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Gypsum crystals are found at the well perforation of observation well Ktzi 202 of the test site for CO2 storage at Ketzin, Germany. XRD analysis confirms pure gypsum. Fluid samples before and after CO2 injection are analyzed. Geochemical modeling is conducted to identify the mechanisms that lead to gypsum formation. The modeling is carried out with PHREEQC and Pitzer database due to the high salinity of up to 5 mol per kg water. Due to their significantly higher reactivity compared to other minerals like silicates, calcite, dolomite, magnesite, gypsum, anhydrite, and halite are considered as primary mineral phases for matching the observed brine compositions in our simulations. Calcite, dolomite, and gypsum are close to saturation before and after CO2 injection. Dolomite shows the highest reactivity and mainly contributes to buffering the brine pH that initially decreased due to CO2 injection. The contribution of calcite to the pH-buffering is only minor. Gypsum and anhydrite are no geochemically active minerals before injection. After CO2 injection, gypsum precipitation may occur by two mechanisms: (i) dissociation of CO2 decreases activity of water and, therefore, increases the saturation of all minerals and (ii) dolomite dissolution due to pH-buffering releases Ca2+ ions into solution and shifts the mass action to gypsum. Gypsum precipitation decreases with increasing temperature but increases with increasing partial CO2 pressure. Our calculations show that calcium sulfate precipitation increases by a factor of 5 to a depth of 2000 m when Ketzin pressure and temperature are extrapolated. In general, gypsum precipitation constitutes a potential clogging hazard during CO2 storage and could negatively impact safe site operation. In the presented Ketzin example, this threat is only minor since the total amount of gypsum precipitation is relatively small. [ABSTRACT FROM AUTHOR]

Germany 2050: For the first time Germany reached a balance between its sources of anthropogenic CO2 to the atmosphere and newly created anthropogenic sinks. This backcasting study presents a fictional future in which this goal was achieved by avoiding (∼645 Mt CO2), reducing (∼50 Mt CO2) and removing (∼60 Mt CO2) carbon emissions. This meant substantial transformation of the energy system, increasing energy efficiency, sector coupling, and electrification, energy storage solutions including synthetic energy carriers, sector‐specific solutions for industry, transport, and agriculture, as well as natural‐sink enhancement and technological carbon dioxide options. All of the above was necessary to achieve a net‐zero CO2 system for Germany by 2050. Plain Language Summary: Here a net‐zero‐2050 Germany is envisioned by combining analysis from an energy‐system model with insights into approaches that allow for a higher carbon circularity in the German system, and first results from assessments of national carbon dioxide removal potentials. A back‐casting perspective is applied on how net‐zero Germany could look like in 2050. We are looking back from 2050, and analyzing how Germany for the first time reached a balance between its sources of CO2 to the atmosphere and the anthropogenic sinks created. This would consider full decarbonization in the entire energy sector and being entirely emission‐free by 2050 within three priorities identified as being the most useful strategies for achieving net‐zero: (a) Avoiding‐ (b) Reducing‐ (c) Removing emissions. This work is a collaboration of interdisciplinary scientists with the Net‐Zero‐2050 cluster of the Helmholtz Climate Initiative HI‐CAM. Key Points: The net‐zero system shows that for countries like Germany, avoiding CO2 emissions was the largest contribution to achieve net‐zero CO2With the three strategies of emissions avoidance, reduction, and removal, Germany has achieved its net‐zero CO2 goal for the first timeIn addition, to natural sink enhancement carbon dioxide removal (CDR) options, technological CDR measures combined with geological CO2 storage were necessary to reach net‐zero CO2 [ABSTRACT FROM AUTHOR]

Highlights: [•] Operational monitoring ensures safe injection operation at Ketzin pilot site. [•] Downhole P–T measurements are recommended for CO2 storage sites. [•] DTS safety monitoring improves operational processes. [•] CO2 storage in on-shore deep saline formations can be realized. [Copyright &y& Elsevier]

