Long-term underground storage of hydrogen
In the H2STORE project, scientists established that hydrogen can induce rock alterations under specific conditions. However, the gas can also cause alterations to other materials, such as steel alloys. Therefore, in the HyINTEGER follow-up project, the researchers are now investigating the interaction between the technical and natural reservoir components. This should help to enable the longer-term storage of energy.
|Project status||Laboratory experiments for evaluation purposes|
|Project duration||January 2016 until December 2018|
The HyINTEGER project is based on the results of the previous H2STORE project. This project investigated the influence of hydrogen storage on rocks in potential pore reservoirs (sandstone horizons) in geological substrata. This work showed that hydrogen can induce rock alterations under specific conditions. It may also possibly alter other materials such as steel, well cements and elastomeric seals. The researchers in the HyINTEGER project are therefore investigating the interaction between the technical and natural reservoir components (rocks and pore fluids) under pressure and temperature conditions in hydrogen-rich environments. For this purpose, laboratory experiments are planned that will be carried out under different site-specific conditions with different gas phases (H2, H2-CH4, H2-CO2, CO2). Among other things, mineralogical-chemical, petrophysical and microbiological parameters will be investigated whose influence on, for example, the reservoir properties, the safety (impermeability) of the storage facilities and the fluid flow in the reservoir and along the wells will also be evaluated. This will make it possible to estimate the leakage risks in the case of cyclic hydrogen injections and withdrawals and the integrity of wells and reservoirs.
The German federal government’s goal to increase the proportion of wind energy in the German energy supply system, and at the same time prevent associated weather-related fluctuations in the electricity production, requires among other things that the energy can be converted into a medium that can be stored in the longer term. The production of hydrogen from water by means of electrolysis plays a key role in this regard. However, this also requires a fundamentally new concept for storing large amounts of electricity. One possible option would be geological storage in depleted natural gas or crude oil reservoirs and already existing natural gas storage facilities. However, it must be ensured that such sites can reliably and safely retain injected hydrogen or hydrogen-gas mixtures in order to prevent these gases from escaping to the surface in an uncontrolled manner. A particular weak point in many production and storage wells is the wellbore itself. Given the increased temperatures and pressures underground, the materials used for this purpose, such as steels, well cements and elastomeric seals, could react with the circulating pore fluids and existing or injected substances. Such corrosion, dissolution or alteration processes could lead to the (unwanted) ascent of gas or fluid phases, and thus impair the safety or impermeability of the storage facilities and harm the environment. HyINTEGER is therefore aiming to investigate possible interactions between the natural and technical components of underground storage sites and thus estimate the suitability of pore reservoirs for storing hydrogen.
Primarily, the researchers want to investigate the extent to which it is possible to store hydrogen in underground geological pore reservoirs in order to enable the longer-term storage of energy. Such an assessment presupposes that the hydrogen or hydrogen-carrying gas phases injected are, for example,
- safe, i.e. can be stored without the risk of uncontrolled leakages to the surface and thus without causing environmental damage,
- the recovery rates are economically feasible and
- that these reservoirs can be used for longer periods of time, i.e. across several injection and withdrawal cycles under ecological and economic aspects.
In particular, the investigations are focussing on the following three aspects: leakage risks along wells, mineralogical-chemical and microbiological reactions in the reservoir and along the wells, as well as in regard to the gas mixing processes in the reservoir.
Optimization and economic feasibility
The main focus of the planned work is on determining whether it is possible to continue using depleted natural gas and crude oil reservoirs and already existing natural gas storage sites within the planned and ongoing energy transition in order to ensure a secure and reliable energy supply in Germany. In connection with the findings obtained in the previous joint H2STORE project, numerous practical applications will be revealed from the investigations or (hoped) results from HyINTEGER. The experiments with different gas phases are relevant not only for storing hydrogen underground but also for (natural gas) pipeline systems and for generating green or synthetic methane – power-to-gas technology – for CCS/CCU applications. It is also relevant for geothermal energy projects, since the alteration and corrosion of well installations is also of key importance in this field. The collaboration already started in H2STORE and now continued in HyINTEGER with two international research projects, which are already implementing H2-CH4 mixtures in field-based demonstration projects, also verify the interest in and relevance of our work abroad in terms of achieving safe, economic energy storage and methanation reactions with hydrogen mixtures.
HyINTEGER is essentially carrying out basic research. Therefore there is no direct economic use for the expected results. However, these studies on the behaviour of hydrogen-carrying gas phases in natural geological reservoirs and for assessing leakage risks and the safety and impermeability of such reservoirs provide important (basic) information that is essential for the possible practical implementation of hydrogen storage and methane generation underground.
The focuses and work stages for the five participating sub-projects can be divided into the following main steps:
1. Selection of samples with project-supporting industrial partners on site. In addition to drill core material, this sample material also includes well piping and sealing components such as steel alloys, well cements and elastomeric compounds. Although this step is now completed, the industry shall continue to provide additional material if required during the project period.
2. Construction of experimental facilities (autoclaves) and conversion of laboratory rooms to ensure the (safety-related) requirements for conducting the planned experiments. This step has now been completed.
Production of composite samples from the various material components specified in 1.) for the planned tests. A series of composite samples have already been prepared and further composite samples are still being worked on (see Step 1).
