July, Mike Lewan had an unusual conversation with his new neighbor, who had
been reading lately about oil from deep sources that cant be explained.
Lewan, though slightly amused, was not entirely surprised to hear this topic
in casual conversation.
In the 1980s, Thomas Gold, an astronomer at Cornell University, received support from the Swedish government to drill into the Siljan Ring, the site of an ancient meteorite crater in central Sweden (shown here), in search of inorganic oil from Earths mantle. Gold believed that natural gas migrates upward from the mantle where it transforms into more complex gases and oil, and that the petroleum could be expelled through large releases of energy such as a meteor impact. The experiment, which did not find large quantities of such gas, still helped mobilize a small community of scientists who reject the theory of organic origins of petroleum. Image copyright Tom Johansson.
A petroleum geochemist at the U.S. Geological Survey, Lewan is an expert on the origins of oil, and quite familiar with an idea that has been lingering within some scientific circles for many years now: that petroleum oil and natural gas comes from processes deep in Earth that do not involve organic material. This idea runs contrary to the theory that has driven modern oil exploration: that petroleum comes from the heating of organic material over time in Earths shallower crust.
The so-called inorganic or abiogenic oil idea has been getting more attention lately, at a time when it seems that energy is on everyones mind. With oil more expensive than ever and many people citing future shortages, understanding the origins of petroleum is increasingly relevant.
For the first time ever in North America, proponents of the inorganic origins hypothesis, largely from Russia and the Ukraine, had a major forum for their ideas at a meeting held in June in Calgary, Alberta a city that has built its wealth on the vast petroleum deposits found in the Canadian province. Held in association with the annual meeting of the American Association of Petroleum Geologists a group of people whose livelihood depends on understanding how and where oil and gas form this was no ordinary forum.
Walking around the modest-sized ballroom in the Calgary Hyatt right before the meeting started, words like lunatic and crazy were being tossed between some participants. Other attendants had a giddy glow of excitement, rarely seen at such gatherings. A co-convener of the meeting, Barry Katz, who is a petroleum geologist at Chevron, hesitantly mentioned that before it even began, the meeting was receiving attention from the Financial Times, as well as publications as unlikely as Playboy yes, Playboy.
One thing is for sure, Katz says: Scientists from the minority inorganic oil camp, promoting myriad ideas and lacking a unified hypothesis, have a way to go if they want to overturn the theory of organic petroleum genesis. Although most scientists agree that inorganic petroleum exists, he says, they differ widely in their thoughts on how it forms and how widespread it is versus organic petroleum. The meeting was a vehicle to share these ideas and it highlighted what geologists know and dont know about the origins of one of the most important resources on Earth.
Starting in the 1860s, scientists in Scotland found a way to make oil: They took rocks known as oil shales, which contain solid organic material called kerogen, and heated them to break down the kerogen and produce gas and oil. Using this process, Scotland stayed profitable and competitive with the petroleum industry until 1960, Lewan says.
Indeed, the idea that heated organic material results in petroleum, so-called fossil fuels, has been around for hundreds if not thousands of years. In 1757, Russian scientist M.V. Lomonosov wrote: Rock oil originates as tiny bodies of animals buried in the sediments which, under the influence of increased temperature and pressure acting during an unimaginably long period of time, transform into rock oil.
By the mid-20th century, the organic model was widespread, given a big boost by modern chemistry, paleontology and geology. Katz points to a 1936 paper by Alfred Treibs, in which he showed that chemical compounds in oil called porphyrins have the same chemical structure as chlorophyll, thus linking petroleum to plant material.
Over subsequent years, researchers would find evidence of other chemical signatures present in petroleum that correspond to precursors of life. These biomarkers are essentially molecular fossils, and they differ between hydrocarbons, Katz says. Oil tends to come from material that is largely from an algal source, although not exclusively, and gas tends to come from material that is more woody material.
Hydrothermal fluids exude vigorously from the Lost City system, located 15 kilometers away from the spine of the Mid-Atlantic Ridge. Here, minerals precipitate from the fluids and create white feathery spires and mounds of carbonate. Scientists believe that the vented gases are from the mantle and are abiogenic (not made from life) in origin, and some researchers are looking for terrestrial analogs to such systems to find untapped gas and oil resources. Courtesy of University of Washington.
In explaining biomarker evidence at the Calgary meeting, Marcio R. Mello of High Resolution Technology & Petroleum in Rio de Janeiro, Brazil, compared different types of petroleum to different types of people, and biomarkers to DNA. Who is the mother? he said jokingly.
