Oil reserves
Overview
Oil reservoir
A petroleum reservoir, or oil and gas reservoir, is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. The naturally occurring hydrocarbons, such as crude oil or natural gas, are trapped by overlying rock formations with lower permeability...
, including both producible and non-producible oil, is called oil in place
Oil In Place
Oil in place is the total hydrocarbon content of an oil reservoir and is often abbreviated STOOIP, which stands for Stock Tank Original Oil In Place, or STOIIP for Stock Tank Oil Initially In Place, referring to the oil in place before the commencement of production...
. However, because of reservoir characteristics
Reservoir engineering
Reservoir engineering is a branch of petroleum engineering that applies scientific principles to the drainage problems arising during the development and production of oil and gas reservoirs so as to obtain a high economic recovery....
and limitations in petroleum extraction technologies
Extraction of petroleum
The extraction of petroleum is the process by which usable petroleum is extracted and removed from the earth.-Locating the oil field:Geologists use seismic surveys to search for geological structures that may form oil reservoirs...
, only a fraction of this oil can be brought to the surface, and it is only this producible fraction that is considered to be reserves. The ratio of producible oil reserves to total oil in place for a given field is often referred to as the recovery factor.
Unanswered Questions
Discussions
Encyclopedia
The total estimated amount of oil in an oil reservoir
, including both producible and non-producible oil, is called oil in place
. However, because of reservoir characteristics
and limitations in petroleum extraction technologies
, only a fraction of this oil can be brought to the surface, and it is only this producible fraction that is considered to be reserves. The ratio of producible oil reserves to total oil in place for a given field is often referred to as the recovery factor. Recovery factors vary greatly among oil fields. The recovery factor of any particular field may change over time based on operating history and in response to changes in technology
and economics
. The recovery factor may also rise over time if additional investment is made in enhanced oil recovery
techniques such as gas injection, surfactants injection, water-flooding, or microbial enhanced oil recovery
.
Based on data from OPEC
at the beginning of 2011 the highest proved oil reserves including non-conventional oil deposits are in Venezuela
(20 per cent of global reserves), Saudi Arabia
(18 %,of global reserves), Iran
(9 %).
Because the geology
of the subsurface cannot be examined directly, indirect techniques
must be used to estimate the size and recoverability of the resource. While new technologies
have increased the accuracy of these techniques, significant uncertainties still remain. In general, most early estimates of the reserves of an oil field are conservative and tend to grow with time. This phenomenon is called reserves growth.
Many oil-producing nations do not reveal their reservoir engineering field data and instead provide unaudited claims for their oil reserves. The numbers disclosed by some national governments are suspected of being manipulated for political reasons.
All reserve estimates involve uncertainty, depending on the amount of reliable geologic and engineering data available and the interpretation of those data. The relative degree of uncertainty can be expressed by dividing reserves into two principal classifications—"proven" (or "proved") and "unproven" (or "unproved"). Unproven reserves can further be divided into two subcategories—"probable" and "possible"—to indicate the relative degree of uncertainty about their existence. The most commonly accepted definitions of these are based on those approved by the Society of Petroleum Engineers
(SPE) and the World Petroleum Council (WPC) in 1997.
Proven reserves are further subdivided into "proven developed" (PD) and "proven undeveloped" (PUD). PD reserves are reserves that can be produced with existing wells and perforations, or from additional reservoirs where minimal additional investment (operating expense) is required. PUD reserves require additional capital investment (e.g., drilling new wells) to bring the oil to the surface.
Until December 2009 "1P" proven reserves
were the only type the U.S. Securities and Exchange Commission allowed oil companies to report to investors. Companies listed on U.S. stock exchanges must substantiate their claims, but many governments and national oil companies do not disclose verifying data to support their claims. Since January 2010 the SEC now allows companies to also provide additional optional information declaring "2P" (both proven and probable) and "3P" (proven + probable + possible) provided the evaluation is verified by qualified third party consultants, though many companies choose to use 2P and 3P estimates only for internal purposes.
Unproven reserves are based on geological and/or engineering data similar to that used in estimates of proven reserves, but technical, contractual, or regulatory uncertainties preclude such reserves being classified as proven. Unproven reserves may be used internally by oil companies and government agencies for future planning purposes but are not routinely compiled. They are sub-classified as probable and possible.
