On November 2, the project "Plan to Update the Current State of Knowledge Regarding the Oxygen Limit (10 ppm) in Underground Gas Storage Facilities" was launched.
Background and Motivation
DGMK Report 753 (2013) summarizes the state of the literature as of 2013 and discusses the limit value of 0.001 mol‑% (10 ppm) O₂ set forth in the draft version of the DVGW Worksheet G 260 at the transfer point to the high-pressure network and at underground gas storage facilities (UGS) [1]. As early as 2013, it was determined that biogas typically has O₂ concentrations of 0.2–1 mol⁻¹TP6T and thus meets the network limit value but may exceed the storage limit value when fed into the system in larger quantities.
Since then, some of the underlying conditions have changed, making it necessary to update the study:
• Expansion of biomethane injection: a quantitative increase in injection points and injected volumes in Germany and the EU; resulting in rising relative O₂ loads in the transmission and distribution networks. The transmission network is currently still largely unaffected, but the first injection points with recompression into the high-pressure network already exist.
• New field and model data: Field data sets spanning several years on O₂ reactivity in real reservoirs are now available, allowing for an empirical verification of the threshold value, which had previously been derived largely from theory.
• Updated regulations: Revised DVGW G 260 (2021), CEN/DIN EN 16723 (biomethane specification), ENTSOG and GERG reports on O₂ management in the European gas network, and H₂-specific guidelines (DVGW, ISO 14687)
• Microbiological/geochemical interactions: New research findings are available on sulfate reduction, methanogenesis, H₂S formation, pyrite oxidation, and "black powder" formation under real UGS conditions.
• Corrosion: In recent years, extensive studies on corrosion in steels have been conducted in connection with H₂. However, the test conditions must be compared with those in the storage facilities (pressures, gas composition, such as moisture content).
The goal of this update is to provide a reliable, citable basis for the ongoing discussion on whether the 10-ppm limit should be raised, maintained, reduced, or revised on a case-by-case basis depending on storage type and gas type.
Objective
The project aims to:
• systematically compile the current state of knowledge (DGMK Report 753), published since 2013, regarding the effects, prevention, and controllability of O₂ in natural gas and H₂ in underground gas storage facilities and high-pressure networks,
• Review the technical and scientific rationale for the 10-ppm limit and compare it with current data,
• Provide quantitative information on reaction pathways, kinetics, and tolerable O₂ concentrations (pore, aquifer, and cavern storage) for the relevant gases (natural gas, H₂, mixtures). With regard to the various gases, it must be assessed whether, if at all,.
Differences in damage patterns allow for a differentiation of O₂ concentrations
would.
• Formulate an assessment of the 10 ppm limit from the perspective of storage facility operators.