A recent study conducted at Kyoto University in Japan and published in the online version of New Scientist, claims compressed carbon dioxide may be more suitable for fracturing methane-rich rock than water. Shahab Mohaghegh, a professor of petroleum and natural gas engineering at West Virginia University and an expert in well modeling, says the study may hasten the development of large-scale carbon sequestration.
Natural gas production has soared worldwide in recent years as a result of hydraulic fracturing, or fracking, a process of injecting pressurized water into shale formations to fracture the rock and release natural gas trapped inside. The more extensive the network of fractures created in the shale, the more pathways are available for the gas inside it to escape. Researchers at Kyoto University have now found a way to greatly extend that network of fractures by replacing pressurized water with liquid or supercritical CO2.
Mohaghegh is studying the technical and economic viability of using CO2 to remove methane from shale, but from a different perspective.
“We have very limited hands-on experience injecting CO2 into shale formations, so most of what we do has to be simulated through modeling studies,” Mohaghegh said. “And these types of models tend to be extremely large, made up of millions of grid blocks or cells. Each question or run that is proposed through traditional modeling techniques would take a day at least to answer.”
Using a technique he developed, which involves artificial intelligence and data mining, Mohaghegh and his team of student researchers have been able to build surrogate reservoir models or SRMs, which replicate the extremely large models, but run in real time.
“Instead of it taking a day to make a run, it happens instantly,” Mohaghegh said. “We can literally make millions of simulation runs and show the benefits or the limitations to injecting CO2 into the formation.”
Shale, Mohaghegh said, has a greater affinity for CO2 than methane. When CO2 is injected into a depleted shale formation—even one that has previously been fracked —the rock will release more methane because pockets of the gas chemically trapped within the shale will be released in favor of the more chemically attractive CO2.
“Shale is an incredible storage source and carbon sequestration can help us release more methane,” Mohaghegh said. “If you can also use carbon dioxide to fracture the rock, that would add a third dimension that could be more significant than sequestration or enhanced recovery.”
The technology, which is still in its infancy, is being developed as part of a grant Mohaghegh received from the Department of Energy through the American Recovery and Reinvestment Act.
New Scientist notes that a 2006 study by the U.S. Department of Energy assessed geologic sequestration options in the midwest. It found that saline aquifers offer by far the greatest potential carbon storage capacity, with shale beds that have been fractured for methane production coming in second.
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CONTACT: Mary C. Dillon