Location, Location, Location: Mapping the World’s Oil & Gas Giants
August 2007
Want to find the next giant oil or gas field? Then look at
the map produced by Paul Mann and his colleagues.
Mann—senior research scientist at the Institute for Geophysics at
The University of Texas at Austin—says it provides some important
clues. The map of the world’s giants prepared
in collaboration with consultant Mike Horn of
Tulsa, and Ian Cross, a vice-president for IHS,
an energy information company headquartered
in Houston, indicates the location and
tectonic setting of all known giant fields, those
with over 500 million barrels of ultimately
recoverable oil or an equivalent amount of gas.
Spend a little time with the map and you
see that giants understand the old real estate
adage: location, location, location. They prefer
to hang out in about 25 upscale neighborhoods
or clusters. These clusters are very
unevenly distributed around the planet. The
combined cluster areas cover less than a third
of the Earth’s surface.
The Persian Gulf is the largest cluster with
over 200 of the 932 giants the group has identified
so far. The Persian Gulf is a long lived passive
margin of the former Tethyan ocean that
collided with Eurasia in the Cenozoic. Its long
lived history means the rock layering has superimposed
or “stacked” intervals of both high
quality source and reservoir rocks. If the oil
misses one reservoir on its migration upward
there is an overlying reservoir to sop it up. Evaporites
provide seals or “caulking” that prevent
the hydrocarbons from escaping to the surface.
The second densest cluster of giants are the
93 giants of the Western Siberian basin, a huge,
largely on-land rifted area formed during the
Permo-Triassic as Asia tried to split apart.
In fact, as this article was being prepared, an obscure Russian independent
operator announced the discovery of a giant gas field in eastern
Siberia's Irkutsk region. Proceeds from hydrocarbons produced in the
Western Siberian basin are helping to power the revived Russian
economy and make it one of the key oil and gas exporters to eastern
and western Europe.
“We also like to compile on the global map
the top five biggest oil and gas discoveries of
each year and each decade,” says Mann. “That
helps people see at a glance where the hot areas
are, how they change year by year, and what
their tectonic settings are.”
And the winner is…
“One of our main conclusions was that the best
tectonic setting for giants was passive margins
along continents like West Africa or Brazil.”
A close runner-up would be continental rifts
and overlying sag or “steer’s head” basins.
The more restricted the rift during its early
lacustrine or submarine history the better for
forming large areas of high quality, black, smelly,
organic-rich source rocks needed to create large
volumes of oil and gas. For example, failed rifts
that crack the edge of a continent but don’t succeed
in full ocean opening are prime real estate
for concentrating the high quality source rocks
needed for a giant cluster. Examples are the
North Sea, the Western Siberian basin and Bass
Strait separating Tasmania and Australia.
One of the worst places to find giants is a
strike slip margin where complex and ongoing
structural history can disrupt reservoirs. Another
poor setting for giants are subduction zones
where reservoir sandstones are choked with clay
minerals and therefore have limited reservoir
potential for holding large oil and gas deposits.
“You can count giants in subduction settings on one hand,”
says Mann.
“If you’re looking for a giant,” says Mann, “go to those tectonic
environments that are associated with the densest clusters of known
giants. Avoid tectonic environments with poor track records. It’s a
major level of risk that can be avoided at the outset of the search.”
Mann’s analysis shows that collisional settings are less important
in forming giant fields than researchers previously thought.
Behind the Map
Assigning tectonic settings to all 932 known giants is challenging since
individual basins typically undergo many different tectonic phases
often separated by tens to hundreds of millions of years. However,
subsurface data are improving and scientists now have a much better
idea of what these phases were and what their relative importance was
on hydrocarbons.
Most basins have an unequivocal “main event” that shapes their
structure, stratigraphy and their associated giant fields. Mann also
uses software developed by Larry Lawver and Lisa Gahagan of the
Institute for Geophysics’ PLATES project to show how moving plates
have affected the history and location of giants (see PLATES sidebar).
The team’s work follows closely the earlier efforts of legendary oil
finder Michel Halbouty, who tracked trends in giant discoveries from
the 1960s to his death at age 95 in 2004. In Halbouty’s fourth and last
edited volume on the topic, “Giant Oil and Gas Fields of the Decade,
1990-1999,” Mann and his colleagues were invited to contribute a
paper on their work on the tectonic setting of giant fields.