Probable reserves are attributed to known accumulations and claim a 50% confidence level of recovery. Industry specialists refer to them as "P50" (i.e., having a 50% certainty of being produced). These reserves are also referred to in the industry as "2P" (proven plus probable).
Possible reserves are attributed to known accumulations that have a less likely chance of being recovered than probable reserves. This term is often used for reserves which are claimed to have at least a 10% certainty of being produced ("P10"). Reasons for classifying reserves as possible include varying interpretations of geology, reserves not producible at commercial rates, uncertainty due to reserve infill (seepage from adjacent areas) and projected reserves based on future recovery methods. They are referred to in the industry as "3P" (proven plus probable plus possible).
Fraud and incompetence
In the early 1980s the Penn Square Bank
of Oklahoma engaged in wide scale lending to Oil and Gas groups with reserves used as collateral
for the loans. Sometimes the bank officers ignored the engineering advice about reserve size and value in order to book the loan profit. The bank resold many of the loans as 'loan participations' to larger banks like Continental Illinois, Seattle First, Michigan National
, and Chase Manhattan
, whose officers also sometimes ignored engineering advice. When the oil market busted, many of these loans were called, and the true nature of the reserves used as loan collateral was discovered by Federal Deposit Insurance Corporation
government investigators and creditors. Penn Square went bust, and Continental Illinois was the first Too Big to Fail
bailout of the modern era.
, approximately 4.1 Goilbbl of oil are held in strategic reserves, of which 1.4 billion is government-controlled. These reserves are generally not counted when computing a nation's oil reserves.
A more sophisticated system of evaluating petroleum accumulations was adopted in 2007 by the Society of Petroleum Engineers (SPE), World Petroleum Council (WPC), American Association of Petroleum Geologists
(AAPG), and Society of Petroleum Evaluation Engineers (SPEE). It incorporates the 1997 definitions for reserves, but adds categories for contingent resources and prospective resources.
Contingent resources are those quantities of petroleum estimated, as of a given date, to be potentially recoverable from known accumulations, but the applied project(s) are not yet considered mature enough for commercial development due to one or more contingencies. Contingent resources may include, for example, projects for which there are currently no viable markets, or where commercial recovery is dependent on technology under development, or where evaluation of the accumulation is insufficient to clearly assess commerciality.
Prospective resources are those quantities of petroleum estimated, as of a given date, to be potentially recoverable from undiscovered accumulations by application of future development projects. Prospective resources have both an associated chance of discovery and a chance of development.
The United States Geological Survey
uses the terms technically and economically recoverable resources when making its petroleum resource assessments. Technically recoverable resources represent that proportion of assessed in-place petroleum that may be recoverable using current recovery technology, without regard to cost. Economically recoverable resources are technically recoverable petroleum for which the costs of discovery, development, production, and transport, including a return to capital, can be recovered at a given market price.
"Unconventional resources" exist in petroleum accumulations that are pervasive throughout a large area. Examples include extra heavy oil
, natural bitumen, and oil shale
deposits. Unlike "conventional resources", in which the petroleum is recovered through wellbores and typically requires minimal processing prior to sale, unconventional resources require specialized extraction technology to produce. For example, steam and/or solvents are used to mobilize bitumen for in-situ recovery. Moreover, the extracted petroleum may require significant processing prior to sale (e.g., bitumen upgraders). The total amount of unconventional oil resources in the world considerably exceeds the amount of conventional oil reserves, but are much more difficult and expensive to develop.
The amount of oil in a subsurface reservoir is called oil in place
(OIP). Only a fraction of this oil can be recovered from a reservoir. This fraction is called the recovery factor. The portion that can be recovered is considered to be a reserve. The portion that is not recoverable is not included unless and until methods are implemented to produce it.
There are a number of different methods of calculating oil reserves. These methods can be grouped into three general categories: "volumetric", "material balance", and "production performance". Each method has its advantages and drawbacks.
