In an era of rising oil and gas prices, the possibility that there are
untapped reserves is enticing. Since the first U.S. oil well hit pay dirt
in 1859, commercially viable wells of oil and gas commonly have been
drilled no deeper than 3 to 5 miles into Earth’s crust. “These
experiments point to the possibility of an inorganic source of
hydrocarbons at great depth in the Earth-that is, hydrocarbons that come
from simple reactions between water and rock and not just from the
decomposition of living organisms,” stated Dr. Russell Hemley of the
Carnegie Institution’s Geophysical Laboratory, and co-author of a study
published in the September 13-17, early, on-line edition of the
Proceedings of the National Academy of Sciences.
Methane is the most abundant hydrocarbon in the Earth’s crust and it is
the main component of natural gas. Often, gas reserves are accompanied by
liquid petroleum. However these reserves, at 3 to 5 miles beneath the
surface, exist in relatively low-pressure conditions. Whether
hydrocarbons exist deeper-and could even be formed from non-biological
matter-has been the subject of much debate. As depth increases in the
Earth, the pressures can become so crushing that molecules are squeezed
into new forms and the temperature conditions are like an inferno making
matter behave much differently. The team of scientists performed a series
of experiments at Carnegie, the Carnegie-managed High Pressure
Collaborative Access Team (HPCAT) at Argonne National Laboratory, and at
Indiana University South Bend-together with calculations performed at
Lawrence Livermore National Laboratory-to mimic conditions that occur in
Earth’s upper mantle, which underlies the crust at depths of about 12 to
37 miles (20 to 60 km) beneath the continents.
With a diamond anvil cell, the scientists squeezed materials common at
Earth’s surface–iron oxide (FeO), calcite (CaCO3) and water–to pressures
ranging from 50,000 to 110,000 times the pressure at sea level (5 to 11
gigapascals). They heated the samples using two techniques-focused laser
light and the so-called resistive heating method-to temperatures up to
2,700 degrees F (1500 degrees C). The researchers found that methane
formed by reducing the carbon in calcite over a wide range of temperatures
and pressures. The best conditions were at temperatures and pressures of
about 1000 degrees F and less than 70,000 times atmospheric pressure.
Dr. Henry Scott, of Indiana University South Bend, related the
significance of the experiments to conventional hydrocarbon resources:
“Although it is well-established that commercial petroleum originates from
the decay of once-living organisms, these results support the possibility
that the deep Earth may produce abiogenic hydrocarbons of its own.”
“This paper is important,” remarked Dr. Freeman Dyson, professor emeritus
at the Institute for Advanced Study at Princeton who reviewed the study.
“Not because it settles the question whether the origin of natural gas and
petroleum is organic or inorganic, but because it gives us tools to attack
the question experimentally. If the answer turns out to be inorganic,
this has huge implications for the ecology and economy of our planet as
well as for the chemistry of other planets.”
Contacts:
Dr. Russell Hemley
Carnegie Institution Geophysical Laboratory
Phone: 202-478-8951
E-mail hemley@gl.ciw.edu
Dr. Henry Scott
Indiana University South Bend
Phone: 574-520-5527
E-mail: hpscott@iusb.edu
Dr. Ho-kwang (Dave) Mao
Carnegie Institution Geophysical Laboratory
Phone: 202-478-8960
E-mail: mao@gl.ciw.edu