“Once we pulled the database together for this paper, it has
become less of a chore to update it each year,” he says. Fifty seven giant
oil and gas fields were discovered in the period from 2000 to 2005.
Computer technology makes it easier to track the locations and
main characteristics of the many giants.
“We can click on any giant field on our map and pull up a
spreadsheet of its main characteristics,” says Mann. “We plot the basin
locations on geologic maps to gain understanding of their tectonic
settings. We mine the published literature for seismic and well data
to construct a database for each giant field. We can sort fields which
share particular characteristics including production figures or
geologic characteristics like reservoir types.”
The value of such a compilation is to show how common patterns
start to emerge in basins that share common tectonic environments:
even though those environments are separated by thousands of kilometers
or tens of millions of years. What appears initially as a hopelessly
tangled geologic history starts to become simpler and more
understandable once you fully mine the regional geologic databases
and reconstruct the basin at the time of the giants’ formation.
There appears to be a lot of interest among energy industry
experts in the map. “The AAPG Memoir in which this first appeared
[in 2003] has sold out,” says Horn. “You can’t get it anymore. That’s
rare for an AAPG Memoir to run out of press—and that was just
three years ago.”
Running on Empty?
Discoveries of giants, which make up roughly half the world’s oil and
gas reserves, have declined since the 1970s. No one argues about that,
says Mann. The decline has led some experts to predict that oil and
gas will run out in the next few decades.
Mann says his team’s mapping and tabulation of fields helps
to show how these trends are evolving decade by decade and how
improving technologies like 3D seismic data are impacting the hunt.
“There are 932 giants on our giants map at the moment,” he says.
“Working with Ian Cross, our collaborator at the Global Petroleum
Information department of IHS, we are always adding new ones and
classifying their tectonic settings. We greatly appreciate Ian’s collaboration
since he keeps us up to date with the latest discovery information
from the industry.”
In return, says Cross, the collaboration has increased the credibility
of IHS within the energy industry: “Because of Paul’s good reputation
in the industry, his use of the data elevates our image.” Cross also
says that Mann helped them refine their data.
Both agree it has been a fruitful academic-industry partnership.
“At such a global scale,” says Mann, “we can identify regional
trends that may not be obvious to petroleum geologists working at
much more local scales within well known giant cluster areas like the
Gulf of Mexico, Persian Gulf or Western Siberian basin.”
Of particular interest in their compilation are the new giants
that are discovered in areas with no previous track record of giants.
These are the potential cluster areas of the future since favorably large
source and reservoir potential exists. Some examples of these new
emerging clusters are the deepwater area of the Bay of Bengal (both
eastern India and Myanmar), the Ordos and Tarim basins of western
China, the Mekong delta of Viet Nam, the Sudan rift of Africa, and
the deepwater area of northern Australia. In all of these areas, geoscientists
are working feverishly to define the size and limits of the
cluster. The larger the cluster area, the better the outlook.
The first part of this decade has seen an uptick in the number of
giant discoveries, despite the overall decline in discoveries since the
1970s. This is a reflection of the tremendous increase in deepwater
exploration of the passive margin and rift environments along
continental margins.
This kind of exploration is extremely expensive.
“To pay for it,” says Mann, “these companies really have to find
giants to make it worthwhile. They have to make big discoveries. If
they find a small field, they can’t develop it because it isn’t economical
to create the infrastructure needed to move the oil or gas from the
offshore area to a refinery.”
This decade is poised to become the third most prolific in history
for the discovery of giants. And that has Horn feeling optimistic
about the future of oil and gas. “I see a turn around,” says Horn.
“There was a burst of activity in the 1960s and 70s with the advent
of digital seismic. We had a major new tool. That was followed by a
rapid decline in the 1980s and 90s. Now we’re seeing a turn around.”
Based on trends in the numbers of annual discoveries, Mann and
colleagues predict that 33 more oil and gas giants will be discovered
before the end of this decade, as reported in their talk at the April
2007 AAPG annual meeting in Long Beach, California.
These big picture, “trendology” type talks are important for
the oil industry since it helps them decide which new areas to look
at and where new data needs to be collected. In short: location,
location, location!
by Marc Airhart and Paul Mann
For more information about the Jackson School contact J.B. Bird at jbird@jsg.utexas.edu,
512-232-9623.
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