salt solutions representing brines of deep saline aquifers in Northern Germany and (3) binary gas mixtures of CO2 plus one accessory gas. All experiments take place in an inert environment, using gold reaction cells with volumes of up to 130 ml, which allow the addition or removal of fluids throughout the experiment without altering the experimental conditions. Further experiments comprise experiments using (1) multi-mineral set-ups in a batch experiment and (2) up to 45-cm-long sedimentary rock cores in flow-through reactors. The latter system is currently under construction, while batch - and capsular - experiments run successfully. To further optimize the experimental design and to evaluate the experiments the project combines laboratory experiments and numerical simulations, applying the geochemical simulators PHREEQC and ChemApp which will be coupled to OpenGeoSys (OGS) for thermo-hydro-mechanical-chemical (THMC) process simulations.

Description: In the research activities on geological storage of carbon dioxide many studies mainly focus on the impact of pure CO2 gas on the storage formations. However, flue gas streams of power plants not only contain CO2, but also number of trace gases such as O2, N2, Ar, NOX, SOX, CO, H2, H2S, COS and CH4. These trace gases may not only interact with pipeline material, but can also trigger short-term and long-term changes within the subsurface storage lithology. The chemical reactivity of each of these compounds has to be evaluated and their interactions with each other have to be understood, especially since some of them are far more reactive than CO2. Within the project COORAL (= CO2 Purity for Capture and Storage) we concentrate on geochemical investigations to determine reaction pathways and kinetics of different mineral phases typical for potential German storage formations as influenced by the presence of trace gases within the flue gas stream. Quantitative measurements of these reactions are relatively well described for pure CO2 systems but are so far not well described for multi-component mixtures. We combine laboratory experiments (batch and flow-through) with numerical simulations applying the geochemical simulators PHREEQC and ChemApp, which will be coupled to GeoSys/RockFlow for coupled thermo-hydro-mechanical-chemical (THMC) process simulations. Calculations and experiments are performed for temperatures up to 200°C and pressures up to 50 MPa. The aim of the study is to determine optimal maximum concentration levels of trace gases in flue gas streams to be used in geological CO2 storage.

Description: To establish reliable numerical models that depict the geochemical processes caused by the storage of CO2 in saline aquifers it is essential to have an applicable database. This has to include thermodynamic properties and kinetic data of those gas mixtures occurring in the captured CO2 gas stream, which will contain minor amounts of gases such as O2, N2, NO x , SO x, CO, H2 S. However, quantitative measures of the chemical alterations due to these accessory gases are scarce at relevant conditions. The COORAL project “CO2 Purity for Capture and Storage”, concentrates on the effects of accessory gases during all four processes: capture, transport, injection and storage. At BGR it is the storage that is in focus. High-pressure-high-temperature (HPHT) experiments are carried out using unstirred batch- reactor systems (P & 590 bar; T & 350°C) to elucidate mineral and fluid alterations and quantify kinetic rates for different mineral–fluid–CO2–co-injected gas system. A first set of experiments using pure CO2 and carbonates allowed testing the laboratory set-up and adjusting the modelling environment (PHREEQC). Dolomite-brine-CO2 experiments exhibited a very good reproducibility of the increase in cation concentrations at the different stages of the experiment. Release rates for both, Mg and Ca, vary between 2*10-10 mol s-1 cm - 2 at the very beginning and 4*10-13 mol s-1 cm -2 just before approaching steady state. There is a tendency towards slightly higher rates for Ca release during the first stage of the experiment. The main target of the running experiments is set on the effects of binary gas mixtures in the system mineral–fluid–CO2–O2 (this contribution) and mineral–fluid–CO2–SO2 [1]. The mineral phase consists of carefully crushed, sorted and cleaned natural mono-minerals while the natural saline water is represented by a Na-Cl solution of 150 g/l NaCl in most cases.