Since a system of country production quotas was introduced in the 1980s, partly based on reserves levels, there have been dramatic increases in reported reserves among OPEC producers. In 1983, Kuwait increased its proven reserves from 67 Goilbbl to 92 Goilbbl. In 1985–86, the UAE almost tripled its reserves from 33 Goilbbl to 97 Goilbbl. Saudi Arabia raised its reported reserve number in 1988 by 50%. In 2001–02, Iran raised its proven reserves by some 30% to 130 Goilbbl, which advanced it to second place in reserves and ahead of Iraq. Iran denied accusations of a political motive behind the readjustment, attributing the increase instead to a combination of new discoveries and improved recovery. No details were offered of how any of the upgrades were arrived at.
The following table illustrates these rises.
The sudden revisions in OPEC reserves, totaling nearly 300 bn barrels, have been much debated. Some of it is defended partly by the shift in ownership of reserves away from international oil companies, some of whom were obliged to report reserves under conservative US Securities and Exchange Commission rules. The most prominent explanation of the revisions is prompted by a change in OPEC rules which set production quotas (partly) on reserves. In any event, the revisions in official data had little to do with the actual discovery of new reserves.
Total reserves in many OPEC countries hardly changed in the 1990s. Official reserves in Kuwait, for example, were unchanged at 96.5 Goilbbl (including its share of the Neutral Zone) from 1991 to 2002, even though the country produced more than 8 Goilbbl and did not make any important new discoveries during that period. The case of Saudi Arabia is also striking, with proven reserves estimated at between 260 and 264 Goilbbl in the past 18 years, a variation of less than 2%, while extracting approximately 60 Goilbbl during this period.
Sadad al-Huseini, former head of exploration and production at Saudi Aramco, estimates 300 Goilbbl of the world's 1200 Goilbbl of proven reserves should be recategorized as speculative resources, though he did not specify which countries had inflated their reserves. Dr. Ali Samsam Bakhtiari, a former senior expert of the National Iranian Oil Company
, has estimated that Iran, Iraq, Kuwait, Saudi Arabia and the United Arab Emirates have overstated reserves by a combined 320–390bn barrels and has said, "As for Iran, the usually accepted official 132 Goilbbl is almost one hundred billion over any realistic assay." Petroleum Intelligence Weekly reported that official confidential Kuwaiti documents estimate reserves of Kuwait were only 48 Goilbbl, of which half were proven and half were possible. The combined value of proven and possible is half of the official public estimate of proven reserves.
In July 2011, OPEC's Annual Statistical Review showed Venezuela's reserves to be larger than Saudi Arabia's.
A 2008 United States Geological Survey estimates that areas north of the Arctic Circle have 90 Goilbbl of undiscovered, technically recoverable oil and 44 Goilbbl of natural gas liquids in 25 geologically defined areas thought to have potential for petroleum. This represented 13% of the expected undiscovered oil in the world. Of the estimated totals, more than half of the undiscovered oil resources were estimated to occur in just three geologic provinces—Arctic Alaska, the Amerasia Basin, and the East Greenland Rift Basins. More than 70% of the mean undiscovered oil resources was estimated to occur in five provinces: Arctic Alaska, Amerasia Basin, East Greenland Rift Basins, East Barents Basins, and West Greenland–East Canada. It was further estimated that approximately 84% of the oil and gas would occur offshore. The USGS did not consider economic factors such as the effects of permanent sea ice or oceanic water depth in its assessment of undiscovered oil and gas resources. This assessment was lower than a 2000 survey, which had included lands south of the Arctic Circle.
The Exclusive Economic Zone is a delineated offshore area, mostly to the west and north of Cuba, which, under international agreements, is owned by Cuba. This 112,000-square-kilometer zone has been divided into 59 exploration blocks. A 2004 joint partnership between a Spanish oil company and Cuba's state oil company (CUPET
) estimated Cuba's off-shore reserves to be able to produce ultimately between 4.6 and 9.3 billion barrels of crude oil.
The US Geological Survey (USGS) estimates that Cuba has resources up to 9 Goilbbl of oil. In October 2008, the Cuban government announced that it had discovered oil basins that would double its total oil resources to 20 Goilbbl. Note that, consistent with the definitions of reserves and resources as given in the above sections, at this stage (June 2009), given no commercial discoveries to date, all recoverable oil estimates in the Exclusive Economic Zone (EEZ) are prospective resources estimates and not reserves estimates.