To answer that question, geologists have linked biological molecules found in petroleum of a certain age to precursors of specific life forms found in ancient environments of the same age. For example, oleanane, a compound that led to the evolution of flowering plants, is present in Tertiary and Upper Cretaceous rocks and oil. Mello said that geologists have also linked biomarkers to the specific environments in which they formed.
In addition to biomarker evidence, work done by the oil industry in the last 25 years has defined the petroleum systems concept, linking where petroleum is found to where it originates. Wallace Dow, now a consultant based in The Woodlands, Texas, recalled his days as a geologist at Amoco in 1970, when he and others studied the Williston Basin along the eastern edge of the Rocky Mountains to nail down the geographic and geologic trends in sedimentary basins, where most petroleum is found. They tested and analyzed 22 oils and, based on chemical composition, defined three oil types. To find out where those oils came from, the researchers analyzed core samples in the basin and found three distinct organic-rich intervals of rock, or source rocks, where the petroleum originated. This work was some of the first to link oil accumulations to their source rocks.
Not long after that study, in 1978, Lewan and colleagues sought to replicate oil generation and expulsion in the lab. The team took some crushed shale containing organic matter, placed it in a 1-liter reactor and added enough water to submerge the rock. After heating the material between 300 and 360 degrees Celsius for several days, there was beautiful oil floating on top of the water, Lewan says.
In nature, however, oil does not form at such high temperatures, and it forms over thousands to millions of years. Thus in the experiment, the higher temperatures compensated for the short timeframe. The extrapolation works very well, substituting temperature for time, Lewan says, and the researchers have successfully entered the back calculations into basin models to determine timing and depths of petroleum generation.
Inorganic oil supporters, however, point to these experiments as a weakness in the model, saying that no one has ever successfully produced organic oil in the lab without a lab time machine accounting for the higher temperature (which according to the organic model would take thousands to millions of years). Thats in part why the inorganic camp follows a different model for oil formation: Instead of breaking down kerogen at high temperatures into lighter gases and oil, they think that hydrocarbons start off as simple compounds and then chain up the ladder through a cooling process deeper in the planet.
In the 1980s, Cornell University astronomer Thomas Gold made headlines with a variation on this idea, saying that methane (a common natural gas) migrates upward from the mantle where it transforms into more complex hydrocarbons and then accumulates in igneous rocks. Biomarkers, he said, are from microorganisms interacting with the petroleum along its migration route. The way to tap this source, he said, would be through a cataclysmic release of energy that would propagate through the mantle, releasing the petroleum.
Thus, Gold, with the support of the Swedish government in the 1980s, drilled two deep wells into the Siljan Ring, the site of an ancient meteorite crater. They did find some gas, but researchers have varied widely in their interpretation of the results. While Gold heralded the find as proof of abiogenic petroleum, most geologists dismissed the findings as too small to be economically viable.
Gold died last year, but a small and persistent group of scientists still passionately promotes the idea that petroleum originates from a deep, inorganic source.
Signatures for Mars
At the June meeting in Calgary, the debate was fierce. Katz says, however, that there was just as much, if not more, infighting among the inorganic folks than between them and the organic petroleum proponents. Thats because the ideas on how petroleum forms inorganically vary widely from oil present as inclusions in rocks at depth to gases forming in a setting analogous to hydrothermal vents on the seafloor.
Alexander Kitchka, a co-convener of the meeting and a geologist at the National Academy of Sciences in the Ukraine, attributes the various ideas to the fact that it is a live, developing theory. He says that outside North America (where people prefer the fast-food bio-organic paradigm), scientists are working on hybrid ideas that combine mantle-derived hydrogen with biologically derived carbon to explain the origins of oil.
T.C. Onstott, a geomicrobiologist at Princeton University, samples a borehole from a mine site in northern Canada for both gases and groundwater, to determine whether the microbes in the groundwater might be living off of inorganically derived gases (hydrogen or methane) as their source for life. The work, funded through the NASA Astrobiology Institute, could ultimately help researchers determine whether there is life on Mars and other planetary bodies. Courtesy of Barbara Sherwood Lollar.
Alexei Milkov, however, a Russian petroleum geologist with BP in Houston, Texas, who was educated in Russia, does not think of the debate as East versus West, noting that the organic theory is taught at universities, is practiced at major research institutes that work on the fundamental problems of petroleum geology, and is applied by companies exploring for and producing oil and gas. The success of Russian petroleum exploration, he says, did not come from the inorganic model. He adds that the subject of petroleums origins is more widely discussed in the former Soviet Union than elsewhere. When I talk with practicing Russian geologists, they often ask my views on the abiogenic origin of petroleum, Milkov says. This never happens in the United States, where organic is accepted fully and without scientific questioning.
