Enabling large-scale hydrogen storage in porous media – the scientific challenges

Expectations for energy storage are high but large-scale underground hydrogen storage in porous media (UHSP) remains largely untested. This article identifies and discusses the scientific challenges of hydrogen storage in porous media for safe and efficient large-scale energy storage to enable a global hydrogen economy. To facilitate hydrogen supply on the scales required for a zero-carbon future, it must be stored in porous geological formations, such as saline aquifers and depleted hydrocarbon reservoirs. Large-scale UHSP offers the much-needed capacity to balance inter-seasonal discrepancies between demand and supply, decouple energy generation from demand and decarbonise heating and transport, supporting decarbonisation of the entire energy system. Despite the vast opportunity provided by UHSP, the maturity is considered low and as such UHSP is associated with several uncertainties and challenges. Here, the safety and economic impacts triggered by poorly understood key processes are identified, such as the formation of corrosive hydrogen sulfide gas, hydrogen loss due to the activity of microbes or permeability changes due to geochemical interactions impacting on the predictability of hydrogen flow through porous media. The wide range of scientific challenges facing UHSP are outlined to improve procedures and workflows for the hydrogen storage cycle, from site selection to storage site operation. Multidisciplinary research, including reservoir engineering, chemistry, geology and microbiology, more complex than required for CH4 or CO2 storage is required in order to implement the safe, efficient and much needed large-scale commercial deployment of UHSP.This work was stimulated by the GEO*8 Workshop on “Hydrogen Storage in Porous Media”, November 2019 at the GFZ in Potsdam (Germany). NH, AH, ET, KE, MW and SH are funded by the Engineering and Physical Sciences Research Council (EPSRC) funded research project “HyStorPor” (grant number EP/S027815/1). JA is funded by the Spanish MICINN (Juan de la Cierva fellowship-IJC2018-036074-I). JM is co-funded by EU INTERREG V project RES-TMO (Ref: 4726 / 6.3). COH acknowledges funding by the Federal Ministry of Education and Research (BMBF, Germany) in the context of project H2_ReacT (03G0870C).Peer reviewe

Scoping carbon dioxide removal options for Germany–What is their potential contribution to Net-Zero CO2_{2}?

In its latest assessment report the IPCC stresses the need for carbon dioxide removal (CDR) to counterbalance residual emissions to achieve net zero carbon dioxide or greenhouse gas emissions. There are currently a wide variety of CDR measures available. Their potential and feasibility, however, depends on context specific conditions, as among others biophysical site characteristics, or availability of infrastructure and resources. In our study, we selected 13 CDR concepts which we present in the form of exemplary CDR units described in dedicated fact sheets. They cover technical CO2 removal (two concepts of direct air carbon capture), hybrid solutions (six bioenergy with carbon capture technologies) and five options for natural sink enhancement. Our estimates for their CO2 removal potentials in 2050 range from 0.06 to 30 million tons of CO2, depending on the option. Ten of the 13 CDR concepts provide technical removal potentials higher than 1 million tons of CO2 per year. To better understand the potential contribution of analyzed CDR options to reaching net-zero CO2 emissions, we compare our results with the current CO2 emissions and potential residual CO2 emissions in 2050 in Germany. To complement the necessary information on technology-based and hybrid options, we also provide an overview on possible solutions for CO2 storage for Germany. Taking biophysical conditions and infrastructure into account, northern Germany seems a preferable area for deployment of many concepts. However, for their successful implementation further socio-economic analysis, clear regulations, and policy incentives are necessary

Net‐Zero CO 2 Germany - A Retrospect From the Year 2050

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

Heuristic Methods for Pipeline Network Design

We showcase geospatial heuristic methods for network design and optimization. We propose and adapt graph algorithms to achieve optimal (or close to optimal) fluid transportation networks meeting quantifiable criteria (such as minimizing cost for example). Typically, these are used on pipeline infrastructure design, for CO2 collection or H2 distribution for example. The pipeline cost functions involved in the optimization depend on both pipeline length and a concave function of pipeline capacity. As such, discrete optimization methods are required. We have extended the tool to integrate other known aspects of network design. A sink placement algorithm can identify the minimum-cost storage location (and in parallel construct the rest of the a priori unknown network structure). The tools have finally been adapted to allow the inclusion of pre-existing pipeline infrastructure at a lower cost. They can then propose networks that prioritize planning along pre-existing pipeline routes

Hydrogen storage in porous media: learnings from analogue storage experiences and knowledge gaps

