Nav: Home

Structure of fossil-fuel source rocks is finally decoded

November 13, 2018

CAMBRIDGE, Mass. -- The fossil fuels that provide much of the world's energy orginate in a type of rock known as kerogen, and the potential for recovering these fuels depends crucially on the size and connectedness of the rocks' internal pore spaces.

Now, for the first time, a team of researchers at MIT and elsewhere has captured three-dimensional images of kerogen's internal structure, with a level of detail more than 50 times greater than has been previously achieved. These images should allow more accurate predictions of how much oil or gas can be recovered from any given formation. This wouldn't change the capability for recovering these fuels, but it could, for example, lead to better estimates of the recoverable reserves of natural gas, which is seen as an important transition fuel as the world tries to curb the use of coal and oil.

The findings are reported this week in the Proceedings of the National Academy of Science, in a paper by MIT Senior Research Scientist Roland Pellenq, MIT Professor Franz-Josef Ulm, and others at MIT, CNRS and Aix-Marseille Université (AMU) in France, and Shell Technology Center in Houston.

The team, which published results two years ago on an investigation of kerogen pore structure based on computer simulations, used a relatively new method called electron tomography to produce the new 3-D images, which have a resolution of less than 1 nanometer, or billionth of a meter. Previous attempts to study kerogen structure had never imaged the material below 50 nanometers resolution, Pellenq says.

Fossil fuels, as their name suggests, form when organic matter such as dead plants gets buried and mixed with fine-grained silt. As these materials get buried deeper, over millions of years the mix gets cooked into a mineral matrix interspersed with a mix of carbon-based molecules. Over time, with more heat and pressure, the nature of that complex structure changes.

The process, a slow pyrolysis, involves "cooking oxygen and hydrogen, and at the end, you get a piece of charcoal," Pellenq explains. "But in between, you get this whole gradation of molecules," many of them useful fuels, lubricants, and chemical feedstocks.

The new results show for the first time a dramatic difference in the nanostructure of kerogen depending on its age. Relatively immature kerogen (whose actual age depends of the combination of temperatures and pressures it has been subjected to) tends to have much larger pores but almost no connections among those pores, making it much harder to extract the fuel. Mature kerogen, by contrast, tends to have much tinier pores, but these are well-connected in a network that allow the gas or oil to flow easily, making much more of it recoverable, Pellenq explains.

The study also reveals that the typical pore sizes in these formations are so small that normal hydrodynamic equations used to calculate the way fluids move through porous materials won't work. At this scale the material is in such close contact with the pore walls that interactions with the wall dominate its behavior. The research team thus had to develop new ways of calculating the flow behavior.

"There's no fluid dynamics equation that works in these subnanoscale pores," he says. "No continuum physics works at that scale."

To get these detailed images of the structure, the team used electron tomography, in which a small sample of the material is rotated within the microscope as a beam of elecrons probes the structure to provide cross-sections at one angle after another. These are then combined to produce a full 3-D reconstruction of the pore structure. While scientists had been using the technique for a few years, they hadn't applied it to kerogen structures until now. The imaging was carried out at the CINaM lab of CNRS and AMU, in France (in the group of Daniel Ferry), as part of a long-term collaboration with MultiScale Materials Science for Energy and Environment, the MIT/CNRS/AMU joint lab located at MIT.

"With this new nanoscale tomography, we can see where the hydrocarbon molecules are actually sitting inside the rock," Pellenq says. Once they obtained the images, the researchers were able to use them together with with molecular models of the structure, to improve the fidelity of their simulations and calculations of flow rates and mechanical properties. This could shed light on how production rates decline in oil and gas wells, and perhaps on how to slow that decline.

So far, the team has studied samples from three different kerogen locations and found a strong correlation between the maturity of the formation and its pore size distribution and pore void connectivity. The researchers now hope to expand the study to many more sites and to derive a robust formula for predicting pore structure based on a given site's maturity.
-end-
The work was supported by Royal Dutch Shell and Schlumberger through the MIT X-Shale Hub, and Total through the MIT/CNRS FASTER-Shale project.

ADDITIONAL BACKGROUND:

ARCHIVE: Structure of kerogen revealed https://news.mit.edu/2016/structure-kerogen-revealed-0201

Massachusetts Institute of Technology

Related Natural Gas Articles:

Visualizing chemical reactions, e.g. from H2 and CO2 to synthetic natural gas
Scientists at EPFL have designed a reactor that can use IR thermography to visualize dynamic surface reactions and correlate it with other rapid gas analysis methods to obtain a holistic understanding of the reaction in rapidly changing conditions.
Effects of natural gas assessed in study of shale gas boom in Appalachian basin
A new study estimated the cumulative effects of the shale gas boom in the Appalachian basin in the early 2000s on air quality, climate change, and employment.
The uncertain role of natural gas in the transition to clean energy
A new MIT study examines the opposing roles of natural gas in the battle against climate change -- as a bridge toward a lower-emissions future, but also a contributor to greenhouse gas emissions.
Natural-gas leaks are important source of greenhouse gas emissions in Los Angeles
Liyin He, a Caltech graduate student, finds that methane in L.A.'s air correlates with the seasonal use of gas for heating homes and businesses
Enhanced natural gas storage to help reduce global warming
Researchers have designed plastic-based materials that can store natural gas more effectively.
Natural gas storage research could combat global warming
To help combat global warming, a team led by Dr.
UT study shows how to produce natural gas while storing carbon dioxide
New research at The University of Texas at Austin shows that injecting air and carbon dioxide into methane ice deposits buried beneath the Gulf of Mexico could unlock vast natural gas energy resources while helping fight climate change by trapping the carbon dioxide underground.
Hydrogen-natural gas hydrates harvested by natural gas
A recent study has suggested a new strategy for stably storing hydrogen, using natural gas as a stabilizer.
Greener, more efficient natural gas filtration
MIT researchers have developed a new polymer membrane that can dramatically improve the efficiency of natural gas purification, while reducing its environmental impact.
Crystals that clean natural gas
A metal-organic framework that selectively removes impurities from natural gas could allow greater use of this cleaner fossil fuel.
More Natural Gas News and Natural Gas Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Uncharted
There's so much we've yet to explore–from outer space to the deep ocean to our own brains. This hour, Manoush goes on a journey through those uncharted places, led by TED Science Curator David Biello.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

Dispatch 2: Every Day is Ignaz Semmelweis Day
It began with a tweet: "EVERY DAY IS IGNAZ SEMMELWEIS DAY." Carl Zimmer – tweet author, acclaimed science writer and friend of the show – tells the story of a mysterious, deadly illness that struck 19th century Vienna, and the ill-fated hero who uncovered its cure ... and gave us our best weapon (so far) against the current global pandemic. This episode was reported and produced with help from Bethel Habte and Latif Nasser. Support Radiolab today at Radiolab.org/donate.