Microbial community and inorganic fluid analysis during CO2 storage within the frame of CO2SINK–Long-term experiments under in situ conditions

AbstractMicroorganisms play an important role in the transformation of material within the earth’s crust. The storage of CO2 could affect the composition of inorganic and organic components in the reservoir, consequently influencing microbial activities. To study the microbial induced processes together with geochemical, petrophysical and mineralogical changes, occurring during CO2 storage, long-term laboratory experiments under simulated reservoir P-T conditions were carried out. Clean inner core sections, obtained from the reservoir region at the CO2 storage site in Ketzin (Germany) from a depth of about 650 m, were incubated in high pressure vessels together with sterile synthetic formation brine under in situ P-T conditions of 5.5 MPa and 40 °C. A 16S rDNA based fingerprinting method was used to identify the dominant species in DNA extracts of pristine sandstone samples. Members of the α- and β-subdivisions of Proteobacteria and the Actinobacteria were identified. So far sequences belonging to facultative anaerobic, chemoheterotrophic bacteria (Burkholderia fungorum, Agrobacterium tumefaciens) gaining their energy from the oxidation of organic molecules and a genus also capable of chemolithoautotrophic growth (Hydrogenophaga) was identified.During CO2 incubation minor changes in the microbial community composition were observed. The majority of microbes were able to adapt to the changed conditions. During CO2 exposure increased concentrations of Ca2+, K+, Mg2+ and SO42− were observed. Partially, concentration rises are (i) due to equilibration between rock pore water and synthetic brine, and (ii) between rock and brine, and are thus independent on CO2 exposure. However, observed concentrations of Ca2+, K+, Mg2+ are even higher than in the original reservoir fluid and therefore indicate mineral dissolution due to CO2 exposure

Monitoring of the microbial community composition in deep subsurface saline aquifers during CO2 storage in Ketzin, Germany

AbstractThis study characterized the composition and activity of the autochthonous microbial community in formation fluids of a saline CO2 storage aquifer during CO2 injection and during an N2 lift. The clean-up of the wells prior CO2 injection by N2 lift decreased the total microbial cell numbers, and the number of sulphate reducing bacteria (SRB) was reduced by at least two orders of magnitude. Fluorescence in situ Hybridisation (FISH) and molecular fingerprinting demonstrated that the microbial community was strongly influenced by the CO2 injection. Before CO2 arrival, up to 106 cells ml-1 were detected by DAPI-staining at a depth of 647 m below the surface. The microbial community was dominated by fermentative halophilic bacteria and sulphate reducing bacteria. Both the FISH and fingerprinting analyses revealed quantitative and qualitative changes after CO2 arrival. An enhanced activity and quantity of the microbial population after five months of CO2 storage indicated that the community was able to adapt to the extreme conditions of the deep biosphere and to the extreme changes of these anthropogenically modified conditions

Mobilisation of organic compounds from reservoir rocks through the injection of CO₂ - comparison of baseline characterization and laboratory experiments

In the framework of CO₂ storage activities, the aim of our investigations is mainly to evaluate the effects of supercritical CO₂ (scCO₂) on the quantitative and qualitative extraction of organic compounds from reservoir rocks. Within the scope of the CO₂ storage project CO₂SINK the major task was to identify key mechanisms occurring in the reservoir as a result of the injection of CO₂ into a saline aquifer. Here, it is of special interest what types and amounts of organic matter will be extracted and mobilized from the reservoir rocks in conjunction with the injection of scCO₂. Thus, our investigations may help to evaluate the efficiency and reliability of the long-term storage of CO₂ in such a geological system. Here, we present compound-specific results from laboratory scCO₂-extraction experiments on reservoir rock samples from the CO₂ storage site in Ketzin, Germany. Low molecular weight organic acids (LMWOA) as well as polar lipid fatty acids (PLFA) extracted by scCO2 were analysed using ion chromatography and gas chromatography-mass spectrometry, respectively. Through the exposure to scCO₂ mainly formate and acetate, but also other LMWOA were released from the rock samples in varying amounts. PLFA profiles of scCO₂ extracts were dominated by saturated and unsaturated fatty acids with 16 and 18 carbon atoms of bacterial origin. The results of scCO₂ extraction are compared with the characterization of the organic inventory of pristine rock samples and fluid samples from observation wells of the Ketzin site to obtain information on quantitative and qualitative significance of the solvent potential of scCO₂

Comparison of the microbial community composition of pristine rock cores and technical influenced well fluids from the Ketzin pilot site for CO_{2} storage

Two geological formations at the CO_{2} storage pilot site in Ketzin (Germany) were geochemically and microbiologically characterized to further evaluate changes resulting from CO_{2} injection. Well fluids were collected from both Stuttgart (storage formation, ~650 m depth) and Exter Formations (~400 m depth, overlying the caprock) either through pump tests or downhole samplings. Rock samples were retrieved during a deep drilling into the Exter Formation and primarily comprised quartz, ferrous dolomite or ankerite, calcite, analcime, plagioclase and clay minerals, as determined through X-ray diffraction analyses. In the rocks, the total organic carbon (TOC), which potentially contributes to microbial growth, was mostly below 1000 mg kg^{-1}. The geochemical characterization of fluids revealed significant differences in the ionic composition between both formations. The microbial characterization was performed through fluorescence in situ hybridization and 16S rRNA gene fingerprinting. In the fluids obtained from the Stuttgart Formation, the microbial activity was affected by the relatively high TOC, introduced by the organic drill mud. The total cell counts were approximately 106 cells mL^{-1}. The microbial community was characteristic of a saline deep biosphere environment enriched through increased carbon availability, with sulfate-reducing bacteria as the most abundant microorganisms (up to 60 % of total cells). Species belonging to halophilic/halotolerant Proteobacteria and Firmicutes were primarily detected. In Exter Formation rocks, Proteobacteria and Actinobacteria were detected. These data provide an explicit reference to further evaluate environmental changes and community shifts in the reservoir during CO_{2} storage and provide information for evaluating the storage efficiency and reliability