4. Mineralogical, chemical, microbiological, physical and petrophysical characterisation of the sample material, whereby samples that are to be used in laboratory experiments (see next step) are being / have been investigated in detail.
This step has not yet been completed.
5. Conducting laboratory experiments with the main focus on evaluating possible mineralogical, chemical, microbiological and petrophysical changes to the sample material caused by the chosen experimental conditions and possible (different?) interactions between the material components during the experiments. These tests are being carried out under the pressure- and temperature-specific conditions provided by the storage locations with different gas phases (H2, CO2, H2-CO2, H2-CH4) and site-specific formation fluid compositions. - This work has been started.
6. Investigation of the sample material (on identical samples and with the same analytical methods) used in the experiments and interpretation of the datasets with regard to possible reactions; the data determined in Step 4 provides the reference points here. Dissemination of this information and data to the workgroups concerned for their numerical simulations.
This step is being successively met with the completion of the respective experiment series, whereby the initial results are expected in the summer of 2017.
7. Implementation of numerical simulations (modelling) for the following complexes: (a) Spread of gas phases underground, (b) Effects of cyclic injection and withdrawal gas phase operations on the reservoir and well, (c) Alteration of reservoir rocks, well cements, steels and elastomers, (d) Behaviour of biocenoses under different substrate conditions and in different gas compositions, (e) Influence of biofilms on the effective hydraulic reservoir parameters (porosity, permeability), (f) Changes in reservoir properties, particularly with regard to fluid pathways and in this context, (g) Effects of alteration (e.g. mineral dissolution, material embrittlement, corrosion) of the well components in regard to the safety/impermeability of hydrogen storage facilities (estimation of the leakage risk along the well). - Theoretical considerations in relation to these steps have already been carried out, and the first site-specific modelling based on the experimental results is expected in autumn 2017.
In Sub-project TP1, comparative mineralogical, petrographical, physical, geo-, hydro- and physico-chemical analyses as well as numerical simulations on materials before and after laboratory experiments are being conducted at Friedrich Schiller University Jena. By means of these comparisons, possible changes in the sample material induced by these experiments shall be verified and partly quantified. The experiments are being carried out in TPs 1-3 with different gas phases (H2, H2-CH4, H2-CO2, CO2) under site-specific pressure and temperature conditions (p ~ 5-20 MPa, T ~ 50-120 °C) on reservoir rocks, well cements, steel alloys and elastomers as well as on composite samples from these components. By means of flow simulations, the numerical modelling that is being performed with microtomographic datasets generated in TP 5 is aimed at revealing, for example, potential modifications to the pore structure that may have been caused by experimentally induced reactions. The aim of the work is to evaluate the influence of different gas phases on the reservoir properties and the integrity of the wells.
In Sub-project TP 2, which is being conducted by Clausthal University of Technology, petrophysical studies and high-pressure, high-temperature (HPHT) experiments are being carried out on the interactions between the hydrogen, reservoir rock, piping and cement in underground storage wells. For this purpose, the material being tested is subjected to in-situ pressure and temperature conditions. The investigations carried out on the test samples are intended to show the changes in the petrophysical properties of the materials used that are caused by geochemical interactions. The investigations should enable conclusions to be drawn about the suitability of the materials tested in terms of their deployment under the prevailing hydrogen storage conditions.
Sub-project TP3, which is being conducted by the GFZ German Research Centre for Geosciences (Microbial Geoengineering Working Group), is investigating the complex interactions between the materials used for installing and completing the wells and the rock, fluids and microbial community. Here various conditions, in particular with regard to temperature, pressure and salinity, will be considered. The interactions between the drilling fluids, piping, cementation and various installations will be investigated in variously complex experiments in order to increase geoscientific knowledge with regard to the influence of biological processes on the alteration and corrosion of materials. A major goal of the investigations is to assess the influence of microbial metabolic processes on the integrity of the wells and the corrosion of the surface and underground installations. Based on a greater understanding of the processes, guidance will be developed for more robust materials that are less suitable for providing a source of energy or nutrients for the microorganisms.
Conventional software packages for simulating flow processes in underground reservoirs are not capable of taking into account the microbial metabolic processes and the associated growth of biofilms. Therefore the development of suitable coupled mathematical models along with the numerical implementation and execution of exemplary simulation studies is planned in Sub-project 4. A model for the separation and transport of biofilms and the resulting change in the effective porosity and permeability shall be developed for the area near the well. Further simulations shall enable conclusions to be drawn about the microbially induced fluctuations of the gas composition on a field scale.
The aim of Sub-project TP5, which is being carried out by Johannes Gutenberg University Mainz (JGU Mainz), is to quantify the pore space-changing processes through dissolution and precipitation reactions by means of microcomputer tomography and numerical simulations based on it. To this end, the university is carrying out μXCT measurements on the samples both before and after the autoclave experiments conducted by the project partners, is quantifying the pore spaces and existing mineral phases and is conducting “Digital Rock Physics” (DRP) simulations, whereby it is also recording petrophysical parameters such as the porosity, permeability and effective diffusivity. Statistical methods are being used to determine representative elementary volumes (REV) on the structures, which will provide the basis for scaling up and transferring parameters (to TP4). In TP5, a module is being further developed that links together effective software codes for calculating physical and geochemical parameters and simulates the pore-scale reactive transport at the REV scale, based on the boundary conditions of the autoclave experiments.
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