Monte Mountain thrust sheet
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.
 LANDSAT
image of Railroad Valley
"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."
Mobile GPS combines work and play
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.
 Chevron
Folds in the Oquirrh Mountains in Utah
"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."
'Huge Structures'
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.
 Aerial
view of the Keystone thurst
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."
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