Relevance of Deep-Subsurface Microbiology for Underground Gas Storage and Geothermal Energy Production

Abstract

This chapter gives the reader an introduction into the microbiology of deep geological systems with a special focus on potential geobiotechnological applications and respective risk assessments. It has been known for decades that microbial activity is responsible for the degradation or conversion of hydrocarbons in oil, gas, and coal reservoirs. These processes occur in the absence of oxygen, a typical characteristic of such deep ecosystems. The understanding of the responsible microbial processes and their environmental regulation is not only of great scientific interest. It also has substantial economic and social relevance, inasmuch as these processes directly or indirectly affect the quantity and quality of the stored oil or gas. As outlined in the following chapter, in addition to the conventional hydrocarbons, new interest in such deep subsurface systems is rising for different technological developments. These are introduced together with related geomicrobiological topics. The capture and long-termed storage of large amounts of carbon dioxide, carbon capture and storage (CCS), for example, in depleted oil and gas reservoirs, is considered to be an important options to mitigate greenhouse gas emissions and global warming. On the other hand, the increasing contribution of energy from natural and renewable sources, such as wind, solar, geothermal energy, or biogas production leads to an increasing interest in underground storage of renewable energies. Energy carriers, that is, biogas, methane, or hydrogen, are often produced in a nonconstant manner and renewable energy may be produced at some distance from the place where it is needed. Therefore, storing the energy after its conversion to methane or hydrogen in porous reservoirs or salt caverns is extensively discussed. All these developments create new research fields and challenges for microbiologists and geobiotechnologists. As a basis for respective future work, we introduce the three major topics, that is, CCS, underground storage of gases from renewable energy production, and the production of geothermal energy, and summarize the current stat of knowledge about related geomicrobiological and geobiotechnological aspects in this chapter. Finally, recommendations are made for future research.

The deep-subsurface sulfate reducer Desulfotomaculum kuznetsovii employs two methanol-degrading pathways

“…High temperatures and oligotrophic conditions often prevail in deep-subsurface environments, which can be useful for underground gas storage and geothermal energy production 1 . However, the resident microbial communities influence possible applications, and these in turn affect the ecology of the deep-subsurface microbiota.…”

Microbial Biotechnology 2020; microbiology of fossil fuel resources

“…With respect to the environmental impact of fossil fuel exploitation and the technologies to mitigate this impact very little is yet understood about the influence of microbiology. For instance, we currently know little of the potential for favourable and unfavourable pH‐microbe‐mineral‐CO 2 interactions in deep storage facilities such as saline aquifers, depleted oil and gas reservoirs and even porous basaltic rocks which are likely to each have resident microbial communities (Gniese et al ., ).…”

Geobiotechnology II

“…Phospholipid-derived fatty acids (PLFA, cell membrane components) are used to estimate microbial biomass and can be assigned to certain microbial groups [116]. Phospholipid-derived fatty acids (PLFA, cell membrane components) are used to estimate microbial biomass and can be assigned to certain microbial groups [116].…”

“…Extraction of microbial cells from oil can be performed using organic solvents, such as n-hexane, methanol, or isooctane [120]. Extraction of microbial cells from oil can be performed using organic solvents, such as n-hexane, methanol, or isooctane [120].…”