Energy and resources:
Oil reservoir
A petroleum reservoir, or oil and gas reservoir, is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. The naturally occurring hydrocarbons, such as crude oil or natural gas, are trapped by overlying rock formations with lower permeability...
, including both producible and non-producible oil, is called oil in place
Oil In Place
Oil in place is the total hydrocarbon content of an oil reservoir and is often abbreviated STOOIP, which stands for Stock Tank Original Oil In Place, or STOIIP for Stock Tank Oil Initially In Place, referring to the oil in place before the commencement of production...
. However, because of reservoir characteristics
Reservoir engineering
Reservoir engineering is a branch of petroleum engineering that applies scientific principles to the drainage problems arising during the development and production of oil and gas reservoirs so as to obtain a high economic recovery....
and limitations in petroleum extraction technologies
Extraction of petroleum
The extraction of petroleum is the process by which usable petroleum is extracted and removed from the earth.-Locating the oil field:Geologists use seismic surveys to search for geological structures that may form oil reservoirs...
, only a fraction of this oil can be brought to the surface, and it is only this producible fraction that is considered to be reserves. The ratio of producible oil reserves to total oil in place for a given field is often referred to as the recovery factor. Recovery factors vary greatly among oil fields. The recovery factor of any particular field may change over time based on operating history and in response to changes in technology
Technology
Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes ;...
and economics
Economics
Economics is the social science that analyzes the production, distribution, and consumption of goods and services. The term economics comes from the Ancient Greek from + , hence "rules of the house"...
. The recovery factor may also rise over time if additional investment is made in enhanced oil recovery
Enhanced oil recovery
Enhanced Oil Recovery is a generic term for techniques for increasing the amount of crude oil that can be extracted from an oil field...
techniques such as gas injection, surfactants injection, water-flooding, or microbial enhanced oil recovery
Microbial enhanced oil recovery
Microbial Enhanced Oil Recovery is a biological based technology consisting in manipulating function or structure, or both, of microbial environments existing in oil reservoirs. The ultimate aim of MEOR is to improve the recovery of oil entrapped in porous media while increasing economic profits...
.
Based on data from OPEC
OPEC
OPEC is an intergovernmental organization of twelve developing countries made up of Algeria, Angola, Ecuador, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, the United Arab Emirates, and Venezuela. OPEC has maintained its headquarters in Vienna since 1965, and hosts regular meetings...
at the beginning of 2011 the highest proved oil reserves including non-conventional oil deposits are in Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...
(20 per cent of global reserves), Saudi Arabia
Energy in Saudi Arabia
Energy in Saudi Arabia describes energy and electricity production, consumption and export in Saudi Arabia.Saudi Arabia is one of the world's largest energy producers, pumping approximately of petroleum...
(18 %,of global reserves), Iran
Energy in Iran
Energy resources in Iran consist of the third largest oil reserves and the second largest natural gas reserves in the world. Iran is in a constant battle to use its energy resources more effectively in the face of subsidization and the need for technological advances in energy exploration and...
(9 %).
Because the geology
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
of the subsurface cannot be examined directly, indirect techniques
Exploration geophysics
Exploration geophysics is the applied branch of geophysics which uses surface methods to measure the physical properties of the subsurface Earth, in order to detect or infer the presence and position of ore minerals, hydrocarbons, geothermal reservoirs, groundwater reservoirs, and other geological...
must be used to estimate the size and recoverability of the resource. While new technologies
Reflection seismology
Reflection seismology is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismic source of energy, such as dynamite/Tovex, a specialized air gun or a...
have increased the accuracy of these techniques, significant uncertainties still remain. In general, most early estimates of the reserves of an oil field are conservative and tend to grow with time. This phenomenon is called reserves growth.
Many oil-producing nations do not reveal their reservoir engineering field data and instead provide unaudited claims for their oil reserves. The numbers disclosed by some national governments are suspected of being manipulated for political reasons.
Classifications
Society of Petroleum Engineers
The Society of Petroleum Engineers is a not-for-profit professional organization whose mission is to collect, disseminate, and exchange technical knowledge concerning the exploration, development and production of oil and gas resources and related technologies for the public benefit and to provide...
(SPE) and the World Petroleum Council (WPC) in 1997.
