Understanding physics could lead to big gains in shale oil recovery

Credit: mining.com

A longer delay in the middle of an existing process could be the key to even greater success than is currently being achieved.

Oil companies are missing out on vast sums of recoverable oil in unconventional reservoirs, according to Penn State experts, as Phys.org reports.

The researchers propose that companies are applying tried-and-true transport mechanisms for conventional oil extraction but are hitting recovery stumbling blocks because they are not accounting for the difference in physics found at unconventional reservoirs.

Their research was published online in December in the Society of Petroleum Engineers' Journal.

"Unconventional reservoirs are enormous and offer significant hydrocarbon reserves," said Hamid Emami-Meybodi, assistant professor of petroleum and natural gas engineering at Penn State. "The scale of these reserves means that even a 1 percent change in recovery translates into a staggering quantity of oil. This untapped oil has motivated research on improved oil recovery from unconventional reservoirs using some conventional techniques."

More than half of the daily oil produced in the United States comes from unconventional formations. And that number is growing as companies tap into the nation's more than 35 billion barrels of oil in unconventional reserves, according to the U.S. Energy Information Administration.

Companies develop unconventional reservoirs by drilling long horizontal wells and creating hydraulic fractures to allow oil to flow for primary recovery, which currently ranges between 3 to 10 percent of the original oil mass in place.

They use commercial software developed based on Darcy's law to forecast oil recovery and reserves. But, in practice, they do not realize that Darcy's law—where flow is based on pressure differences—may not be appropriate for shale reservoirs, the researchers say.

After primary recovery, Emami said the existing industry practice is to use a conventional gas injection technique known as "huff 'n' puff" that improves oil mobility and increases recovery. During the "huff," the well and fractures are filled with a high-pressure gas, such as carbon dioxide or methane, which is followed by a short "soaking" period where the well is shut. The well is then opened during the "puff" to allow oil to be produced.

However, this conventional technique works poorly for shale formations, researchers say, because diffusion—not pressure differences—is what principally aids oil recovery in these formations containing nanometer-sized pores.

Continued here.

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