Geological Survey Organic Origins of Petroleum http://energy.er.usgs.gov/gg/research/ petroleum_origins.html See also: Gasoline and other petroleum fuels; Meth-ane; Oil and natural gas d
Trang 1Speight, James G The Chemistry and Technology of
Petro-leum 4th ed Boca Raton, Fla.: CRC Press/Taylor &
Francis, 2007
_ Handbook of Petroleum Product Analysis
Ho-boken, N.J.: Wiley-Interscience, 2002
Web Sites
OTS Heavy Oil Science Centre
The Chemistry of Petroleum
http://www.lloydminsterheavyoil.com/
petrochem01.htm#Introduction
U.S Geological Survey
Organic Origins of Petroleum
http://energy.er.usgs.gov/gg/research/
petroleum_origins.html
See also: Gasoline and other petroleum fuels;
Meth-ane; Oil and natural gas distribution; Oil and natural
gas drilling and wells; Oil and natural gas exploration;
Oil and natural gas formation; Oil industry; Propane
Oil and natural gas distribution
Category: Energy resources
The majority of the world’s reserves of crude oil and
natural gas are concentrated in a few regions About
two-thirds of the world’s reserves are in Middle East
nations Saudi Arabia has larger oil reserves than any
other country at about 260 billion barrels; Iraq, the
United Arab Emirates, Kuwait, and Iran each have
re-serves of about 100 billion barrels The United States
has less than 2 percent of the world’s reserves.
Background
Petroleum (crude oil and natural gas) is a mixture
of many kinds of hydrocarbon compounds—organic
molecules made largely of hydrogen and carbon
Crude oil is refined to produce a variety of fluid fuels
which, with natural gas, provide most of the energy
that powers the world’s industrialized societies
Petro-leum also provides raw materials for the manufacture
of plastics, synthetic fabrics, many medicines,
fertiliz-ers, insecticides, road pavement, floor coverings,
roof-ing materials, and hundreds of other products
History of Production Large-volume production of petroleum began in the United States, and until 1974, the United States was the world’s leading petroleum producer The United States, however, was endowed with only about 11 per-cent of the world’s original producible oil, so the country was soon ahead of the rest of the world in de-pletion of petroleum resources
In 1974, the Soviet Union replaced the United States as the world’s leading oil-producing country, but oil production declined precipitously in the for-mer Soviet Union from 1988 to 1995 Saudi Arabia then became the leading oil producer As of 2008, the former Soviet Union was second, and the United States was third in oil production
Distribution of Reserves Reserves of a natural resource are the economically producible deposits that have been discovered but not yet consumed About two-thirds of the world’s ap-proximately 1.25 trillion barrels of oil reserves are in the Middle East nations near the Persian Gulf Saudi Arabia has larger oil reserves than any other country
in the world About 260 billion barrels of oil, about 20 percent of the entire world’s oil reserves, are in Saudi Arabia Iraq, the United Arab Emirates, Kuwait, and Iran each have reserves of about 100 billion barrels of oil Most of the remaining global reserves are in Can-ada, Venezuela, the countries of the former Soviet Union, and Mexico, which have 60 billion to 90 bil-lion barrels each, and in Kazakhstan, Libya, Nigeria, the United States, and China, which have 16 billion to
41 billion barrels each The United States, which has produced more oil than any other nation in the world and is the world’s leading oil consumer, has oil re-serves of only about 21 billion barrels, which is less than 2 percent of the global total
The world has about 175 trillion cubic meters of nat-ural gas reserves, about two-thirds of which is in the for-mer Soviet Union and the Middle East The leading producers of natural gas are the former Soviet Union and the United States The United States, in 2008, pro-duced approximately one-fourth of the global natural gas output Nevertheless, the United States’ natural gas consumption rate is great enough that its natural gas production cannot satisfy domestic demand For this reason, the United States imported more than 20 per-cent of the natural gas that it consumed in 2008 U.S reserves of natural gas reached their maxi-mum of 8.2 trillion cubic meters in 1968 and had
Trang 2minished to 4.5 trillion cubic meters by 1995 This
45-percent decline reflects increasing consumption rates
as well as progressively less success in domestic
explo-ration for natural gas Discovery of new reserves and
improved technology boosted the U.S reserves to 6.8
trillion cubic meters in 2009
Future Production and Consumption
Global consumption of natural gas was approximately
3.05 trillion cubic meters in 2007 At this
consump-tion rate, the global reserve of natural gas would
pro-vide about fifty-eight years of supply The average
esti-mate of undiscovered producible natural gas is about
141.6 trillion cubic meters, or an additional sixty-three years of supply Thus, gas reserves plus the mean estimate of undiscovered producible gas sum to more than one hundred years of supply at the 2007 con-sumption rate However, the natural gas concon-sumption rate, like that of oil, does not remain constant Rather,
