• Energy Research

AbstractAt Ketzin, located west of Berlin, the GFZ German Research Centre for Geosciences operates Europe's longest- running on-shore CO2 storage site. The Ketzin pilot site has been developed since 2004 and comprises three wells to depths of 750 m to 800 m and one shallow observation well, an injection facility and permanently installed monitoring devices. Since June 2008, CO2 is injected into 630 m to 650 m deep sandstone units (Upper Triassic Stuttgart Formation) in an anticlinal structure of the Northeast German Basin. Until mid of May 2012, about 61,400 t of CO2 have been stored safely. One of the most comprehensive monitoring concepts worldwide is applied and capable of detecting the behaviour of the CO2 in the subsurface. The Ketzin project demonstrates safe CO2 storage in a saline aquifer on a research scale and effective monitoring. This paper summarizes the key results obtained after four years of CO2 injection.

AbstractThe present study assesses potential geomechanical impacts of pore pressure increase induced by CO2 injection at a prospective CO2 storage site located in the Middle Bunter sequence in Eastern Germany. A 3D supraregional-scale structural geological model was implemented in one-way coupled hydro-mechanical simulations to assess caprock and fault integrity. Simulation results show a maximum ground uplift of 0.021 m at the end of CO2 injection, while shear failure observed at the simulated time steps does not achieve a significant density in the entire model. Consequently, reservoir, caprock and fault integrity are not compromised at any time of CO2 injection operation.

Deep un-mineable coal deposits are viable reservoirs for permanent and safe storage of carbon dioxide (CO2) due to their ability to adsorb large amounts of CO2 in the microporous coal structure. A reduced amount of CO2 released into the atmosphere contributes in turn to the mitigation of climate change. However, there are a number of geomechanical risks associated with the commercial-scale storage of CO2, such as potential fault or fracture reactivation, microseismic events, cap rock integrity or ground surface uplift. The present study assesses potential site-specific hydromechanical impacts for a coal deposit of the Upper Silesian Coal Basin by means of numerical simulations. For that purpose, a near-field model is developed to simulate the injection and migration of CO2, as well as the coal-CO2 interactions in the vicinity of horizontal wells along with the corresponding changes in permeability and stresses. The resulting effective stress changes are then integrated as boundary condition into a far-field numerical model to study the geomechanical response at site-scale. An extensive scenario analysis is carried out, consisting of 52 simulation runs, whereby the impacts of injection pressures, well arrangement within two target coal seams as well as the effect of different geological uncertainties (e.g., regional stress regime and rock properties) is examined for operational and post-operational scenarios. The injection-induced vertical displacements amount in maximum to 3.59 cm and 1.07 cm directly above the coal seam and at the ground surface, respectively. The results further demonstrate that neither fault slip nor dilation, as a potential consequence of slip, are to be expected during the investigated scenarios. Nevertheless, even if fault integrity is not compromised, dilation tendencies indicate that faults may be hydraulically conductive and could represent local pathways for upward fluid migration. Therefore, the site-specific stress regime has to be determined as accurately as possible by in-situ stress measurements, and also fault properties need to be accounted for an extensive risk assessment. The present study obtained a quantitative understanding of the geomechanical processes taking place at the operational and post-operational states, supporting the assessment and mitigation of environmental risks associated with CO2 storage in coal seams.

Abstract Pilot-scale CO 2 storage has been performed at the Ketzin pilot site in Germany from 2007 to 2013 with about 67 kt of CO 2 injected into the Upper Triassic Stuttgart Formation, focussing on efficient monitoring and long-term prediction strategies. We employed inverse modelling to revise the latest static geological reservoir model, considering bottomhole well pressures observed during hydraulic testing. Simulation results exhibit very good agreement with the observations, providing one reasonable permeability realization for the Ketzin pilot site near-well area. Furthermore, an existing hypothesis on the presence of a low-thickness sandstone channel between two wells is supported by our findings.

AbstractWe give an overview of the MUFITS reservoir simulator capabilities for modelling subsurface carbon dioxide storage using the EOS-modules GASSTORE and BLACKOIL. The GASSTORE module covers solid-liquid-gas flows of water, carbon dioxide and salt components, and includes an option for automatic generation of the BLACKOIL PVT tables. We test the simulator against several benchmarking studies and then consider an application case of CO2 storage at the Ketzin pilot site, Germany. The modelling results are in excellent agreement with those produced with common scientific and standard industrial simulators.

Underground coal gasification (UCG) converts coal to a high-calorific synthesis gas for the production of fuels or chemical feedstock. UCG reactors are generally operated below hydrostatic pressure to avoid leakage of UCG fluids into overburden aquifers. Additionally, fluid flow out of and into the reactor is also determined by the presence of the steam jacket, emerging in close reactor vicinity due to the high temperatures generated in UCG operation. Aiming at improving the understanding of the substantial role of the steam jacket in UCG operations, we employ numerical non-isothermal multiphase flow simulations to assess the occurring multiphase fluid flow processes. For that purpose, we first validate our modeling approach against published data on the U.S. UCG field trials at Hanna and Hoe Creek, achieving a very good agreement between our simulation and the observed water balances. Then, we discuss the effect of coal seam permeability and UCG reactor pressure on the dynamic multiphase flow processes in the reactor’s vicinity. The presented modeling approach allows for the quantification and prediction of time-dependent temperature and pressure distributions in the reactor vicinity, and thus steam jacket dynamics as well as reactor water in- and outflows.