Oil produced from shale reservoirs drove record crude output in the U.S. over the past decade, but inefficiencies in extraction often leave as much as 90% of the oil behind, according to the federal Energy Information Administration.
To help maximize production from the tightly packed formations of shale rock, a team of researchers at Penn State developed a new oil extraction workflow that may improve shale oil recovery up to an additional 15% while providing long-term storage for carbon dioxide (CO2) emissions.
The workflow was successfully implemented for the Texas Eagle Ford Shale, where it demonstrated improvement in oil extraction, the researchers said, explaining that it can be expanded for application in other shale reservoirs. They reported their findings in the journal Fuel.
The innovation centers on improving cyclic CO2 injection, a process in which CO2 is pumped into the reservoir to enhance oil production. Also known as "CO2 huff-n-puff," the decades-old injection method bolsters extraction from naturally occurring rock formations. These rocks contain microscopic pores, called nanopores, where significant portions of hydrocarbons - the main component of oil - accumulate, according to the researchers.
Hamid Emami-Meybodi, associate professor of petroleum and natural gas engineering, faculty associate in Penn State's EMS Energy Institute and lead author, compared the underground shale environment to a sponge. Similar to the tiny openings in a sponge that fill with water, nanopores effectively soak up and retain hydrocarbons until the surface is disrupted.
"I would call this one of the best recycling systems in the industry," Emami-Meybodi said of the improved injection process. "Leveraging CO2 to bolster oil production eases environmental impacts, helps fulfill growing energy demand and contributes to the U.S.' energy independence and security."
During injection, CO2 is fed into the reservoir through a well. Then the well is shut to allow the injected gas to soak for a sufficient period. The gas mixes with the oil, altering its properties and improving oil mobility and extraction, according to the researchers.
By introducing CO2 in oil mixtures at different pressures, the injection process helps force hydrocarbons out of nanopores and to the surface. But the method's effectiveness varies widely with changing operational conditions, depths and oil types, the researchers noted.
"Optimizing injection is challenging due to numerous variables - including the oil properties and makeup of the shale environment - that can complicate extraction," Emami-Meybodi said.