it has grown historically From 2004 to 2008, annual world consumption of natural gas increased approxi-mately 10 percent A century of supply at the 2009 consumption rate is only fifty-five years of supply if the consumption rate grows 2 percent per year It is only forty-six years of supply if the consumption rate grows
3 percent per year
U.S Energy Information Administration,
Source: International Energy Annual, 2005
4,139 3,609 3,334 2,698 2,627 2,565 2,535 2,529 2,369
Thousands of Barrels per Day
75,000 60,000
45,000 30,000
15,000 Kuwait
Nigeria
Norway
Mexico
China
Iran
Venezuela
United Arab
Emirates
Canada
73,807 9,550
9,043 5,178
United States
Russia
Saudi Arabia
World
Crude Oil: Leading Producers, 2005
Trang 3Moreover, the consumption rate cannot continue
to increase until the resource is depleted Rather, the
unrestricted production rate of a finite natural
re-source reaches its maximum and begins to decline
when about one-half of the total producible resource
has been consumed This is why the U.S oil
produc-tion rate began declining in 1970 in spite of improved
exploration and drilling technology and in spite of
record high rates of exploration for oil during the
early 1980’s The United States is now dependent on
foreign sources for approximately two-thirds of the oil
it consumes
Since the drilling of the first commercial oil well in
1858, the world oil production rate has grown
tremen-dously From 1858 to 1973, global oil consumption
grew at an average rate of about 7 percent per year,
with a consequent doubling of the oil consumption
rate every decade As a result, the world consumed
more oil from 1960 to 1973 than it had consumed
throughout its entire pre-1960 history
Since 1973, this rate of growth has diminished
considerably Nevertheless, the world has consumed
more than twice as much oil since 1973 as
through-out its entire pre-1973 history As is the case for
natu-ral gas, the oil consumption rate cannot continue to
grow indefinitely The 1.25 trillion barrels of global
oil reserves added to the 550 billion barrel average
estimate of producible oil yet to be discovered plus
the more than 1.125 trillion barrels of oil already
consumed total 2.925 trillion barrels of ultimate oil
consumption At the 2008 global oil consumption
rate of 31 billion barrels per year, the world will
have consumed one-half of all the producible oil it
ever had by the year 2018 World oil production rate
will reach its maximum and begin its permanent
de-cline within a decade of that year This is a serious
prospect for governments to contemplate, because
the industrialized world’s history of unprecedented
economic growth during the twentieth century has
been based largely on increasing availability of cheap
petroleum
Oil-producing nations will not all pass their peaks
in oil production rate at the same time The United
States, as stated, passed this point in 1970 and has
since seen its crude oil production drop from a record
high of 9.6 million barrels per day in 1970 to about 8.5
million barrels per day for 2008 The former Soviet
Union also has passed its maximum in oil production
rate As oil production in the rest of the world
de-clines, only the Middle East nations will have the
ex-cess oil production capacity neex-cessary to compensate for increasing production rates However, the Middle East countries as a whole will reach the midpoint of their ultimate oil production well before the year
2020 As they pass their maximum oil production rate, they will not be able to delay the beginning of perma-nent decline in world oil production beyond the sec-ond decade of the twenty-first century The economic and social implications of this coming event demand serious planning by the world’s governments Major discoveries of new oil sources in 2009 in a number of countries proved to be the largest increase
in oil reserves since 2000 New drilling technology has made it possible to extract oil previously thought to be unavailable Reserves were found in the Kurdish re-gion of Iraq, Australia, Israel, Iran, Brazil, Norway, Ghana, and Russia The year 2009 was also a banner year for natural gas, with the discovery of a large field
in Venezuela While cause for optimism, if the price of oil falls, exploration will again decline and total re-serves will again begin a rapid decline
Craig Bond Hatfield
Further Reading
Ahlbrandt, Thomas S., et al Global Resource Estimates from Total Petroleum Systems Tulsa, Okla.: American
Association of Petroleum Geologists, 2005
Aubrecht, Gordon J., II Energy: Physical, Environmen-tal, and Social Impact 3d ed Upper Saddle River,
N.J.: Pearson Prentice Hall, 2006
Campbell, C J The Golden Century of Oil, 1950-2050: The Depletion of a Resource Boston: Kluwer
Aca-demic, 1991
Cordesman, Anthony H., and Khalid R Al-Rodhan
The Global Oil Market: Risks and Uncertainties
Wash-ington, D.C.: Center for Strategic and Interna-tional Studies Press, 2006
Falola, Toyin, and Ann Genova The Politics of the Global Oil Industry: An Introduction Westport, Conn.:
Praeger, 2005
Hirsch, Robert L., Roger Bezdek, and Robert
Wend-ling Peaking of World Oil Production: Impacts, Mitiga-tion, and Risk Management New York: Novinka
Books, 2007
Klare, Michael T Rising Powers, Shrinking Planet: The New Geopolitics of Energy New York: Metropolitan
Books, 2008
Mills, Robin M The Myth of the Oil Crisis: Overcoming the Challenges of Depletion, Geopolitics, and Global Warm-ing Westport, Conn.: Praeger, 2008.
