Nevada has produced nearly 50 million barrels of oil, but that is just a drop in the bucket compared to the potential buried in the Nevada portion of the Sevier thrust belt that spans the length of the Rocky Mountains and has been prolific in Wyoming and Utah.
So why have companies never tapped this potential resource?
According to one geologist who has been studying Nevada for years, it is a combination of geology and conventional wisdom based on inaccurate maps.
In today’s world of high tech exploration tools, Alan Chamberlain, a geologist and partner in Cedar Strat Corp. of Las Vegas, is going back to the basics to make his case on Nevada’s potential. He has spent years doing surface geology and developing maps of the state’s complicated geology, and he says the traditional thinking about Nevada is inaccurate and masks an impressive exploration province.
"Nevada has never had a geological survey, so a comprehensive geological survey of the mineral potential of the state has never been done," Chamberlain said. "Consequently, there are a lot of theories about the Great Basin out there, but few are based on real geologic legwork.
"When I and just about every other geologist was in school we were taught that the Great Basin is a bunch of horst and grabens," he said. "That conventional wisdom has led exploration efforts to focus on the grabens or valleys in Nevada, and that’s where all the discoveries have been made."
According to Chamberlain, Shell's 1954 oil discovery under the Tertiary unconformity in Railroad Valley appeared to confirm the conventional theories, so exploration activities over the years have tried to repeat that success. Several additional fields were found, with the largest discovery the Grant Canyon Field, which has produced about 20 million barrels of oil from essentially two wells since the early 1980s.
"Despite these discoveries, Nevada was never comprehensively mapped," he said. "In the 1970s the U.S. Geological Survey authorized some geologists to make quick and dirty geologic maps of Nevada’s counties, but that effort was quite limited."
For example, in Lincoln County, which covers 10,000 square miles, the agency assigned two geologists and gave them one year to map the entire county.
"One geologist noted in his report that he just arbitrarily mapped the geology between mining districts," Chamberlain said. "That is still the only published map for White Pine County."
Testing the Theory
Chamberlain, who presented a paper on Nevada potential during the recent AAPG Mid-Continent Section meeting in Tulsa, got involved in Nevada when he was with Placid Oil in the 1980s and stumbled onto Shell’s huge stratigraphic database on the state.
"Back in the 1950s and '60s Shell had teams of geologists go out and measure all the rocks in Nevada and western Utah -- a $200 million effort," he said. "I was able to meet a lot of those guys in the early 1980s and revisit those old Shell sections."
Chamberlain came up with the idea of running a gamma ray log over these measured sections that made them look like well data.
"This real rock data helped evolve a new geologic model of Nevada," he said.
He really jumped into the mysteries of Nevada geology while researching his dissertation.
"As part of that research I came down toward southern Nevada, where the Colorado River had dug out enough of the Paleozoic rocks to see into the bedrocks," he said. "I could see there weren’t the series of horsts and grabens like we had been taught, but that the area was in fact part of the foldbelt running all the way down the Cordillera from Alaska to South America.
"When you think about it," he added, "it seems unlikely that the thrust faults from the foldbelt would be present in Canada, Montana, Idaho and Wyoming, disappear in Nevada and then reappear in Texas."
Chamberlain believes remigrated hydrocarbons trapped below a blanket of Tertiary volcanic rocks strongly suggest that huge fault folds in the Nevada portion of the Sevier thrust belt contain significant volumes of oil and gas.
"About a quarter of the earth’s known reserves of oil and gas are found in thrust belts," he said. "Surface oil seeps commonly occur in thrust belts charged with oil and gas, such as the Wyoming-Utah portion of the Late Cretaceous Sevier thrust belt.
"However, oil seeps in the Nevada portion of the thrust belt have been trapped by a blanket of Tertiary volcanic rocks," he said. "After trapping the remigrated oil for 30 or 40 million years, some buried Nevada oil seeps became commercial. All the commercially produced oil in the state has come from those seeps."
But worldwide, when there are oil seeps at the surface, companies drill down into the thrust duplexes to uncover oil and gas.
"Because there was no concentrated geologic mapping done in Nevada, people traditionally misinterpreted eastern Nevada and believed it was a series of horst and grabens rather than thrust duplexes," he said.
"As a result, nobody has tested the thrust duplex system -- and that is where a new play could emerge in the state."
Chamberlain said he presented his thrust belt model to Exxon in the mid-1980s and the firm shot approximately $75 million of seismic data.
"Exxon was the only company that shot regional lines to look for thrusting," he said. "They shot over the mountains and valleys, which was significant, because the only other seismic in Nevada was in the valleys only. At that time Exxon was excited by what they saw and drilled the Aspen exploration well, which went from Devonian back into Mississippian, confirming the thrust model."
However, at that time the company cut its American frontier projects and did not pursue the project.
"I think Exxon was right on the mark," he said, "and would have found some big oil if they had stayed a little longer."
Another well 20 miles north of Las Vegas, drilled by Grace Petroleum in the footwall of the Gas Peaks thrust, also verified the thrust model, according to Chamberlain.
"The company drilled through a normal section down to the Cambrian, and at about 7,000 feet went from the Cambrian back into Triassic and then drilled a normal section down to 18,000 feet," he said.
Over the past several years Chamberlain has identified 36 large structural features.
"I have 36 plays, and each one has five to 10 prospects in it," he said. "By taking the porosity of each pay zone and calculating that over the area of each prospect, I estimate each one has more than one billion barrels of oil.
"These are huge structures," he continued. "We are looking at the same karsted, Middle Devonian reservoir rocks that produce at Grant Canyon, where one well flowed over 15 million barrels of oil. If you take the 400-foot karsted interval that produces at Grant Canyon and put it in one of these big fault folds, there is huge potential."
He said he has sold one prospect about 20 miles south of Elko to a large independent, which likely will drill a well in 2004.
Another independent drilled a well a year ago near Railroad Valley based on Chamberlain’s leads. He said the well was about five miles off structure and the firm may drill a second well next year.
Of course, not everyone shares Chamberlain’s enthusiasm regarding Nevada’s potential, including the USGS, based on its 1995 hydrocarbon assessment of the state.
USGS spokesman Chris Schenk said the survey will be reassessing the state in coming months, but he did not anticipate much change in the numbers.
"We haven’t seen any activity that would likely change our past conclusions," he said.
Still, Chamberlain remains confident and optimistic.
"The land in Nevada today is wide open -- I can buy huge tracks for a song," he said. "For one independent we tied up 400,000 acres of contiguous leases for $1.50 per acre. You can’t do that anywhere else."
But when that first big discovery is made that will change overnight, he warns.
"If we can find one billion-barrel field on this thrust belt it will create an oil rush," he said. "I hope to be right in the middle of it."