Abstract: Conventionally produced and transported natural gas is commonly free of hydrogen. However, gases produced from renewable energy sources and fed to natural gas transportation networks can contain hydrogen. The objective of this study is to summarize available knowledge on the behavior of gases containing hydrogen from the assessed published literature with special focus on the issue of underground gas storage. This report outlines the aspects related to the technical and geological integrity of the underground reservoir and cavern gas, and reflects on issues and solutions for the underground storage of natural gas with added hydrogen. The issues related to the influence of added hydrogen on the capacity and energy efficiency of such underground gas storages in Germany, and the safety aspects are also outlined. It can be conclusively stated that in particular cases the down hole equipment of the underground storage of natural gas with added hydrogen should be adapted to the new hydrogenous environment. Here, the high hydrogen diffusivity poses a risk of hydrogen-induced corrosion and imposes special requirements on the materials used. The hydrodynamic behavior of storage and the sealing ability of cap rock could also be altered because of the effect of the hydrogen present. In addition microbiological activity provides a particular risk. Most of the issues indicated in this report are insufficiently studied. Therefore more detailed research on the technical and geological issues of the underground storage of natural gas with added hydrogen is recommended. Kurzfassung: Im Regelfall ist produziertes Erdgas und das im Hochdruck(HD)-Transportnetz vorliegende Gas wasserstofffrei. Durch Einspeisung von regenerativ erzeugten Gasen können dem HD-Transportnetz jedoch Gase mit höherer Wasserstoffkonzentration zugeführt werden. Ziel dieser Studie ist es, vorhandene Erkenntnisse zum Verhalten des wasserstoffhaltigen Erd-gases in Untertagespeichern aus der Literatur zusammenzutragen und aufzubereiten. Dieser Bericht stellt Aspekte der technischen und geologischen Dichtheit von Poren- und Kavernenspeichern bezüglich der Untertagespeicherung von Gas mit Wasserstoff als Be-gleitkomponente dar und beleuchtet mögliche Fragestellungen wie auch potentielle Lösungen. Des Weiteren wird der Einfluss auf die Kapazität und Effizienz solcher Speicher in Deutschland betrachtet sowie auf Sicherheitsaspekte eingegangen. Zusammenfassend kann gesagt werden, dass das Untertageequipment an die Speicherung von wasserstoffhaltigem Erdgas gegebenenfalls angepasst werden muss. Die hohe Diffusion von Wasserstoff und das durch Wasserstoff induzierte Korrosionsrisiko stellen besondere Anforderungen an das eingesetzte Material. In Bezug auf die Speicherlagerstätte könnte sich die Wirksamkeit der Abdichtung durch das Deckgebirge und das hydrodynamische Verhalten des Speichers ändern. Zusätzlich besteht die Gefahr einer gesteigerten mikrobiologischen Aktivität. Die meisten in diesem Bericht angesprochenen Aspekte sind jedoch noch nicht ausreichend untersucht worden, weshalb eine besondere Untersuchung der technischen und geologischen Bedingungen empfohlen wird.

This report covers the results obtained during the second phase of the research project DGMK 746/2 titled “Experimental and Numerical Analysis of Polymer Flooding Processes using Micromodels”. The overall project aims to provide new insights into two-phase displacement processes - in particular polymer EOR processes - using micro visual studies supported by advanced micro models („chips"). The main targets for the second project phase were defined based on several challenges encountered during the first project phase, such as (a) the extension of the laboratory setup to enable flooding experiments at typical reservoir temperature conditions, (b) the design and creation of new advanced micro models based on micro-CT images with specified wetting conditions, (c) the validation of the micro model flooding results by comparison with core flooding as well as (d) a further extension of the polymer rheological database. An improved microfluidics setup with heating capabilities was successfully realized during the project phase, which enabled suitable experimental conditions matching the typical reservoir oil temperatures observed in German oil fields. Also, a core-flooding setup was created at the department which enabled the performance of core-plug experiments at equivalent flooding conditions. For the generation of advanced micro models, micro-CT images were obtained from Bentheimer core plugs, and a workflow was created that aims to convert the 3D flow paths of the real rock to the pseudo-2D flow patterns obtainable in the sandwich micro-models generated in this research project. Instead of a quarter of a 5-spot pattern, these new chips were using a linear flow pattern mimicking the core-plug flooding geometry. The wettability of the micro models was successfully modified using chemicals. The comparison of flooding results from micro models and the core plug is documented in the project report, as well as the numerical simulation of the chips and the core plug experiment. The rheological database was extended by various HPAM and xanthan polymers. Particular focus was given to viscoelastic properties and the visualization of stream lines during the polymer flow through the chips.

DGMK-Report concerning "Production and Reservoir Engineering"

The focus of this R&D project is the development of a new integrated workflow using state of the art optimization techniques combined with the adjoint method for history matching. The integration concept is aimed at developing a robust workflow supporting decision processes for evaluating alternative production scenarios of oil and gas fields. For this purpose, SenEx, which is an advanced sensitivity computation tool capable of modifying rock properties on grid-block level, has been linked to the existing optimization framework MEPO. The Hotlink thus developed has been tested, reviewed and enhanced. Within the framework of this re-search project, the developed workflows have been applied to a spectrum of history match-ing problems with varying complexities. In general, multiple geological realizations were used to capture existing uncertainty in an extended optimization workflow, including history matching and production optimization. Us-ing this method, history match is typically achieved with significantly less number of iterations compared to existing methods. The workflow applied is useful for evaluating alternative re-development scenarios, quantifying uncertainties and generating realistic history matched models. Benchmarking work performed provided better insights into benefits and limitations of the adjoint method.