Trang 4Renton, John J Physical Geology Minneapolis/St Paul,
Minn.: West, 1994
Yergin, Daniel The Prize: The Epic Quest for Oil, Money,
and Power New ed New York: The Free Press, 2008.
Web Site
Central Region Energy Resources Team, U.S
Geological Survey
Ranking of the World’s Oil and Gas Provinces by
Known Petroleum Volumes
http://pubs.usgs.gov/of/1997/ofr-97-463/
97463.html#methods
See also: Athabasca oil sands; Energy politics; Oil and
natural gas chemistry; Oil and natural gas drilling and
wells; Oil and natural gas exploration; Oil and natural
gas formation; Oil and natural gas reservoirs; Oil
in-dustry; Organization of Arab Petroleum Exporting
Countries; Organization of Petroleum Exporting
Countries; Peak oil; Russia; Saudi Arabia; United
States; Venezuela
Oil and natural gas drilling and wells
Categories: Energy resources; obtaining and using
resources
Wells drilled to produce oil and natural gas are
de-signed to pump oil as long as the source is economically
viable; they often provide many years of service.
Drilling procedures are rigorous and exacting and are
intended to avoid hazards such as blowouts.
Background
Oil and natural gas are recovered through drilled wells
that are designed and constructed to ensure many
years of service These wells may vary from a few
hun-dred meters to more than 6,000 meters in depth They
must recover oil and gas from their reservoirs in the
subsurface The location of the well is determined by
an exploration team, which produces maps of the
subsurface showing possible accumulation of oil and
gas A team of land agents investigates the ownership of
the drill location and provides information so that the
right to produce the oil and gas can be secured from
the landowner—be it an individual, a state, the federal
government, or a foreign nation After the right to drill
is secured, the drilling plan is converted into action
Drilling Procedures
A suitable drilling rig is selected through the solicita-tion of informasolicita-tion from drilling companies After selection and transportation to the drilling site, the rig is positioned over the marked location, which has been accurately determined by surveying instru-ments A drill bit is connected to drill pipe and drill collars Drill collars are thick-walled cylinders about 9 meters in length used immediately above the drill bit
to prevent the bit from wandering as it cuts through rock formations of varying strength and inclination The drill pipe and collars are rotated by a rotary table
at the surface, causing the drill bit to rotate The weight of the drill string, as the downhole assembly is called, along with its rotation, causes the rock under-neath the bit to be crushed This crushed rock is circu-lated to the surface by drilling fluid This fluid, called
“mud,” is a mix of chemicals suited to the downhole environment It is pumped down the well through the drill string, through the bit nozzles, and then back up
to the surface in the annular space between the drill string and the wall of the drilled hole
The drill bit eventually becomes dull and must be replaced When this happens, the drill string must be unscrewed so that the bit can be brought to the sur-face This process is called “tripping the bit.” The drilled hole must be lined with steel casing to prevent slumping of the borehole wall and unwanted migra-tion and mixing of subsurface fluids Casing is similar
to the steel pipe seen in pipelines on the surface, but it
is designed for the pressures and temperatures en-countered in the subsurface Casing setting depths are either predetermined or selected while drilling to control a hazardous condition such as a blowout or lost circulation
After the first casing “string” is run, it is secured in the borehole by circulating a thin cement slurry down-ward through the casing, then up the annular space between the casing wall and the borehole wall Two casing strings are necessary in the simplest well, while several strings may be necessary for deep wells As ad-ditional casing strings are run, each succeeding string must be smaller in diameter than its predecessor In this way, an oil and gas well becomes smaller in diame-ter as its depth increases For example, it is common
to begin at the surface with a drill bit one-third meter
