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

Process recovery after CaO addition due to granule formation in a CSTR Co-Digester : a tool to influence the composition of the microbial community and stabilize the process?

The composition, structure and function of granules formed during process recovery with calcium oxide in a laboratory-scale fermenter fed with sewage sludge and rapeseed oil were studied. In the course of over-acidification and successful process recovery, only minor changes were observed in the bacterial community of the digestate, while granules appeared during recovery. Fluorescence microscopic analysis of the granules showed a close spatial relationship between calcium and oil and/or long chain fatty acids. This finding further substantiated the hypothesis that calcium precipitated with carbon of organic origin and reduced the negative effects of overloading with oil. Furthermore, the enrichment of phosphate minerals in the granules was shown, and molecular biological analyses detected polyphosphate-accumulating organisms as well as methanogenic archaea in the core. Organisms related to Methanoculleus receptaculi were detected in the inner zones of a granule, whereas they were present in the digestate only after process recovery. This finding indicated more favorable microhabitats inside the granules that supported process recovery. Thus, the granule formation triggered by calcium oxide addition served as a tool to influence the composition of the microbial community and to stabilize the process after overloading with oil

Effects of heat shocks on biofilm formation and the influence on corrosion and scaling in a geothermal plant in the North German Basin

At geothermal plants, process failures often occur due to corrosion and scaling processes. Especially after heat extraction, sulfate reducing bacteria contribute to corrosion processes by producing reduced sulfur compounds. In biofilms containing scales such as iron sulfides, corrosion processes are enhanced. In a mobile bypass system located at the geothermal plant in Neubrandenburg (North German Basin), the influence of biofilm formation on corrosion and scaling was investigated. Short-term heat shocks were successfully tested in the bypass system in order to reduce biofilm formation and thus to diminish corrosion and scaling processes

Influence of microbial processes on the operational reliability in a geothermal heat store : results of long-term monitoring at a full scale plant and first studies in a bypass system

This paper describes microbial metabolic processes that are considered to be relevant for the technical reliability of a geothermal heat store. The study reports on changes of the microbial community composition in geothermal well fluids of different temperatures and after plant downtimes monitored by genetic fingerprinting. Stagnant conditions favored the enrichment of bacteria, sulfate reducers (SRB), and sulfur oxidizers (SOB) in the well. Furthermore higher concentrations of DOC, SO_4_2-, H_2S, and H_2 were detected in the first fluids produced after plant downtime. The increased abundance of SOB indicated oxygen ingress during plant downtime. The interaction of SRB and SOB might have further enhanced corrosion and scaling processes. A mobile bypass system installed at the site will help to understand the processes occurring in the well and to study biofilm formation and corrosion rates at different temperatures

Mineralogical and geochemical analysis of Fe-phases in drill-cores from the Triassic Stuttgart Formation at Ketzin CO₂ storage site before CO₂ arrival

Reactive iron (Fe) oxides and sheet silicate-bound Fe in reservoir rocks may affect the subsurface storage of CO2 through several processes by changing the capacity to buffer the acidification by CO2 and the permeability of the reservoir rock: (1) the reduction of three-valent Fe in anoxic environments can lead to an increase in pH, (2) under sulphidic conditions, Fe may drive sulphur cycling and lead to the formation of pyrite, and (3) the leaching of Fe from sheet silicates may affect silicate diagenesis. In order to evaluate the importance of Fe-reduction on the CO2 reservoir, we analysed the Fe geochemistry in drill-cores from the Triassic Stuttgart Formation (Schilfsandstein) recovered from the monitoring well at the CO2 test injection site near Ketzin, Germany. The reservoir rock is a porous, poorly to moderately cohesive fluvial sandstone containing up to 2–4 wt% reactive Fe. Based on a sequential extraction, most Fe falls into the dithionite-extractable Fe-fraction and Fe bound to sheet silicates, whereby some Fe in the dithionite-extractable Fe-fraction may have been leached from illite and smectite. Illite and smectite were detected in core samples by X-ray diffraction and confirmed as the main Fe-containing mineral phases by X-ray absorption spectroscopy. Chlorite is also present, but likely does not contribute much to the high amount of Fe in the silicate-bound fraction. The organic carbon content of the reservoir rock is extremely low (<0.3 wt%), thus likely limiting microbial Fe-reduction or sulphate reduction despite relatively high concentrations of reactive Fe-mineral phases in the reservoir rock and sulphate in the reservoir fluid. Both processes could, however, be fuelled by organic matter that is mobilized by the flow of supercritical CO2 or introduced with the drilling fluid. Over long time periods, a potential way of liberating additional reactive Fe could occur through weathering of silicates due to acidification by CO2

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

Influence of drill mud on the microbial communities of sandstone rocks and well fluids at the Ketzin pilot site for CO_{2} storage

At a pilot site for CO_{2} storage in Ketzin (Germany), a drastic decrease in injectivity occurred in a well intended for injection. This was attributed to an obstruction of the pore throats due to microbial degradation of the organic drill mud and subsequent iron sulfide (FeS) precipitation in the highly saline brine (240 g L^{-1}). To better understand the biogeochemical processes, the response of the autochthonous microbial community to drill mud exposure was investigated. Pristine cores of two aquifers with different salinity were incubated under simulated in situ conditions (50 bar, 40 ^{\circ}C and 45 bar, 25 ^{\circ}C, respectively) and CO_{2} atmosphere. For the first time, rock cores obtained from the CO_{2} plume of the storage formation were investigated. The influence of acetate as a biodegradation product of drill mud polymers and the effectiveness of a biocide were additionally tested. Increased microbial diversities were observed in all long-term (8-20 weeks) incubations, even including biocide. Biofilm-like structures and small round-shaped minerals of probable microbiological origin were found. The results indicate that the microbial community remains viable after long-term CO_{2} exposure. Microorganisms hydrolyzing cellulose polymers (e.g., Burkholderia spp., Variovorax spp.) biodegraded organic components of the drill mud and most likely produced low molecular weight acids. Although the effects of drill mud were less strong as observed in situ, it was demonstrated that acetate supports the growth of sulfate-reducing bacteria (i.e., Desulfotomaculum spp.). The microbial-induced precipitation of amorphous FeS reduced the injectivity in the near-well area. Therefore, when using organic drill mud, the well must be cleaned intensively to minimize the hazards of bacterial stimulation

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