Natural Hydrogen and the Microbes That Consume It

In 1987, a water well drilled near Bourakebougou in Mali struck gas instead of water. The gas was almost pure hydrogen, and since 2012 it has fueled a generator supplying the village with electricity. No electrolysis was involved and no renewable power was consumed. The hydrogen is generated in the rock itself.

That well is a large part of why natural hydrogen, also called white or geologic hydrogen, has moved from geological curiosity to exploration target across the globe. If hydrogen can be produced the way natural gas is produced, the cost per kilogram drops well below what electrolysis currently delivers. What usually gets left out of that calculation is the subsurface itself. It is inhabited, and hydrogen is one of the best energy sources a microorganism can find.

How natural hydrogen forms

Hydrogen is generated continuously in the Earth's crust by a handful of geological processes. The best understood is serpentinization, in which water reacts with iron-rich rock at depth. The iron oxidizes, and hydrogen is released as a gas. Radiolysis adds to the inventory, splitting water molecules through radiation from decaying elements in the rock. Some of this hydrogen migrates upward and collects under a seal in the same way natural gas does.

Hydrogen as microbial food

Hydrogen is a strong electron donor, and in environments without oxygen it works as a kind of universal currency. Whole groups of microorganisms make their living from it. They need no light and no organic carbon, and many grow well at the temperatures, pressures, and salinities found in deep reservoirs.

The hydrogen consumers most relevant to a natural hydrogen system are:

• Sulfate-reducing bacteria and archaea, which pair hydrogen with sulfate and release hydrogen sulfide

  
  

• Methanogenic archaea, which combine hydrogen with carbon dioxide to form methane

  
  

• Acetogenic bacteria, which use the same two inputs to produce acetate

  
  

• Iron- and sulfur-reducing organisms that use hydrogen alongside mineral electron acceptors

  
  

Research on underground hydrogen storage in porous formations has shown that these reactions are not theoretical. Injected hydrogen has been observed to disappear into methane and hydrogen sulfide, and the withdrawn gas differs in composition from what went in. A natural hydrogen reservoir presents similar conditions with one difference. The hydrogen supply is not a finite injected volume but a system that keeps delivering substrate.

Cultivation of anaerobic microorganisms in an anaerobic chamber.  Samples must be kept out of air contact throughout all analyses.

Contamination during drilling

A reservoir that has been isolated for a long time may hold a sparse microbial community, limited by nutrients rather than by energy. Drilling changes that. Drilling fluids, makeup water, additives, casing, and tool surfaces all carry microorganisms from the surface. The operation that opens the reservoir can also inoculate it and feed it.

Once hydrogenotrophic organisms establish in a hydrogen-rich formation at a workable temperature, little stops them. The microbiological baseline therefore needs to be recorded before and during drilling rather than after a gas quality problem appears. Formation fluids exposed to air or depressurized on the way up give a distorted picture, because the organisms that matter most are the ones least able to survive that trip. High-pressure sampling and cultivation is what separates a community you can characterize from one you only see fragments of.

A high-pressure sampling vessel being operated during field sampling. The vessel captures formation fluid at reservoir pressure and keeps it sealed against air until it reaches the laboratory.

Gas quality and corrosion

Losing hydrogen to methanogens and sulfate reducers is the obvious problem. It is not the expensive one. Sulfate reduction produces hydrogen sulfide, which sours the gas, adds a purification step, and creates a safety issue at the wellhead. Acetogens acidify the water phase. Gas composition drifts away from the specification the project was built around.

The larger cost sits in the steel. Hydrogen-consuming organisms are among the main drivers of microbiologically influenced corrosion. Sulfate reducers generate sulfide directly at the metal surface inside a biofilm, where the local chemistry has little to do with the bulk fluid, and the result is pitting and sulfide stress cracking rather than uniform wall loss. Methanogens have been implicated in the direct uptake of electrons from iron surfaces. Organic acids from acetogens attack coatings and cement. Damage of this kind concentrates where flow is slow and water collects: dead legs, weld seams, crevices, and separator vessels.

Material selection for hydrogen infrastructure

Hydrogen-ready normally means two things: (i) The material has to be tight enough to hold a very small molecule, and (ii) it has to resist hydrogen embrittlement. Microbial corrosion is a third requirement, and it does not follow automatically from the first two. A polymer liner that solves permeation may be a good surface for biofilm attachment. A steel grade qualified for hydrogen service may still pit under a sulfide-producing biofilm. Elastomer seals and well cements can be degraded by the organisms and the acids they produce.

A microbiological assessment before construction usually covers:

• Baseline sampling of formation fluids and, where possible, core material

• Cultivation and identification of the hydrogen-consuming organisms actually present, not only their DNA signatures

• Corrosion testing of candidate materials against those organisms under realistic pressure and temperature

  
  

• A hygiene concept for drilling fluids and completion equipment

  
  

• A monitoring plan with defined sampling points and intervals for the operating phase

  
  

Cultivation matters more here than it might appear. Sequencing shows which organisms are present. It does not show which of them are active, how fast they grow, or how they behave against a particular alloy. The isolation of anaerobic microorganisms from a real formation sample is what allows a corrosion test to mean something.

View along the inside of a steel pipe. The upper wall carries pale grey and dark deposits, while a continuous rust-orange band runs along the bottom where water collects and flows. The pattern is localized attack at the water line rather than uniform wall loss.

Microbiology in the project timeline

Microbiology usually enters a hydrogen project after something has gone wrong: gas that smells of sulfide, a pressure drop nobody can explain, a failed inspection on a line that should have lasted decades. At that point, the options are limited and expensive. Bringing the same expertise in during exploration and detailed design changes what is possible, because material choices, drilling fluid specifications, and monitoring points are all still open.

Microbify supports natural hydrogen projects with sterile, anaerobic sampling in the field and with cultivation of the recovered organisms under the pressures they actually live at. We advise operators and engineering teams during the planning and construction of hydrogen infrastructure, from the first exploration well to the material specification for the surface plant. A hydrogen reservoir is far easier to work with when its microbiology is known early.