in diameter, while the final well diameter at total depth may be as small as one-tenth meter This con-cept is simple to understand by noting that as each casing string is secured in the wellbore, the
Trang 5ing bit size must be reduced in order to enter the
newly secured casing
When the borehole penetrates the rock formation
containing oil and gas, the depths of interest are
eval-uated using electrical, acoustic, and radioactive
tech-niques to determine the presence of oil and gas If the
evaluation indicates that oil and gas are there in
com-mercial quantities, “completion” of the well is begun
Completion involves installing the final casing string,
perforating the casing wall adjacent to the rock
for-mation containing oil and gas by using gas jets or
me-chanical cutters, and installing production equipment
Depending on the initial success of the completion
procedure, additional measures may be necessary to
increase the rate of oil and gas produced These
mea-sures include using reactive chemicals to dissolve the rock formation near the wellbore or using hydraulic pressure to fracture the rock formation After the completion procedure, the well is tested to determine the rate of oil and gas being produced Depending on the rate of production, a small string of pipe called tubing is placed inside the casing to provide a flow conduit for the produced fluids
Most oil and gas wells are drilled as near to vertical
as possible The reason is that most regulatory agen-cies closely monitor the surface and bottomhole loca-tions of wells in order to protect mineral property rights In many situations, however, it is impossible to locate the drilling rig over the desired bottomhole lo-cation A river, lake, or building, for example, on the surface may necessitate the drilling of a well direction-ally to the desired bottomhole location The progress
of drilling is monitored by noting the azimuth (devia-tion from true north) and dip (devia(devia-tion from verti-cal) of the well on a continual basis Specialized direc-tional drilling consultants oversee this complicated task Sometimes wells are started vertically at the sur-face, then forced to dip all the way to the horizontal, then kept horizontal in the subsurface Horizontal wells are much more expensive to drill than vertical wells, but good ones yield production rates far in ex-cess of vertical wells
A unique situation for well deviation exists off-shore A series of wells is drilled from an offshore loca-tion The pattern of these wells, called a template, in-cludes the deviation of all but the well immediately underlying the platform or floating rig The proper locating of many wells from the same surface location ensures the broadest distribution of bottomhole loca-tions and involves highly specialized technical knowl-edge
Hazards During the drilling of a well, potential hazards must
be recognized by the drilling personnel These in-clude blowouts and lost circulation A blowout is the uncontrolled escape of subsurface fluids to the sur-face These spectacular events have been identified with the oil and gas industry since its beginnings, and they remain as one of its most newsworthy subjects A properly drilled well should not encounter a blowout
if adequate diagnosis and detection are made The weight of the drilling fluid may be increased to con-trol abnormal pressures in the subsurface Blowout preventers, a type of valving used with the drilling rig,
An engineer guides a directional-drilling motor at a natural gas
drilling facility in Fort Worth, Texas (Getty Images)
Trang 6are designed to protect against blowouts until the well
can be controlled and drilling resumed without
spoil-ing the surface area adjacent to the well
Lost circulation involves drilling fluid that is lost
because it seeps into the pore space or fractures in the
subsurface rock formations If enough drilling fluid
escapes downhole, well control can be lost and a
blow-out can occur Lost circulation is controlled by
de-creasing the weight of the drilling fluid or using
plug-ging agents circulated into the subsurface leak zones
Oil and Gas Pumping and Production
When the well has been completed and production is
assured, a wellhead is installed to replace the blowout
