Leonhard Ganzer

The impact of diagenetic fluid–rock reactions on Rotliegend sandstone composition and petrophysical properties (Altmark area, central Germany)

In the framework of the German R&D joint project CLEAN (CO2 large-scale enhanced gas recovery in the Altmark natural gas field), Rotliegend reservoir sandstones of the Altensalzwedel block in the Altmark area (Saxony-Anhalt, central Germany) have been studied to characterise litho- and diagenetic facies, mineral content, geochemical composition, and petrophysical properties. These sands have been deposited in a playa environment dominated by aeolian dunes, dry to wet sand flats and fluvial channel fills. The sediments exhibit distinct mineralogical, geochemical, and petrophysical features related to litho- and diagenetic facies types. In sandstones of the damp to wet sandflats, their pristine red colours are preserved and porosity and permeability are only low. Rocks of the aeolian environment and most of the channel fill deposits are preferentially bleached and exhibit moderate to high porosity and permeability. Although geochemical element whole rock content in these rocks is very similar, element correlations are different. Variations in porosity and permeability are mainly due to calcite and anhydrite dissolution and differences in clay coatings with Fe-bearing illitic-chloritic composition exposed to the pore space. Moreover, mineral dissolution patterns as well as compositions (of clays and carbonate) and morphotypes of authigenic minerals (chlorite, illite) are different in red and bleached rocks. Comparison of the geochemical composition and mineralogical features of diagenetically altered sandstones and samples exposed to CO2-bearing fluids in laboratory batch experiments exhibit similar character. Experiments prove an increase in wettability and water binding capacity during CO2 impact.

An Efficient Algebraic Multigrid Solver Strategy for Adaptive Implicit Methods in Oil Reservoir Simulation

We propose a new, efficient, adaptive algebraic multigrid (AMG) solver strategy for the discrete systems of partial differential equations arising from structured or unstructured grid models in reservoir simulation. The proposed strategy has been particularly tailored to linear systems of equations arising in adaptive implicit methods. The coarsening process of the AMG method designed automatically employs information on the physical structure of the models; as a smoother, an adaptive ILUT method is employed, taking care of an efficient solution of the hyperbolic parts whilst providing adequately smooth errors for the elliptic parts. To achieve a good compromise of high efficiency and robustness for a variety of problem classes – ranging from simple, small black-oil to challenging, large compositional models – an automatic, adaptive ILUT parameter and AMG solver switching strategy, α-SAMG, has been developed. Its efficiency is demonstrated for eight industrial benchmark cases by comparison against standard one-level and AMG solvers as well as the pure onelevel variant of the proposed new strategy. In addition, very promising results of first parallel runs are shown.

Influence of added hydrogen on underground gas storage: a review of key issues

The existing infrastructure of the natural gas transportation pipeline network and underground gas storage (UGS) facilities in Germany provides an opportunity and huge capacity to feed, transport and store hydrogen and synthetic fuel gases containing hydrogen, produced from renewable sources. At low hydrogen concentrations, only minor changes to gas transportation equipment will be required. In contrast, the UGS designed in converted gas fields and aquifers are particularly susceptible to the effect of hydrogen. Due to a lack of adequate knowledge about the hydrogen concentration in natural gas, which can be tolerated by the downhole equipment, reservoir and caprocks, the injection of natural gas containing hydrogen in the existing porous UGS is strongly limited. Key issues addressed in this paper are the change in capacity and efficiency of UGS associated with the blending of hydrogen in the stored natural gas, the geological integrity of the reservoir and caprocks, the technical integrity of gas storage wells, durability of the materials used for well completions, corrosion and environmental risks associated with the products of microbial metabolism.

The chemical dissolution and physical migration of minerals induced during CO2 laboratory experiments: their relevance for reservoir quality

The characterization of the quality and storage capacity of geological underground reservoirs is one of the most important and challenging tasks for the realization of carbon capture and storage (CCS) projects. One approach for such an evaluation is the upscaling of data sets achieved by laboratory CO2 batch experiments to field scale. (Sub)-microscopic, petrophysical, tomographic, and chemical analytical methods were applied to reservoir sandstone samples from the Altmark gas field before and after static autoclave batch experiments at reservoir-specific conditions to study the relevance of injected CO2 on reservoir quality. These investigations confirmed that the chemical dissolution of pore-filling mineral phases (carbonate, anhydrite), associated with an increased exposure of clay mineral surfaces and the physical detachment and mobilization of such clay fines (illite, chlorite) are most appropriate to modify the quality of storage sites. Thereby the complex interplay of both processes will affect the porosity and permeability in opposite ways—mineral dissolution will enhance the rock porosity (and permeability), but fine migration can deteriorate the permeability. These reactions are realized down to ~µm scale and will affect the fluid–rock reactivity of the reservoirs, their injectivity and recovery rates during CO2 storage operations.

Self-organization and shock waves in underground methanation reactors and hydrogen storages

Abstract We consider coupled hydrodynamic and biochemical phenomena that occur in an underground porous reservoir, in which a mixture of hydrogen with other gases has been injected. The presence of methanogenic bacteria in geological strata initiates the natural underground methanation, i.e., the conversion of the mixture of H

Mathematical modeling of unstable transport in underground hydrogen storage

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Evaluation of Geo-processes

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