Nanoengineered cement mixture could seal leaking gas wells

Leaking natural gas wells – including millions of abandoned gas wells – are a source of methane, a potent greenhouse gas. However, these wells are difficult to seal effectively. They can extend for miles beneath the ground and changes in temperature and pressure can degrade the cement used to seal pipes and casing. This eventually causes cracks to appear.

Now, researchers have developed a cement with special properties ideally suited for this purpose.

“We have invented a very flexible cement that is more resistant to cracking,” said Professor Arash Dahi, a petroleum engineering expert. “That’s important because there are millions of orphaned and abandoned wells around the world and cracks in the casings can allow methane to escape into the environment.”

Repairs involve injecting cement in extremely narrow spaces between the casing and surrounding rock.

“In construction, you may just mix cement and pour it, but to seal these wells you are cementing an area that has a thickness of less than a millimetre or that of a piece of tape,” said Dahi Taleghani. “Being able to better pump cement through these very narrow spaces that methane molecules can escape from is the beauty of this work.”

The Penn State researchers added nearly-2D graphite to cement slurry, through a multi-step process to uniformly distribute sheets of the material throughout the cement. Treating the graphite first with chemicals adjusted its surface properties, such that the material dissolves in water instead of repelling it.

“If we just pour this material in the water and mix it, these small particles have a tendency to stick together and form a conglomerate,” said Taleghani. “If they are not dispersing evenly then the graphite is not as strong inside the cement.”

The cement mixture was better for filling these very narrow spaces and was also stronger and more resilient. It can be used in active unconventional wells, such as those found in the Marcellus Shale gas play, as well as to seal orphaned and abandoned gas wells. It also shows promise for use in carbon capture and storage technology.

Graphite is more affordable than other nanomaterials previously used to bolster cement performance and very little is required to strengthen the cement mixture.

“Considering the low cost of the amount of graphite nanoplatelets required for this test, this technology may provide an economic solution for industry to address possible cementing problems in the field,” said Taleghani.