preventers The wellhead, nicknamed the “Christmas
tree,” is a series of valves designed to seal the casing, its
annular space, and the tubing to prevent leaks
Crude oil is processed at the site only to remove
un-wanted foreign matter Surface equipment used to
process oil and gas includes dehydrators to remove
water and water vapor, and separators to remove
for-eign matter, including rock particles, paraffin, and
other debris prohibited by the buyer of the oil and
gas Large tanks are used to store oil prior to delivery
Oil is transported by pipeline, truck, and train to
the refinery for further breakdown into gasolines,
motor oils, and other products and chemicals
Natu-ral gas is odorized by placing a distinctive odorant in
it, and its pressure is elevated by compression for
de-livery to the customer through a series of pipelines
An ideal oil and gas well will flow to the surface
us-ing its internal energy Oil wells eventually reach the
point where their flowing energy is depleted and they
must be pumped in order to continue producing A
variety of pumps have been used in the oil and gas
in-dustry; among them is the familiar beam pump,
some-times called a “horse’s head” or “nodding donkey,”
that is seen in oil-producing areas around the world
Depletion and Economic Limit
When a well’s energy is depleted, an enhanced oil
recovery (EOR) project may be started EOR
tech-niques are used to produce additional oil from an oil
and gas formation that has depleted its primary
en-ergy source Various fluids ranging from fresh water to
exotic liquids, gases, and even steam are injected into
oil-producing rocks to force more oil from them
Of-ten EOR projects can produce an amount of oil
equiv-alent to that recovered during the well’s primary
op-erating life
All oil and gas wells eventually reach their “eco-nomic limit,” at which point eco“eco-nomic production ceases The economic limit is an arbitrary production rate that depends on the expenses associated with producing the well, the percentage of ownership of the well’s operator, and the price of the oil and gas This limit may be reached in a short period after pro-duction begins for poorly performing wells, or it may exceed fifty years Once the production rate falls below the economic limit, the well is either plugged and abandoned (cement plugs are used to seal the wellbore) or converted into a liquid disposal or EOR injection well After the well’s operators have plugged the wellbore to the satisfaction of regulatory authori-ties, the surface location in the vicinity of the well is restored in an environmentally acceptable manner Little or no trace of the well itself should be left
Charles D Haynes
Further Reading
Beggs, H Dale Gas Production Operations Tulsa, Okla.:
OGCI, 1984
Boomer, Paul M A Primer of Oilwell Drilling 7th ed.
Austin, Tex.: Petroleum Extension Service, Univer-sity of Texas, 2008
Devereux, Steve Drilling Technology in Nontechnical Language Tulsa, Okla.: PennWell, 1999.
Economides, Michael J., A Daniel Hill, and Christine
Ehlig-Economides Petroleum Production Systems
En-glewood Cliffs, N.J.: PTR Prentice Hall, 1994
Hyne, Norman J Nontechnical Guide to Petroleum Geol-ogy, Exploration, Drilling, and Production 2d ed Tulsa,
Okla.: PennWell, 2001
Miesner, Thomas O., and William L Leffler Oil and Gas Pipelines in Nontechnical Language Tulsa, Okla.:
PennWell, 2006
Moore, Preston L Drilling Practices Manual 2d ed.
Tulsa, Okla.: PennWell, 1986
Nind, T E W Principles of Oil Well Production 2d ed.
New York: McGraw-Hill, 1981
Web Site How Stuff Works How Oil Drilling Works http://science.howstuffworks.com/oil-drilling5.htm See also: Gasoline and other petroleum fuels; Oil and natural gas distribution; Oil and natural gas ex-ploration; Oil industry; Propane
Trang 7Oil and natural gas exploration
Categories: Energy resources; obtaining and using
resources
Drilling for oil is the last step in oil exploration Surface
mapping, the use of seismic technology to study
sedimen-tary rock sequences, and other geological and
geophysi-cal studies all precede drilling Oil and gas exploration
is also driven by market forces that lead companies to be
more or less likely to look for new sources of petroleum
depending on the price of oil and natural gas.