The actual question, says Barbara Sherwood Lollar, director of the Stable Isotope Laboratory at the University of Toronto, is not whether abiogenic hydrocarbons exist but whether they occur in the natural environment. Abiogenic gases are a clear fact, she says. I can make them on the lab bench today, with basic chemical reactions.
Indeed, last year, a team of researchers led by Henry Scott of Indiana University at South Bend created methane in the lab at temperatures and pressures common in the mantle. The results show that methane could be stable as deep as 100 kilometers below Earths surface.
Lewan has read these studies with interest, and says that while Scotts teams work is elegant, it does not represent the mantle as scientists currently know it, pointing to the fact that the experiment used calcite, a mineral not found commonly in the mantle. People can make abiogenic gas, but whether the results can be applied to the Earths mantle or deep crust remains to be seen, he says.
Abiogenic gas in the crust, however, has been discovered. Working at the Kidd Creek Mine in Ontario, Sherwood Lollar and colleagues analyzed gases found there and determined they were inorganic. Using both carbon and hydrogen isotopes, they identified a unique inorganic chemical signature that differs from the signatures of gases in economic accumulations, as published in Nature in 2002. To date, nobodys been able to show that same signature in any of the economic deposits, Sherwood Lollar says. That would argue that any of the economic deposits weve found to date are in fact quite consistent with biological origins. Still, she says, the work shows that inorganic gas is a real phenomenon.
Her work, which is partially funded through NASA, has continued at other similar sites in Canada and Africa, showing that such inorganic gas formation is common in Precambrian shield systems that date back more than 3 billion years. NASA is interested because the work could provide a test for whether methane and other hydrocarbons found off Earth are either made by microorganisms or acting as a source for life, as occurs at mid-ocean ridges, Sherwood Lollar says. On Mars, for example, scientists have detected methane, but do not know its origins.
Sherwood Lollars team has found three different isotopic signatures in natural gas on Earth: organic, inorganic and a mixture of the two. The mixed signal, she says, comes from microbes using up hydrogen in these Precambrian systems and making their own methane, which then mingles with the inorganic methane. Analyzing the methane on Mars using the teams isotopic method could indicate whether life exists on that planet.
This work, which is currently in press in Chemical Geology, could also be important in the ongoing debate about the origins of petroleum on Earth. Heres a signature we can use to actually look at some of these deposits that have been claimed by Thomas Gold and others to be abiogenic in origin and see whether it fits, Sherwood Lollar says.
Back in the 1980s when Gold drilled the Siljan crater and in the 1970s when the Russians began massive drilling into the Kola Peninsula in search of inorganic petroleum, the technology was not available to look at hydrogen isotopes. The limited carbon isotope data, Sherwood Lollar says, was not enough to prove or disprove the origins of any gas that was discovered, which in both cases, she adds, was present in miniscule amounts.
Now, Sherwood Lollar says, scientists are shifting away from the very expensive one-shot, one-location superholes to an attempt to take advantage of any windows into the subsurface that are already available to us. That is leading researchers to two key areas: mining environments and oceanic vent systems.
Stanley Keith has been reading with interest in recent years about odd ecosystems that thrive at mid-ocean ridges. One that has especially caught his eye is a hydrothermal system, 15 kilometers away from the Mid-Atlantic Ridge, called the Lost City. There, magnificent white towers of minerals are home to bacteria and inorganic methane. Below this vent system, rocks from the mantle react with seawater in a series of reactions called serpentinization, producing the natural gas that is vented at the top for the microorganisms to consume.
Keith, a mineral geologist who owns a consulting company called MagmaChem in Sonoita, Ariz., began thinking that perhaps he could find ancient systems below the continents that were analogs to this oceanic system. If so, the hydrothermal environment would also create inorganic methane, and perhaps other hydrocarbons, terrestrially. The geologic challenge is to figure out to what extent serpentinization creates this kind of opportunity beneath basins in continental settings, he says.
According to his model, large slabs of oceanic crust that have pushed below the continents contain hydrothermal brine that reacts with the mantle rocks to form methane and hydrogen. As the gases move through the system, they cool and transform to more complex hydrocarbons, ultimately landing in sedimentary basins and other spots around the world. Keith sees his model as bridging the gap between the observations of the organic model with known processes that occur in the mantle. People have recognized the trap configurations in basin geology for a long time, Keith says. Were not throwing the biogenic model out; were simply building it into what were doing.
