The great oil and gas formations that U.S. shale drillers thrive on have reportedly been traced back to volcanic eruptions from the time of the dinosaurs, over 100 million years ago.
In the Cretaceous time, the era of the dinosaurs, an enormous flare-up of volcanic activity spewed ash with high levels of carbon dioxide and nutrients that helped more organic carbon to be buried in the earth, generating an abundance of hydrocarbon source rocks from Texas to Montana, Rice University geologists said in a new study published in Nature Publishing’s online journal Scientific Reports.
There have always been hints that volcano eruptions in dinosaur times could be linked to shale oil and gas resources, said study lead author Cin-Ty Lee, professor and chair of Rice’s Department of Earth, Environmental and Planetary Sciences.
Now the study by Lee, graduate student Hehe Jiang, and Rice undergraduates Elli Ronay, Jackson Stiles and Matthew Neal, in collaboration with Daniel Minisini at Shell, suggests that volcanic ash and the nutrients carried in it may have increased the efficiency of biological productivity and organic carbon preservation in the Cretaceous period.
In those times, the climate on Earth resembled that of greenhouse, sea levels were high, much of western North America lay beneath a shallow ocean, and carbon dioxide in the atmosphere was more than ten times higher than it is today. Related: Here’s What’s Next For Electric Cars
On a field trip to West Texas in 2014, Lee and his team were studying how volcanoes in the Cretaceous had affected the Earth’s climate and noticed hundreds of ash layers in exposed rock that dated to that period.
“We had seen ash layers before, but at this site we could see there were a lot of them, and that got us thinking,” Lee said.
What they thought of was the so-called “dead zones” in oceans—areas with such low oxygen levels that animal life suffocates and dies.
Today, farm overfertilization creates large volumes of phosphorus in rivers, and when that element makes its way to the ocean, phytoplankton eat all the nutrients and multiply so quickly that they drain those areas of oxygen.
Lee suspected that the ash from the Cretaceous volcanoes might have caused a similar effect, because most of the original phosphorus, iron, and silica from the original volcano ash were missing in the rocks that his team found in Texas.
“We found the amount of phosphorus entering the ocean from this volcanic ash was about 10 times more than all the phosphorus entering all the world’s oceans today. That would have been enough to feed an oxygen-depleted dead zone where carbon could be exported all the way down to the sediment,” Lee noted.
“To generate a hydrocarbon deposit of economic value, you have to concentrate it,” Lee said. “In this case, it got concentrated because the ashes drove that biological productivity, and that’s where the organic carbon got funneled in.”
While the study examined Cretaceous rocks from the Eagle Ford and the Austin Chalk, and focused on that particular period in North America, Lee suggests that the Marcellus in Pennsylvania that was laid down much earlier—more than 400 million years ago in the Ordovician period—could also be associated with ashes. It’s also possible that the Vaca Muerta shale play in Argentina may have been formed with the help of arc volcano ash.
“The Vaca Muerta field in Argentina is the same age and was behind the same arc as what we were studying,” Lee said.
Shale oil and gas are not found in the ash layers, but appear to be associated with them, according to Lee. Related: OPEC Deal In Jeopardy As Iran And Saudi Arabia Square Off
Those ash layers are also so thin that they don’t show on the seismic scans of the oil drillers. But the suggestion that hundreds of closely spaced ash layers could be a tell-tale sign that there are unconventional oil and gas resources in the rocks “might allow industry geologists to look for bulk properties of ash layers that would show up on scans,” according to the scientist.
While volcano ash may have helped the formation of the U.S. shale plays some 100 million years ago, fracking technologies have helped U.S. drillers to extract those tight oil and shale gas resources in recent years.
The largest shale plays in the United States are expected to pump a total of 6.823 million bpd of oil this month, and the volume will rise to 6.954 million bpd in April, with Texas plays the Permian and Eagle Ford leading the production growth, EIA estimates show.
Total U.S. oil production has already surpassed that of OPEC’s leading producer Saudi Arabia, and the United States is on track to topple Russia to become the world’s largest crude oil producer as early as later this year.
By Tsvetana Paraskova for Oilprice.com
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