Background
Petroleum (crude oil and natural gas) is a mixture of
hydrocarbons, which are organic compounds made
largely of hydrogen and carbon Exploration for
pe-troleum accelerated during the early 1900’s as
de-mand for fluid fuels increased following the
develop-ment of the internal combustion engine By the early
twenty-first century, oil companies were looking for
traditional sources of oil and gas as well as new sources,
such as oil shale and oil sands Throughout the
his-tory of oil and gas exploration, the price of oil and gas
has influenced oil companies’ decisions to explore
for new resources Technology has also influenced
exploration both from the technical ability of
compa-nies to find new sources and the drilling capabilities
of oil companies As demand for oil and natural gas
has increased, companies have explored new, often
more challenging areas for supplies
Origin of Petroleum
Oil and natural gas are formed over immense spans of
time from microscopic floating marine organisms
that live by the billions in the world’s oceans As these
die and sink to the seafloor, they may be buried in
ar-eas where there is rapid influx of sediment from
ero-sion of adjacent land When buried by mud, and thus
removed from contact with oxygen dissolved in
seawa-ter, the organic matter cannot completely decompose
to gases, as it otherwise would
If sediment continues to accumulate, the high
con-fining pressure and high temperature at depth can
change the organic matter to liquid or gaseous
hydro-carbons—crude oil or natural gas As compaction
changes the sediment to rock, the fluid hydrocarbons
are squeezed out of the sediment originally
contain-ing them and move upward through the compactcontain-ing
sedimentary accumulation The petroleum may mi-grate upward into a coarser sediment, such as sand Sand can be very permeable to fluid migration cause of the large interconnected pore spaces be-tween adjacent sand grains The petroleum continues
to rise through such a sand layer because most of the pore space in marine sediments and sedimentary rocks is filled with water, and petroleum is less dense than water During this upward migration, if the pe-troleum encounters a fine-grained sedimentary layer that will not permit fluids to move through it, then the petroleum can be restricted to a particular porous zone, such as a sandstone layer beneath the fine-grained barrier
In some regions, the petroleum-bearing sedimen-tary rocks may be folded or otherwise deformed so that they are no longer a sequence of horizontal lay-ers In this way, the petroleum can be concentrated in commercial quantities Commonly, petroleum is con-centrated in the highest parts of the deformed or folded layer containing it, because all the pore space beneath is filled with seawater Thus, exploration for oil and natural gas requires study of sedimentary rock sequences that extend hundreds of meters or even several kilometers into the subsurface The settings in which these sequences accumulated and the geo-graphic distributions and thickness variations of the sedimentary layers must be understood
Some liquid petroleum is compressed into what are known as oil sands Oil sands were probably formed when conventional oil was trapped in shallow reser-voirs Over time, the water and lighter hydrocarbons were washed away or consumed by bacteria, leaving dense compounds that are often contaminated by high levels of sulfur and some heavy metals Because oil can be extracted from oil sands, these formations have become a potential source of oil
Searching for Petroleum Most sedimentary rocks were not deposited in set-tings in which large quantities of organic matter were preserved Even if the sedimentary rocks are rich in petroleum-forming hydrocarbons, subsequent defor-mation of the rocks most commonly has not produced
a potential trap to concentrate the petroleum in com-mercial quantities Deep drilling is very expensive, and most wells do not find commercial concentra-tions of petroleum In order to know where to locate exploratory wells, various kinds of geological studies must precede drilling
Trang 8The search for petroleum includes the study of
sed-imentary rocks at depth using geophysical techniques
such as seismic studies Seismic studies generate,
com-monly via explosions, sound waves that are reflected
and refracted (bent) by the sedimentary layers in the
subsurface The sound returning to the surface is
re-corded by sensitive receivers, and reflections from
lay-ers of particular rock types can be recognized The
time required for the sound to travel to a particular
sedimentary rock layer and be reflected from it back
to the surface is used to determine the depth of the
sedimentary layer The velocity of sound through a
given layer is a function of the rock density, which in
turn is an indication of rock type After surface
map-ping, seismic examination of the subsurface, and
other geological and geophysical studies have
re-vealed sufficient information, it is possible to place
ex-ploratory wells in locations where there is higher
probability of petroleum discovery
