Studying the Eagle Ford above ground

Geologists hunt the Eagle Ford Shale miles below the surface in South Texas, looking for valuable oil and gas deposits.

But in West Texas, the formation can be seen a lot more easily — in a simple a highway cut, for instance.

Southwest Research Institute is running training field trips where geologists from oil and gas companies look at places where the Eagle Ford is exposed at the surface.

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The Eagle Ford Shale was deposited millions of years ago when much of Texas was a shallow sea. In South Texas where oil and gas drilling has boomed, it’s 50 miles wide and extends about 400 miles across the state, from the border to East Texas.

But the formation outcrops at the surface in the Dallas-Fort Worth Metroplex and west of Del Rio where it’s commonly called the Boquillas.

Southwest Research Institute’s field work gives geologists a better chance to look at the formation — a lot of it.

“Our field work focuses on exposures of the Eagle Ford/Boquillas formations in and around San Antonio, north and south of Del Rio, along Highway 90 west of Del Rio towards Dryden and into the Big Bend region,” Alan Morris, a staff scientist in the Geosciences and Engineering Division of Southwest Research Institute, said by email.

Usually geologists analyze samples of rock, called cores, taken from wells drilled thousands of feet below the surface.

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But looking at the traditional core samples alone doesn’t tell a geologist everything, Morris said, “because a 5-inch diameter core is not a good representation of many cubic miles of rock.”

Staff members with the Southwest Research Institute have been researching the rocks and structures for more than a decade, but started the Eagle Ford industry group last February.

They focus on the Eagle Ford, but the group also looks at the Austin Chalk, which sits above the formation, and the Buda Limestone, which lies beneath the Eagle Ford.

Although Morris said the difference between the Eagle Ford at the surface and the Eagle Ford miles below the ground can be significant, geologists can learn from how the rock weathers, study its natural deformations and see the variability in its mineralogy. They also can learn more about how the rock naturally fractures, which can instruct their drilling and hydraulic fracturing strategy.

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The membership fee for the consortium is $75,000 for each two-year phase, and so far eight companies are participating, although Southwest Research Institute said it couldn’t release a list for proprietary reasons.
But the project is likely to continue at the independent, nonprofit research and development organization.

“As long as there are geologists trying to find oil and gas, and rocks to look at, we will continue to help improve their and our understandings of the factors affecting energy extraction from rocks,” Morris said. “As the eminent British geologist H. H. Read said: ‘The best geologists are the ones who have seen the most rocks.’”