Item

Abstract

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).