International team of scientists finds new type of natural gas

Among Alberta’s incredible geological features are its vast shale deposits; these are among the richest sources of natural gas on the continent, with the so-called unconventional hydrocarbon reservoirs in the province containing over 1.29 trillion cubic feet of gas.

Dr. Bernhard Mayer, PhD, professor in the Department of Geoscience, is part of an international research collaboration that has recently discovered a previously overlooked gas formation process in black shales. Through detailed analysis, the research team — comprising experts from the Bureau de Recherches Géologiques et Minières (BRGM or French Geological Survey), Canada, and Switzerland — was able to demonstrate that this type of gas formation process exists in numerous shale formations throughout the world.

The new study, lead authored by BRGM postdoc Maria Naumenko Dèzes, will help build greater understanding of how unconventional gas resources are formed, and will refine current approaches to identify the sources of possible gas leaks near wells.

The results were recently published in the journal PNAS.

Fourth type of natural gas has implications for environmental monitoring

To date, three main sources of natural gas — microbial, thermogenic, and abiotic — had been identified. This new research shows that there is a fourth source of natural gas, generated by radiolysis — the dissociation of molecules by ionizing radiation — of the organic matter in shale rock.

At first glance, the data shows that this new type of gas is chemically not significantly different from thermogenic natural gas. However, the research team found that over hundreds of millions of years, the natural radioactivity of radioelements such as uranium in shales can interact with organic matter to produce some natural gas composed of methane, ethane, and propane that has a unique isotopic fingerprint.

The discovery is potentially important from an environmental monitoring viewpoint.

“If regulators are looking for environmental impacts from shale gas development, for instance, it has a number of implications,” Mayer explains. “Previously, when ethane or propane were found in groundwater, the immediate assumption was that a deep thermogenic gas had leaked into the shallow groundwater from a couple of kilometres below the surface; the most likely culprits for such gas migration are oil and gas wells that are not properly sealed.”

Finding ethane or propane has always raised a red flag that a nearby leaky well may be contaminating groundwater. “In my view, this new discovery means that if there are thick, organic-rich shales underneath the shallow groundwater, it could be that this newly discovered type of gas is seeping up

“This is definitely something we will test in the future. It will take us a couple of years to sort this out, but it may not be as simple as we’d previously thought,” adding that the research team’s goal is to describe the process as accurately as possible and avoid ascribing detrimental environmental impacts to circumstances that cannot be verified.  

Technological advances allow for ‘new twist on old story’

To find their results, the researchers combed through years of data, some of which built upon work done by fellow Faculty of Science geoscience professor Dr. Steve Larter, PhD, and Mayer’s joint research project on environmental baseline conditions prior to shale gas development jointly funded by NSERC and the French National Research Agency (ANR). 

Mayer says this new source of natural gas had previously been overlooked, and has only been discoverable in the past 15 years due to technological advancements.

“In the past, producers looked for oil and gas in conventional reservoirs, which do not contain much uranium or large amounts of organic matter,” Mayer explains. “It is only since the industry started to do shale gas exploration with horizontal drilling and hydraulic fracturing that we have been able to access shale reservoirs that may contain elevated uranium and organic matter contents.

"There’s good reason why nobody found it over the last hundred years, as we’ve only been drilling in these unconventional hydrocarbon reservoirs where this process occurs for less than two decades.”

This new source of gas is often a small contribution of what the researchers find, but in some cases, it can comprise up to 25 per cent of the natural gas that is produced in shale gas plays that have high organic matter and uranium contents.

Mayer believes the biggest impact will be in environmental monitoring. “When it comes to finding ethane and propane in groundwater, we now need to consider that it could be from this previously overlooked gas source, as opposed from automatically being due to a leaky oil and gas well,” he says.

“It’s a new twist to an old story."