EGU2020: Sharing Geoscience Online, 4-8 may 2020Underground hydrogen storage (UHS) in porous media has been proposed as an effective and sustainable energy storage method to balance renewable energy supply and seasonal demand. To determine the potential for and conduct realistic risk assessments of the UHS technology, learnings from more mature underground fluid storage technologies, such as underground storage of natural gas (UGS) or CO2 (UCS), can be used. Here we discuss the caveats related to the use of these technologies as analogues to UHS and highlight current knowledge gaps that need to be addressed in future research to make UHS a secure and efficient technology. Abiotic and biotic reactions between the rock and the fluids, often not considered in UCS and UGS operations, play an important role in UHS and can change the chemical environment in the reservoir dramatically. The mineralogy of the reservoir and cap rocks, as well as the in-situ pore fluid chemistry, is of vital importance and the characterisation efforts should not be limited to the reservoir quality. The risk assessment of UHS operation may follow similar production cycles as in UGS, but there are important lessons to be learnt from UCS. UCS aims to store injected gas permanently and different CO2 trapping mechanisms are contributing to storage security. Residual trapping, which locks parts of the CO2 within the pore space, may reduce the commercial profitability in UHS, but can assist to mitigate potential leakage of hydrogen. The dissolution of hydrogen in the pore water will likely play a minor role in UHS compared to UCS, while the precipitation of minerals containing hydrogen during UHS has not yet been appropriately investigated. The main storage process in gas storage is the accumulation of buoyant fluid underneath a low-permeability cap rock in a three-dimensional trap. Storage sites are determined by different parameters: UGS is mainly used in depleted gas fields (hence sites with proven gas storage security), while UCS sites are usually located deeper than 800m for efficiency reasons, under conditions at which CO2 is present as a high-density supercritical phase. None of these restrictions are a pivotal for UHS and a new set of constrains should be formulated specifically designed to the properties of hydrogen. These must involve: The unique properties of hydrogen (high diffusivity and low density and, thus, high buoyancy) require potential storage sites to have well-understood cap rocks with minimal diffusion and capillary leakage risk. A reservoir architecture and heterogeneity that guarantees economically sensible injection and withdrawal rates by choosing sites, which minimise the isolation of hydrogen from the main plume during UHS operations. Site monitoring protocols will also need to be re-evaluated for different scales, as well as for the dynamic properties of hydrogen, such as low density and fluid mobility. It is certain that leakage along abandoned wells, the main risk for leakage in UCS and UGS, will also pose a risk to the containment of injected hydrogen. Therefore, hydrogen storage site locations require a comprehensive investigation into abandoned and operational (deep) petroleum and (shallow) water exploration and production wells

CO2 Migration Monitoring by Means of Electrical Resistivity Tomography (ERT) – Review on Five Years of Operation of a Permanent ERT System at the Ketzin Pilot Site

At the Ketzin pilot site, Germany, electrical resistivity tomography (ERT) is a substantial component in a multi-disciplinary monitoring concept established in order to image CO2 injected in a saline aquifer. Since more than five years, crosshole ERT data sets have repeatedly been collected using a borehole electrode array acting as a permanent reservoir monitoring tool. This contribution summarizes the aspects being essential for a successful deployment and operation of such a downhole installation. It is shown that the presented installation can facilitate stable and reliable data collection at least throughout the investigated five- year period of ongoing CO2 injection. Based on the experiences being gained so far, it is concluded that a properly calibrated and integrated downhole ERT system allows for mapping of quantitative CO2 saturation estimates in the subsurface.ISSN:1876-610

Monitoring freshwater salinization in analog transport models by time-lapse electrical resistivity tomography

Deep saline aquifers are target formations both for the geological storage of carbon dioxide as well as for geothermal applications. High pressure gradients, resulting from fluid or gas injection processes, provide a potential driving force for the displacement of native formation waters, implicating a potential salinization of shallow freshwater resources. Geoelectrical monitoring techniques are sensitive to compositional changes of groundwater resources, and hence capable to detect salinization processes at an early stage. In this context, numerical simulations and analog modeling can provide a valuable contribution by identifying probable salinization scenarios, and thereby guiding an optimum sensor network layout within the scope of an early warning system. In this study, coupled numerical flow and transport simulations of a laterally uniform salinization scenario were carried out and used to support a subsequent realization in a laboratory sandbox model. During the experiment, electrical resistivity tomography (ERT) was applied in a practical surface–borehole setup in order to determine the spatio-temporal variations of electrical properties influenced by saltwater intrusion. Inversion results of different electrode configurations were evaluated and compared to numerical simulations. With regard to surface–borehole measurements, good results were obtained using crossed bipoles, while regular bipole measurements were more susceptible to noise. Within the scope of a single-hole tomography, the underlying resistivity distribution was best reproduced using the Wenner configuration, which was substantiated by synthetic modeling.ISSN:0926-9851ISSN:1879-185

Heuristic Methods for Minimum-Cost Pipeline Network Design: A Node Valency Transfer Metaheuristic

Designing low-cost network layouts is an essential step in planning linked infrastructure. For the case of capacitated trees, such as oil or gas pipeline networks, the cost is usually a function of both pipeline diameter (i.e. ability to carry flow or transferred capacity) and pipeline length. Even for the case of incompressible, steady flow, minimizing cost becomes particularly difficult as network topology itself dictates local flow material balances, rendering the optimization space non-linear. The combinatorial nature of potential trees requires the use of graph optimization heuristics to achieve good solutions in reasonable time. In this work we perform a comparison of known literature network optimization heuristics and metaheuristics for finding minimum-cost capacitated trees without Steiner nodes, and propose novel algorithms, including a metaheuristic based on transferring edges of high valency nodes. Our metaheuristic achieves performance above similar algorithms studied, especially for larger graphs, usually producing a significantly higher proportion of optimal solutions, while remaining in line with time-complexity of algorithms found in the literature. Data points for graph node positions and capacities are first randomly generated, and secondly obtained from the German emissions trading CO2 source registry. As political will for applications and storage for hard-to-abate industry CO2 emissions is growing, efficient network design methods become relevant for new large-scale CO2 pipeline networks.Petroleum Engineerin