Surface-downhole electrical resistivity tomography (SD-ERT) surveys were repeatedly carried out to image CO2 injected at the pilot storage Ketzin, Germany. The experimental setup combines surface with downhole measurements by using a permanent electrode array that has been deployed in three wells. Two baseline experiments were performed during the site startup and three repeat experiments were performed during the first year of CO2 injection. By the time of the third repeat, approximately 13,500 tons of CO2 had been injected into the reservoir sandstones at about 650 m depth. Field data and inverted resistivity models showed a resistivity increase over time at the CO2 injector. The lateral extent of the related resistivity signature indicated a preferential CO2 migration toward the northwest. Using an experimental resistivity-saturation relationship, we mapped CO2 saturations by means of the resistivity index method. For the latest repeat, CO2 saturations show values of up to 70% near the injection well, which matches well with CO2 saturations determined from pulsed neutron-gamma logging. The presence of environmental noise, reservoir heterogeneities, and irregularities in the well completions are the main sources of uncertainty for the interpretations. The degradation of the permanently installed downhole components is monitored by means of frequently performed resistance checks. In consistency with the SD-ERT data, these resistance checks indicate a long-term resistivity increase near the CO2 injector. In conclusion, the investigations demonstrate the capability of surface-downhole electrical resistivity tomography to image geologically stored CO2 at the Ketzin site. [ABSTRACT FROM AUTHOR]

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Abstract: The major task of a safety surveillance concept is to support the closed loop of reservoir management, i.e. to guarantee an iterative interaction between reservoir monitoring and numerical simulation. The presented research is based on the experience gained on the permanent geoelectrical monitoring at the Ketzin CO2 pilot storage site continuously operating since 2007. We have structured this experience in a modular monitoring workflow which offers well prepared links to actual process data, petrophysical data, and reservoir simulation. First results have been reached in major topics such as site-specific customization of technical tools, data acquisition and processing, and data evaluation. Structuring this approach in a modular manner allows the geoelectric monitoring at the Ketzin site to be efficiently scaled up and adapted to the fit-for-purpose requirements of future CCS demonstrations. [Copyright &y& Elsevier]

Abstract: This reservoir geomechanical study assesses the impact on top and fault seals integrity of fluid pressure changes associated with carbon dioxide (CO2) storage in a saline formation. The case studied is the CO2SINK experiment at in Ketzin, Germany, where up to 60 ktons of CO2 are being injected. Injection commenced in June 2008. A 3-dimensional (3D) geomechanical model of the site is built through integrated analyses of geologic, seismic, logging, drilling, and laboratory test data. First, the grid is expanded from a reservoir model up to surface, down to basement and laterally by about 3 times the pressure perturbation dimensions, while honouring all available structural, stratigraphic and lithological data. The grid cells are populated with density, poroelastic and strength properties upscaled from a 1-dimensional (1D) mechanical model built and validated along the Ktzi 201/2007 CO2 injector well. Cells cut by faults are considered an equivalent medium representative of a jointed rock mass. The 3D geomechanical model is then dynamically linked to the reservoir model. Static equilibrium prior to injection is achieved by applying initial fluid pressure and gravity loads, as well as stress boundary conditions chosen so as to match in situ stress measurements. Stress path and rock deformation associated with CO2 injection are then simulated. Pressure change data is passed from the flow simulator to the geomechanical simulator at selected time steps. Calculated stress path and strains are then used to investigate the possible occurrence and location of caprock failure and fault reactivation. Other results, such as ground surface elevation changes and sources of uncertainties are also highlighted. No failure is observed in the caprock and faults remain stable during CO2 injection operations. Limited vertical displacement (maximum 5 mm) is predicted at surface. [Copyright &y& Elsevier]

Abstract: At the CO2 storage site Ketzin, near Berlin (Germany), an integrated monitoring concept has been applied for characterization of the reservoir state before and during CO2 injection. Electrical Resistivity Tomography (ERT) is an essential part of this multi-method concept in order to image the spatial extent of the CO2 plume. ERT is shown to be sensitive to saturation changes caused by propagation of supercritical CO2 within a brine-filled reservoir. A permanent downhole electrode installation is placed behind casing in the three Ketzin wells (one for CO2 injection and two for observation). The so-called Vertical Electrical Resistivity Array (VERA) is deployed as crosshole configuration at a depth ranging from 590 to 735 meters, penetrating the Stuttgart formation, which hosts the target storage reservoir. For more than two years after finishing drilling and installation work the electrode array has been operating at a temperature of about 35 °C, an average reservoir pressure of about 75 bar, and a formation fluid pH of 5.5. These conditions have an effect on the life time of the components of the electrical monitoring system. Therefore, the performance of the VERA system has to be evaluated thoroughly during its long-term application. From the first results of the ongoing project we can conclude that crosshole ERT is indeed valuable as part of the CO2 monitoring program. Further use of the time-lapse resistivity data is in progress, e.g. support of CO2 distribution mapping in conjunction with results of seismic measurements. In the frame of an integrated monitoring concept, crosshole ERT can support the regulator’s work concerning safe reservoir operation and efficient risk management. [Copyright &y& Elsevier]