Pattern formation in underground hydrogen storage and in-situ biomethanation

Underground bio-methanation entails the conversion of surplus renewable electricity into hydrogen (H 2 ), then storing the hydrogen and carbon dioxide (CO 2 ) in a geological formation, and the conversion of the mixture into methane (CH 4 ) using methanogenic bacteria. The method offers the dual benefit of storing renewable electricity and recycling carbon dioxide simultaneously. However, in-situ observations have revealed that the system’s mixture is difficult to control due to the emergence of non-attenuating self-organizing patterns. These structures result in the formation of zones of high methane concentration and other of high carbon dioxide concentration, a typical behavior for non-linear reaction-diffusion systems. The spatial heterogeneity of the gas distribution implies incomplete methanation, which consequently affects the quality of the gas produced. To resolve this issue, it is necessary to determine the limits of the pattern zone with respect to the process parameters and to maintain the system outside of this zone. In this paper, we analyze the criteria that lead to the emergence of patterns. We demonstrate the appearance of different regimes including stationary patterns driven by Turing’s instability and uniform pattern in space but periodically oscillating in time associated with the phenomenon of Hopf-Andronov bifurcation. We introduce novel spatio-temporal patterns known as jumping waves. To our knowledge, this is the first time such a result is demonstrated in the context of Underground Hydrogen Storage (UHS).