Initially, most oil exploration was done in the United States, especially in Texas, Louisiana, Califor-nia, and Oklahoma By the early twentieth century, geologists were finding large oil deposits in the Cas-pian Sea region and Mexico The discovery of large oil deposits occurred subsequently in the Middle East, especially in Saudi Arabia In the early twenty-first century, geologists continued to find oil and natural gas fields in these areas, but also in Indonesia, Libya, Nigeria, Sudan, China, Kazakhstan, and Russia Off-shore oil and gas deposits were first located in shallow water in the Gulf of Mexico in the early twentieth cen-tury Offshore oil continues to be found in shallow water but also in water depths of more than 3,000 me-ters in the Gulf of Mexico as well as in the North Sea off the coast of Norway, off the Brazilian coast, along the east coast of Africa, and in Southeast Asia, near In-donesia Greatly improved technology has made pos-sible both the discovery of these fields and the ability
to drill for oil and gas The last two major un-explored regions of the world in terms of oil and natural gas deposits are the Arctic Ocean and Antarctica
Petroleum Supply Problems
In spite of improving technology, the search for petroleum became less successful by the 1990’s However, late in that decade, tion efforts increased Petroleum explora-tion and large-scale petroleum producexplora-tion began in the United States earlier than in any other country, and for many decades prior to
1974, the United States was the world’s lead-ing oil producer Partly for these reasons, U.S petroleum resources are being depleted earlier than those of the rest of the world The oil fields closest to the Earth’s surface were the easiest to find and therefore were the first to be discovered As exploration and exploitation of petroleum resources contin-ued and grew, oil fields became increasingly difficult to find In the United States, where exploration for petroleum began, oil compa-nies have nearly run out of places to look for large, new oil fields Even for the world as a whole, petroleum has become progressively more difficult or, at least, more expensive to find, so that the search for it has extended into hostile climatic environments and unsta-ble political situations In some cases, oil
A Texas oil well spouts “black gold” in the 1920’s (Library of Congress)
Trang 9panies are also reevaluating old oil fields because new
technologies allow extraction of oil that was
previ-ously unobtainable
In the history of any oil-producing region, the oil
discovery rate reaches its maximum several years
be-fore the maximum in oil production rate For
exam-ple, in the United States (exclusive of Alaska), the oil
discovery rate reached its peak in the late 1950’s and
diminished greatly afterward However, the U.S oil
production rate reached its maximum in 1970 and
de-clined afterward The global oil discovery rate was at
its maximum in the 1960’s and diminished afterward
in spite of record-high rates of exploration in the early
1980’s The global oil-production rate, however, as
the end of the twentieth century, had not yet reached
its maximum Some geologists indicate that the world
oil peak could occur early in the twenty-first century
Other scholars, particularly economists, indicate that
as prices rise there will be an increased incentive to
discover more oil and natural gas There continues to
be extensive debate concerning when oil and gas
pro-duction will peak
Global Oil Reserves
The reserves of a natural resource are that amount
which has been discovered but not yet consumed
There is an ongoing debate about how to estimate
re-serves, and some countries and oil companies either
over- or underestimate reserves for their own ends By
the late twentieth century, consumption rates were
such that global reserves of conventional oil were
ex-pected to last for forty years The consumption rate,
however, does not remain constant; rather, it has
grown historically In 1996, the world oil consumption
rate was growing more than 2 percent annually A
forty-year supply at the 1996 consumption rate
be-comes a thirty-year supply with a 2 percent growth in
consumption per year After some debate and the
dis-covery of new oil deposits, published oil reserves in
2007 were more than 1.2 trillion barrels for
conven-tional oil, extending the consumption time horizon
Although additional reserves were discovered in the
early twenty-first century, consumption rates have
in-creased, due in part to the rapid industrialization
oc-curring in countries such as China and India Global
natural gas reserves plus estimates of undiscovered
producible gas resources are a few decades larger
than those for oil as measured in terms of remaining
consumption time
Discovery of oil from 1985 to 1995 averaged less
than 9 billion barrels annually, while consumption rates averaged more than 23 billion barrels annually
In other words, most of the oil burned during this in-terval had been discovered during earlier decades By the early twenty-first century, the discovery rate had increased to about 11 billion barrels per year Using these data, Saudi Arabia has the world’s largest oil re-serves, followed by Iran These reserve figures are based on conventional oil and gas supplies If uncon-ventional sources, such as oil sands, are taken into ac-count, Canada’s potential oil reserves rival those of Saudi Arabia If global oil consumption continues to grow at the 2 percent rate, and if oil discovery rates continue to decline, global reserves of oil will dwin-dle Scientists agree that oil and natural gas are in lim-ited supply, but increased exploration and drilling and recovery technologies implemented in the early twenty-first century are pushing back the date at which demand for oil and gas will exceed supply Some com-mentators indicate that market forces are once again driving oil companies to explore all opportunities for oil and gas extraction
Exploration for and Production of New Sources
