Ad hoc devices, which Almajid and his colleagues painstakingly craft and assemble by hand, are designed to force pressurized oil, water or gas through slim cylinders of seemingly solid rock, which the scanners then analyze with X-rays.
Above – CT scanner in the lab of Anthony Kovscek conducts experiments meant to mimic the flow of liquids and gases deep underground. (Image credit: Ker Than)
“We try to visualize things that people say you can’t visualize,” said Kovscek, who is the Keleen and Carlton Beal Professor of Petroleum Engineering at Stanford. “It’s happened more than once, where someone will say, ‘Well, you just can’t do it.’ And I point to our results and say, ‘Well, I beg to differ.’”
The lab experiments are intended to recreate, in miniature, the movement of various substances through vast rock formations and to provide real-world validation of computer simulations of the same processes. This type of experimentation and simulation has helped the United States move toward energy security by enabling the nation to tap vast reserves of previously inaccessible oil and natural gas, such as shale oil.
But what’s learned from that mass of tubes and gauges could also help mitigate the effects of burning 100 million barrels of oil per day, which is expected to continue for at least 50 years while the world transitions to renewable energy sources. Results like the ones from Kovscek’s lab are now guiding new ways of sequestering the powerful greenhouse gas carbon dioxide, which is released from burning fossil fuels, deep within rocks, for eons, while avoiding leaks and other negative consequences – a strategy many experts say is going to be necessary in order to avoid the hazards of climate change.
“Greater efficiency in oil recovery and conversion of the energy system to renewables has to happen.
Trapping carbon underground
Some of the strategies for efficiently extracting oil and natural gas from reservoirs that came out of work like Kovscek’s are also a first step toward carbon sequestration.
Especially relevant is a practice called enhanced oil recovery (EOR) by gas injection, which involves pumping pressurized gases into existing oil fields to displace or reduce the viscosity of crude oil, making it easier to extract. Even the best performing fields still leave about 50 percent of oil in the ground, Kovscek said. For unconventional resources such as shale rocks, which are even more difficult to extract oil from, the recovery rate can be as low as 5 percent.
Despite the risks of leakage, Tchelepi said the results from Kovscek’s scanner experiments and his own team’s computer simulations indicate that safe, long-term carbon sequestration is within reach — and he thinks the technique should be deployed now, even though it’s still in its infancy. “It’s far from being perfected, but we know more than enough, in my opinion, to start using it,” Tchelepi said. “Clearly, there will be issues and problems, but the only way to deal with them is to put them under the control of science and engineering, to monitor them and to spend the resources to learn from the mistakes. The risk of waiting for perfection is too big. We know enough.”
One idea that Kovscek and Tchelepi’s labs are exploring is combining EOR and carbon sequestration to create what they refer to as “green oil.” “If you can take all of the CO2 that is generated from burning the oil or natural gas that’s extracted in the future from a reservoir, inject it back into the reservoir and store it securely, you would have net-zero carbon emissions,” Kovscek said. “Sequestration is expensive. If we can recover something valuable in the process, it can be used to pay for the sequestration.”
While some might see a contradiction in helping maximize the extraction of oil and natural gas, on the one hand, and working to sequester the CO2 created from the burning of those same fuels on the other, Tchelepi views the two goals as complementary.
“You have to be realistic that we will use 100 million barrels of oil a day for the next 50 years,” he said. “Should we do that in a messy, uncontrolled way? Or should we do it with the best possible engineering, maximize the recovery and optimize it by coupling it with sequestration? I’m working on the second option.”