To reduce global warming an energy transition going from fossil fuel to renewable energy is required and energy storage opportunities to store surplus electricity are needed. Hydrogen gas (H2) is an energy carrier and can be stored in surface tanks or in geological subsurface formations. Underground hydrogen storage (UHS) offers a large storage capacity suitable for long-term storage. However, high abundance of subsurface microbes using H2 in their metabolism has undesirable side effects for UHS. Microbes may cause H2 loss, H2S formation, and clogging and microbial behavior and H2 loss mechanisms need to be studied before implementing UHS technology. This study focuses on how the sulfate-reducing bacteria (SRB) Oleidesulfovibrio alaskensis consumes H2. Laboratory experiments have been performed to increase understanding of how this strain will act in the context of UHS. Suitable storage gas mixtures, the impact of pressure, increasing surface area, and pH were studied to improve the knowledge of SRBs impact on H2 consumption in the subsurface. Also, a micromodel experiment was performed to investigate the H2 consumption in porous media. Generally, the results showed that Oleidesulfovibrio alaskensis completely consumed H2 where the consumption rate was dependent on the growth conditions. More optimal growth conditions increased the consumption rate. A rapid pH increase, above the maximum growth ph of 9, was observed for this strain giving the microbes less optimal growth conditions. Nevertheless, other factors than pH seemed to be more crucial for the H2 consumption rate for this strain. Investigation of pressure impact showed no significant differences in the H2 consumption rate, assumingly due to the low pressures used for these experiments. Similar H2 consumption rates per cm2 were observed when testing larger gas-liquid contact areas, indicating that larger surface areas are not consuming more H2 per cm2 . Movements in the aqueous phase seemed to increase the solubility of H2 causing higher H2 consumption rates compared to static conditions. In the micromodel experiment, the H2 consumption stopped before all the H2 were consumed. The stop in H2 consumption may be due to the low amount of microbial cells or factors limiting microbial movement like physical hindrances of the pore structure or produced bioproducts inhibiting microbial growth. pH may also affect the consumption in the micromodel but need further investigations. Obtained results indicate microbial activity in the subsurface as a challenge for UHS. However, research on other SRBs is needed to improve the understanding of how microbes are consuming H2. Also, core-scale and field-scale experiments are needed to investigate how the microbes are acting under reservoir conditions and in the presence of other chemicals available in the subsurface environment.Masteroppgave i energiENERGI399I5MAMN-ENE
