debate about cooking up hydrocarbons keeps getting hotter.
Some scientists insist that all petroleum comes from
abiogenic processes, with hydrocarbon development occurring in the
Most geochemists and petroleum geologists remain
convinced that crude oil and natural gas have organic origins.
Look for this dispute to intensify in 2003, with
new heat coming from an unexpected venue. In June, AAPG's typically
sleepy Hedberg Conference could be the spark that sets off scientific
Hedberg conferences address topics proposed by AAPG's
Research Committee. They take place in informal settings, with attendance
limited to 80-100 persons.
On June 9-12, however, a Hedberg
Conference will be held in London with the theme "Origin of
Petroleum — Biogenic and/or Abiogenic and Its Significance in Hydrocarbon
Exploration and Production."
"The timing is right," said Barry Katz, a ChevronTexaco
Fellow in Houston and a member of the conference's program committee.
"Historically, what has been the big issue is that there's essentially
a Western and an Eastern school of thought.
"On the Western side, we've gone through what you've
typically done in the scientific method," he noted. "The Russian
arguments have been just that, arguments. We have yet to get them
in a room to see what they have on the table."
Katz said he hopes the leading theorists from both
sides will attend, so "we can have a balanced view and get everybody
to talk to each other. That's what the Hedberg conferences are all
Is It Commercial?
An explorationist might dismiss the entire controversy
over petroleum origination, except for two key points:
- Theorists of abiogenic petroleum tend to see hydrocarbons as
not just abundant but super-abundant, with no possibility of constrained
- Petroleum generated by abiogenic processes could occur anywhere,
so exploration need not be limited to sedimentary basins, or to
depths of only a few miles.
Modern theory directly links petroleum origination
to organic detritus, according to Michael Lewan, a research geochemist
for the U.S. Geological Survey in Denver.
"The modern, organic theory of the origin of petroleum
states that a portion of the lipid fraction of micro-organisms deposited
in anaerobic sediments is the original source of petroleum," he
Proteins and carbohydrates make up 85-95 percent
of the weight of these micro-organisms, and are rapidly degraded
by microbial activity, Lewan said.
The remaining 5-15 percent can be preserved in anaerobic
sediments, representing "unique depositional conditions that result
in organic-rich, sedimentary-rock intervals in some stratigraphic
sequences," he explained.
Lipid material preserved in the original sediments
polymerizes into kerogen, an insoluble organic material, Lewan said.
"As these organic-rich rock intervals are heated
with burial in sedimentary basins, the hydrocarbon polymers within
the kerogen thermally crack through a free-radical mechanism to
yield liquid and gaseous petroleum hydrocarbons," he said.
Research in the lab and in the field demonstrates
that petroleum development can and does take place in the earth's
crust, he stated.
"I feel we've done a very good job of simulating
production of petroleum in the laboratory," Lewan said. "Between
the lab work and the fieldwork, we've put together a very good picture."
Although hydrocarbons can be produced from inorganic
sources, a 1993 study based on helium isotopes found that abiogenic
hydrocarbons account for less than 200 parts per million of cumulative
global production to date, Lewan said.
"Is it so diffuse that it never really accumulates?
Is it focused in certain areas where it can be accumulated?" he
"I don't think anybody has ever doubted that there
is an inorganic source of hydrocarbons. The key question is, 'Do
they exist in commercial quantities?'"
From Russia, With Love
Various other theories oppose the organic-origin explanation.
The principal counter-theory is often called the abyssal, abiotic
Russian-Ukrainian theory of petroleum.
In 1951, a group of Russian scientists issued a challenge
to the theory of organic petroleum origination. They claimed that
hydrocarbons are produced from inorganic materials, at upper-mantle
to lower-crust depths.
New controversy over that proposal resulted from
a paper published in August 2002 in the Proceedings of the National
Academy of Sciences (U.S.), "The evolution of multi-component systems
at high pressures: IV. The thermodynamic stability of the hydrogen-carbon
system: The genesis of hydrocarbons and the origin of petroleum."
This paper, written by J.F. Kenney of Gas Resources
Corp. in Houston and three Russian co-authors, rejects the proposal
that petroleum can derive from "highly oxidized biotic molecules
of low chemical potential."
Drawing on scaled particle theory and simplified
perturbed hard-chain theory, Kenney et al. present an evaluation
of the chemical potentials and related thermodynamic affinities
for n-alkanes. They conclude:
"The H-C system does not spontaneously evolve heavy
hydrocarbons at pressures less than about 30 kbar, even in the most
favorable thermodynamic environment. The H-C system evolves hydrocarbons
under pressures found in the mantle of the Earth and at temperatures
consistent with that environment."
They also briefly describe the experimental production
of petroleum hydrocarbons using only wetted marble (CaCO3)
and solid iron oxide (FeO), in an apparatus allowing investigation
at pressures up to 50 kbar and temperatures up to 1,500° Celsius.
Kenney said there is no real debate about petroleum
"There has not been any 'debate' about the origin
of hydrocarbons for over a century," he stated. "Competent physicists,
chemists, chemical engineers and men knowledgeable of thermodynamics
have known that natural petroleum does not evolve from biological
material since the last quarter of the 19th century."
In their paper, Kenny et al. contrast the H-C system
with the H-C-O system, "which manifests consistently decreasing
chemical potentials with increasing polymerization."
They then discuss reactions involving C6H12O6,
or glucose, as a "typical biotic reagent." In response, Lewan noted
that neither carbohydrates nor proteins are now thought to have
a part in petroleum formation.
"Significant scientific advances over the last 40
years have tested, modified and refined the organic theory for petroleum
formation in the Earth's crust," Lewan said.
