In a cross-disciplined approach, NETL researchers explore biogeochemistry and chemical reactions to help develop more effective ways to store carbon dioxide (CO₂) underground and enhance production of oil and natural gas, all while protecting the environment for future generations.

The work is cross-disciplined because it encompasses four specific areas.

Microbiology is the study of microscopic organisms.

Geology is the study of the rocks that make up the Earth.

Geomicrobiology is the study of microorganisms in geologic systems.

Geochemistry is the study of chemical changes in the Earth.

And so, biogeochemistry is the study of how all four of those areas interact.

The work requires an understanding of microbes—a diverse group of simple life forms that are invisible to the naked eye and abound in soil, the seas, and the air. In addition to a long list of other things good and bad, microbes cause decay of materials, ferment sugar to wine, make bread dough rise, sometimes cause disease, and produce products such as antibiotics and insulin.

They can also affect the porosity, permeability, acidity, and fluid chemistry of underground reservoirs where oil and gas fields are and where captured CO₂ is often stored. Porosity refers to the tiny spaces that exist within solid rock. Permeability is the ability of the rocks to allow fluids, gases or liquids to flow through. The chemical reactions caused by microbes can increase or decrease porosity and acidity.

In addition to subsurface biotic components—living or once-living organisms, researchers also study abiotic factors—nonliving elements like rocks and water. To ensure safe production of oil and gas, the long-term storage of CO₂, and effective wastewater management, it is important to keep tabs on how those biotic and abiotic components interact with the constantly changing chemical reactions occurring deep beneath the surface.

NETL is in a unique position to obtain hard-to-get samples in different energy environments to pursue the research. As the only Department of Energy national laboratory devoted to fossil energy research, the Laboratory can acquire unique but relevant samples from industry for biogeochemistry studies.

Yee Soong of NETL explained that one NETL geochemistry project examined a Lower Tuscaloosa sandstone sample to determine how geochemically induced changes in a sealing rock formation can predict CO₂storage capacity and long-term reservoir behavior.

“Saline aquifers are the largest potential continental geologic CO₂ sequestration resource,” Soong said. “Understanding the potential for geochemically induced changes to the porosity and permeability of host CO₂ storage and sealing formation rock will improve our ability to predict CO₂ plume dynamics, storage capacity, and long-term reservoir behavior. We need that to help decision makers keep tabs on the integrity of storage reservoirs.”

NETL’s Alexandra Hakala described another project intended to determine the extent of chemical reactions that occur between fracturing fluids used in hydraulic fracturing for oil and gas recovery and shale core in the Marcellus Shale play.

The project was conducted as part of NETL’s work with the Marcellus Shale Energy and Environmental Laboratory (MSEEL), a cooperative relationship involving West Virginia University, Ohio State University, Highpoint Construction, Northeast Natural Energy, and Schlumberger.

“NETL simulated pressure, temperature, and fluid flow rates replicating a four-day shut-in period,” Hakala said. “Core samples were obtained and a series of tests were executed, including CT [computed tomography] scans of the samples. The research showed that some mineral reactions occur between fracking fluid and the core, but no secondary activity along the primary fracture was detected. That information is important to have as the industry moves forward.”

Meanwhile, NETL’s Djuna Gulliver said the Laboratory’s geomicrobiology work is making important contributions to developing strategies for handling the produced water from hydraulic fracturing in the oil and gas fields.

“The extraction of gas and oil from shale formations using hydraulic fracturing generates large volumes of wastewater,” she said. “One of the challenges with managing that produced water is microbial activity because it could sometimes lead to issues with corrosion, sulfide release, and biofouling during and after operations.”

She said that is why NETL evaluated the structure, abundance, and metabolic potential of microbial populations from 42 Marcellus Shale produced water samples and 82 Bakken Shale produced water samples.

“Findings from this research enhance the current understanding of microbial community dynamics in produced water and will contribute to the development of better produced water management strategies in the future, with the goal of limiting corrosion, controlling fouling and souring issues, protecting well infrastructure, and minimizing unnecessary biocide application” Gulliver said.

The cross-disciplined biogeochemistry work that NETL is performing to characterize dominant microbial communities and understand how microbiological processes affect subsurface geochemistry is helping to improve our understanding of how these microbiological processes affect oil and gas production, carbon storage, and waste management. The microbial processes being researched at the Laboratory may also offer a promising option for alternative energy or enhanced energy recovery with less waste and reduced environmental impacts.