Like Gold, Keith suggests that biomarkers are the result of microbes interacting with the inorganic petroleum during its migration up into the crust. The biosphere has been coexisting with the petroleum system throughout geologic history, Keith says. But, Golds petroleum model missed something called geology. That was always its weak point, and what led to such divisions in the inorganic/organic oil debate, he says.
Keith is drawing on processes that no one would argue with, Sherwood Lollar says. Scientists have known about serpentinization for 30 years, she says, and its always been known that it can produce hydrogen and methane as a byproduct. She also says that the idea that microbes are using the inorganic gases has been well-understood the past 10 years. But when it comes to the broader implications of mantle-derived hydrocarbons, the jurys still very much out, Sherwood Lollar says, as there is no consensus on the phase in which the gas would move through the mantle.
In her own work, looking at the only sites in the continental crust where abiogenic gases have been identified, Sherwood Lollar says that there is no mantle component; the methane instead comes from water and rock interactions, including serpentinization in the crust. The rock is in contact with water in fracture systems, and in these old rocks, they sit in contact for millions and millions of years, she says, until you get major alteration of the rock and of the water because of that exchange. Still, Sherwood Lollar says that any mantle-derived gases would be abiogenic, and so it might come down to testing Keiths model using the isotopic signatures her team has identified.
Keith recently found what he calls uncontestable exposures in the field near Elko, Nev., that support the idea that hydrocarbon formations there are the tops of giant seep systems above big hydrothermal systems. The outcrops, he says, show physical evidence of a fossilized hydrothermal system that was active in the Eocene about 40 million years ago.
Its just spectacular stuff, Keith says. Its the first evidence like this in a continental setting, and we can defend it. He and his colleagues plan to publish the work, which is being funded through a client interested in economic development of the field.
Lewan says that he looks forward to seeing a write-up of the work in peer-reviewed journals he sees the work Keith presented at the June meeting as being far from complete. The proposed hydrocarbon-charged plume is never described in terms of its phase or the driving force responsible for its ascent, he says.
Once again, no one doubts that inorganic hydrocarbons may occur in association with hydrothermal systems, Lewan says. The real issue is that they do not appear to be a significant contributor to the economic accumulations currently under production.
Dollars and sense
In my lifetime, there have been two main trends that Ive observed: the big debate with Gold in the early 1980s and then this one, and those sort of correlate with times when petroleum is getting expensive, Lewan says. Whether thats actually a cause and an effect remains to be determined, but it seems like this keeps coming up periodically.
And at the end of the Calgary meeting, one thing was clear: The debate is far from over. In the meantime, though, both groups say they can learn from one another.
For example, although Katz says that he was not persuaded by any evidence on the inorganic side, he points to studies that have been done to explore inorganic petroleum that have contributed to his knowledge base. For example, scientists have studied gas accumulations found with odd isotopic compositions, thought to indicate an inorganic origin. But, he says, so far, they have mostly found evidence for gas alteration, something quite useful in searching for oil. If the gas is being degraded in some fashion, that has implications on how much gas is there or the type of gas that might be there.
Our story is not complete, Katz says. I know a lot more now than I did when I started 26 years ago, and I hope that when I retire, Ill know more then than I know now. Still, he says, I think we have the concepts down from an organic standpoint.
The challenges Katz sees now to petroleum exploration are political issues of access and economic. Oil is not simple to find and its very expensive to produce, and the places that were going now are more difficult and more expensive than ever, he says. It is a finite resource, so dont waste it. As for inorganic petroleum, I dont see any evidence for that, Katz says.
Keith, however, remains optimistic. If his model is correct, he says, weve barely tapped, from the exploration point of view, the hydrocarbon potential thats out there on this planet. He looks forward to taking geologists to the outcrops hes discovered in Nevada and, over time, sees the two sides coming together. That process will take decades, Keith says, and will require a new way to explore for oil and natural gas.
The key word, though, that Katz and Lewan both emphasize is economic. Both acknowledge the existence of abiogenic petroleum and say that it might be an untapped source, but that it is likely present in small quantities only. The organic origin of petroleum is a theory based on field observations, laboratory experiments and basin models; it explains currently known economic occurrences of natural gas, crude oil and asphalt, Lewan says. The inorganic origin remains a hypothesis; it has not been proven to be a significant contributor to currently known economic petroleum accumulations.
Indeed, Sherwood Lollar says, a really exciting new idea needs to have a very high standard of proof. She is grateful, though, to the Thomas Golds of the world who throw out grand ideas and get people thinking in new directions. In the end, however, she says that the scientific method is the final arbiter.