"It is unfortunate that Kenney et al. have chosen
to ignore these efforts of other competent scientists, and elevate
their inorganic theory on the misconception that the organic theory
is based on carbohydrates being the source of petroleum."
The Golden Touch
No one in the United States has been more associated
with the theory of abiogenic petroleum than Thomas Gold, a professor
of astronomy at Cornell University, now retired.
"The only real opponents to this story (of abiogenic
origin) are in Western Europe and in the United States, and they
are the professional petroleum geologists," he said.
"The subject of organic chemistry was wrongly taken
by petroleum geologists long ago to mean chemistry of biologic origins.
You can still have a book of organic chemistry that has nothing
to do with organisms at all."
Gold most recently explained his theories of the
origin of petroleum in his 1999 book The Deep Hot Biosphere, which
presents the view that life on Earth exists to a depth of many miles.
That helps him explain the apparent organic constituents
of petroleum. In Gold's view, hydrocarbons form at a depth of 100
to 300 kilometers and take on some organic attributes as they migrate
"Oil is a very good nutrient for microbiology. In
1972, I began to realize that the oil had soaked up biological molecules
that the petroleum itself had fed," he said.
Migration also explains another commonly offered
piece of evidence for organic petroleum, depletion of the carbon
13C isotope, according to Gold.
Photosynthesis and other organic activity favor the
stable 12C isotope over the stable 13C isotope.
The resulting 13C deficiency is taken as an indicator
of organic processes.
Petroleum shows the 13C depletion to an
even greater degree than its supposed organic source matter, but
in a ratio similar to that of the lipid fractions of those organisms.
Gold theorizes that carbon-bearing molecules diffusing
through a porous mass, in any process, results in fractionation
that favors the lighter 13C isotope.
"Biology is not a nuclear reactor. It can't make
carbon-13 or carbon-12. But it's treated in the literature that
the 12C-13C preference is strictly a plant
matter," Gold said. "It's quite clear that there is an isotopic
fractionation occurring in the migration path."
More evidence of upward hydrocarbon migration from
great depth comes from the prevalent occurrence of helium with petroleum,
"We have two conflicting pieces of evidence. Petroleum
contains helium, which the plants cannot have concentrated," he
said. "Petroleum also contains purely biological molecules, which
petroleum-fed biology deep in the ground could concentrate.
"This (upward migration from great depth) is the
only explanation I've ever heard of to account for the amount of
helium brought up with petroleum."
Petroleum explorationists have good reason to care
about the true origin of hydrocarbons, Gold noted.
"For one thing, they always avoid drilling into the
basement rock," he said. "They've probably avoided drilling into
a large amount of very productive rock."
Also, in Gold's theory hydrocarbons continue to well
up from the mantle. He believes depleted petroleum reservoirs are
refilling, all over the world.
Seeing Is Believing?
A new perspective on isotopic analysis of abiogenic
hydrocarbons appeared in a letter to Nature magazine in April 2002,
"Abiogenic formation of alkanes in the Earth's crust as a minor
source for global hydrocarbon reservoirs."
Barbara Sherwood Lollar and four co-authors from
the Stable Isotope Laboratory at the University of Toronto reported
their analysis of gas from the Kidd Creek mine in Ontario, typical
of hard rock mines operating throughout the Canadian Shield.
"These gases had been known historically in the mines
for a very long period, up to 100 years, but nobody had investigated
them until the 1980s. In Precambrian rock, it's not intuitively
obvious where these hydrocarbons come from," said Sherwood Lollar,
a professor of geology at the university.
According to the authors, the Kid Creek gases were
composed of methane, ethane, H2 and N2, with
minor concentrations of helium, propane and butane.
"We knew that these were unusual in composition.
They don't look like thermogenic. They don't look like microbial,"
Sherwood Lollar said.
An unusual pattern of d13C values among
C1-C4 alkanes provided evidence of abiogenic
formation. Additional support came from study of d2H
"The inverse relationship of 13C isotope
depletion and2H isotope enrichment between C1
and C2 for the Kidd Creek samples supports a polymerization
reaction as the first step in the creation" of higher hydrocarbons,
the authors concluded.
Because the isotopic signature differed markedly
from that of thermogenic or bacteriogenic hydrocarbons, Sherwood
Lollar theorized an origin in water-rock interactions.
"The gases are found intimately associated with these
saline groundwaters and brines, with up to 10 times the saline content
of oceans," she said.
Identification of the 13C-2H
inverse relationship in abiogenic gas allowed comparison with isotopic
ratios in commercial gas reservoirs. The study found no meaningful
presence of abiogenic hydrocarbons in commercial natural gas production.
"Based on the isotopic characteristics of abiogenic
gases identified in this study, the ubiquitous positive correlation
of d13C and d2H values for C1-C4
hydrocarbons in economic reservoirs worldwide is not consistent
with any significant contribution from abiogenic gas," the authors
"The key point is that abiogenic hydrocarbons have
been talked about for a long time, but until now we didn't have
a very good constraint on what they looked like," Sherwood Lollar
Katz said Western science recognizes that abiogenic
hydrocarbons can result from natural processes, including the possibility
of hydrocarbons originating at great depth.
"I don't think anybody's arguing that gas couldn't
be generated from the mantle," he said.
However, even the Russian scientists he has worked
with accept the organic origin of petroleum found in large, commercial
"I've worked with geochemists and basin modelers
at what was the Soviet Union's Institute for Foreign Geologic Studies.
They were working with the same concepts we were," he said.
If abiogenic petroleum exists in amounts large enough
for economic production, he hopes details of the science involved
will be presented at the London Hedberg .
"I have yet to have anyone show me that there are
commercial quantities of these hydrocarbons," Katz said.
"I'm a scientist, so I have to keep an open mind.
But I need to see some evidence."