As world demand for oil and natural gas has in-creased, oil companies have turned to alternative ar-eas and techniques in the search for petroleum re-sources High prices for oil and natural gas have made feasible drilling for oil in increasingly harsh environ-ments or turning to unconventional oil such as oil sands
In addition to seeking out new sources for liquid petroleum, oil companies have also turned to two other strategies One is to return to old oil fields and explore them in order to evaluate how much oil re-mains in the ground Earlier drilling did not extract all of the oil in a reservoir; often nearly one-half of the reservoir remained New technologies such as saltwa-ter infusion and side drilling make exploiting old oil fields possible Another approach that some of the oil companies have used is to mine oil sands, especially in Alberta, Canada Once the overburden has been stripped away from the oil sands, these oil sands are heated and compressed so as to extract the oil Be-cause this process is expensive and requires a good deal of energy to remove the oil from the other mate-rial, oil companies have only recently begun to en-gage in full-scale exploration for oil sands as the price
of conventional oil increased to more than one
Trang 10dred dollars per barrel Exploration of potential oil
sands is ongoing in several areas of the world in
addi-tion to Canada, including Venezuela
Oil companies are also exploring regions that have
traditionally been ignored, such as East Africa Most
of the exploration for new sources of oil and natural
gas has been concentrated on the ocean floor,
espe-cially off the west coast of Africa, off the coast of Brazil,
and in areas bordering Indonesia Some scientists also
contend that oil and natural gas is available in the
South China Sea, but the disputes between the
bor-dering countries have made exploration unfeasible
Another area under consideration is the seabed of
the Arctic Ocean Drilling technology exists to drill
through 3,660 meters of water and another 3,000
me-ters of rock Thus, companies are now engaged in
looking for oil and natural gas in deepwater sites that
would have been impossible to exploit a few years ago
Oil and gas exploration continue to be driven by
what seems to be an insatiable world demand for
pe-troleum for energy and other uses, such as for the
chemical industry Improvements in technology have
increased the ability of geologists and geophysicists to
explore for oil and gas in new places Improved
tech-nology also means that wells can be drilled in places
that were impossible a few years ago Therefore,
com-panies are willing to explore for oil in challenging
places
Craig Bond Hatfield, updated by John M Theilmann
Further Reading
Blanchard, Roger D The Future of Global Oil Production:
Facts, Figures, Trends and Projections, by Region
Jeffer-son, N.C.: McFarland, 2005
Deffeyes, Kenneth Hubbert’s Peak: The Impending
World Oil Shortage Rev ed Princeton, N.J.:
Prince-ton University Press, 2003
Downey, Marlan W., Jack C Threet, and William A
Morgan, eds Petroleum Provinces of the Twenty-first
Century Tulsa, Okla.: American Association of
Pe-troleum Geologists, 2001
Funk, McKenzie “Arctic Landgrab: As the Ice
Shrinks, Nations Vie for Oil That May Lie
Be-neath.” National Geographic 215, no 5 (2009): 104.
Howard, Roger The Oil Hunters: Exploration and
Espio-nage in the Middle East, 1880-1939 New York:
Hambledon Continuum, 2008
Hunt, John M Petroleum Geochemistry and Geology 2d
ed New York: W H Freeman, 1996
Hyne, Norman J Nontechnical Guide to Petroleum
Geol-ogy, Exploration, Drilling, and Production 2d ed.
Tulsa, Okla.: PennWell, 2001
Kunzig, Robert “The Canadian Oil Boom: Tar Sands
Yield Millions of Barrels—But at What Cost?” Na-tional Geographic 215, no 3 (2009): 34.
Leffler, William L., Richard Pattarozzi, and Gordon
Sterling Deepwater Petroleum Exploration and Produc-tion: A Nontechnical Guide Tulsa, Okla.: PennWell,
2003
Mills, Robin M The Myth of the Oil Crisis: Overcoming the Challenges of Depletion, Geopolitics, and Global Warm-ing Westport, Conn.: Praeger, 2008.
Stoneley, Robert Introduction to Petroleum Exploration for Non-Geologists New York: Oxford University
Press, 1995
See also: Athabasca oil sands; Integrated Ocean Drilling Program; Landsat satellites and satellite tech-nologies; Oil and natural gas chemistry; Oil and natu-ral gas distribution; Oil and natunatu-ral gas drilling and wells; Oil and natural gas formation; Oil industry; sources as a medium of economic exchange; Re-sources as a source of international conflict; Seismo-graphic technology and resource exploitation
Oil and natural gas formation
Categories: Energy resources; geological processes and formations
The formation of usable oil and gas deposits involves the deposition, transformation, and migration of vari-ous types of organic material; these processes take place over huge expanses of time.
Background Oil, or petroleum, is not a single chemical compound but a variety of liquid hydrocarbon compounds—that
is, compounds made up of different proportions of the elements carbon and hydrogen There are also gaseous hydrocarbons—natural gas—of which the compound methane (CH4) is the most common The relative amount of oil and gas produced from any source rock depends principally on the ratio of hydro-gen to carbon The formation of any fossil fuel re-quires a large initial accumulation of biomass rich in carbon and hydrogen Another requirement is that the organic debris be buried quickly to protect it from