Underground Storage of Hydrogen: In Situ Self-Organisation and Methane Generation

Abstract

In situ observations have shown that underground storage of hydrogen behaves like a natural chemical reactor and generates methane. The mechanism of this generation is the metabolic activity of methanogenic bacteria which consume hydrogen and carbon dioxide and transform them into methane and water. The coupled mathematical model of the reactive transport and population dynamics in a storage is suggested in this paper which also takes into account the fact that the population growth rate depends on the structure of the bacterium colony. The suggested system of equations is reduced to the Turing reaction-diffusion model which proves the appearance of non-attenuating self-oscillations in time which are uniform in space. These solutions are unstable and, once perturbed, generate regular spatial stationary waves which correspond to the alternations of zones which are rich in CH 4 or CO 2 . This result predicts the effect of a natural in situ separation of gases, which was observed in practice. If the diffusivity of bacteria is neglected with respect to the effective diffusivity of the injected gas, then only large-scale spatial waves arise. A low but non-zero bacterium diffusivity causes the appearance of additional small-scale linear oscillations whose period is the intrinsic parameter of the process and is proportional to the bacteria-gas diffusivity ratio. The analysis is completed with numerical simulations of 2D problems and analytical solutions of 1D problems obtained using the technique of two-scale asymptotic expansion. The estimations for the parameters of the model were obtained.

Hydrogenization of underground storage of natural gas

“…None of the models shows the lag and stationary phases which have been observed in batch culture experiments. Only the model of [29] shows the acceleration phase. -The purely hydrodynamic simulation study has shown the importance of the injection rate.…”

“…In the literature, two bio-reactive transport models are available which were developed for the application to UHS: [14] developed a model at pore scale while [29] and [34] developed a model at macroscopic scale. Additionally, there is a large number of models for bio-reactive transport in groundwater which are constrained to single-phase flow.…”

“…For all of them, the growth starts immediately and the deceleration phase continues directly in the decay phase. Only the model of [29] shows the acceleration phase. The Monod and Moser model start directly with the exponential growth phase.…”

Numerical simulation of hydrodynamic and gas mixing processes in underground hydrogen storages

“…A completely different operation strategy, called the ''selective technology'' was suggested in Hagemann et al (2015) and Panfilov (2010). The idea is to use an aquifer where horizontal impermeable or almost impermeable barriers exist.…”

Mathematical modeling of unstable transport in underground hydrogen storage

“…Another problem considered by Panfilov (2010) and Toleukhanov et al (2012) is the increased activity of microorganisms in the subsurface due to the injection of hydrogen. Hydrogen is a universal electron donor for several microbial species (including archaea and bacteria), which means that it will be metabolized into other substances.…”