Proven reserves
Proven reserves are those reserves claimed to have a reasonable certainty (normally at least 90% confidence) of being recoverable under existing economic and political conditions, with existing technology. Industry specialists refer to this as P90 (i.e., having a 90% certainty of being produced). Proven reserves are also known in the industry as 1P.Proven reserves are further subdivided into "proven developed" (PD) and "proven undeveloped" (PUD). PD reserves are reserves that can be produced with existing wells and perforations, or from additional reservoirs where minimal additional investment (operating expense) is required. PUD reserves require additional capital investment (e.g., drilling new wells) to bring the oil to the surface.
Until December 2009 "1P" proven reserves
Proven reserves
Proven reserves, also called proved reserves, measured reserves, 1P, and Reserves, are business or political terms regarding fossil fuel energy sources....
were the only type the U.S. Securities and Exchange Commission allowed oil companies to report to investors. Companies listed on U.S. stock exchanges must substantiate their claims, but many governments and national oil companies do not disclose verifying data to support their claims. Since January 2010 the SEC now allows companies to also provide additional optional information declaring "2P" (both proven and probable) and "3P" (proven + probable + possible) provided the evaluation is verified by qualified third party consultants, though many companies choose to use 2P and 3P estimates only for internal purposes.
Unproven reserves
Probable reserves are attributed to known accumulations and claim a 50% confidence level of recovery. Industry specialists refer to them as "P50" (i.e., having a 50% certainty of being produced). These reserves are also referred to in the industry as "2P" (proven plus probable).
Possible reserves are attributed to known accumulations that have a less likely chance of being recovered than probable reserves. This term is often used for reserves which are claimed to have at least a 10% certainty of being produced ("P10"). Reasons for classifying reserves as possible include varying interpretations of geology, reserves not producible at commercial rates, uncertainty due to reserve infill (seepage from adjacent areas) and projected reserves based on future recovery methods. They are referred to in the industry as "3P" (proven plus probable plus possible).
Fraud and incompetence
In the early 1980s the Penn Square Bank
Penn Square Bank
Penn Square Bank was a small commercial bank located in the rear of the Penn Square Mall in Oklahoma City. The bank made its name in high-risk energy loans during the late 1970s and early 1980s Oklahoma and Texas oil boom. Between 1974 and 1982, the bank's assets increased more than 15 times to...
of Oklahoma engaged in wide scale lending to Oil and Gas groups with reserves used as collateral
Collateral
Collateral may refer to:* Collateral * Collateral -See also:* Collateral damage* Collateral Warranty* Collateral contract* Collateral ganglia* Collateral estoppel* Collateral source rule* Collateralized debt obligation...
for the loans. Sometimes the bank officers ignored the engineering advice about reserve size and value in order to book the loan profit. The bank resold many of the loans as 'loan participations' to larger banks like Continental Illinois, Seattle First, Michigan National
Michigan National Bank
Michigan National Bank was a bank founded in Lansing, Michigan, which was established on 31 December 1940 when Howard J Stoddard consolidated six Michigan banks: First National Bank and Trust Company of Grand Rapids, First National Trust and Savings Bank of Port Huron, Lansing National Bank,...
, and Chase Manhattan
Chase Manhattan Bank
JPMorgan Chase Bank, N.A., doing business as Chase, is a national bank that constitutes the consumer and commercial banking subsidiary of financial services firm JPMorgan Chase. The bank was known as Chase Manhattan Bank until it merged with J.P. Morgan & Co. in 2000...
, whose officers also sometimes ignored engineering advice. When the oil market busted, many of these loans were called, and the true nature of the reserves used as loan collateral was discovered by Federal Deposit Insurance Corporation
Federal Deposit Insurance Corporation
The Federal Deposit Insurance Corporation is a United States government corporation created by the Glass–Steagall Act of 1933. It provides deposit insurance, which guarantees the safety of deposits in member banks, currently up to $250,000 per depositor per bank. , the FDIC insures deposits at...
government investigators and creditors. Penn Square went bust, and Continental Illinois was the first Too Big to Fail
Too Big to Fail
Too Big to Fail is a television drama film in the United States broadcast on HBO on May 23, 2011. It is based on the non-fiction book Too Big to Fail by Andrew Ross Sorkin. The TV film was directed by Curtis Hanson...
bailout of the modern era.
Strategic petroleum reserves
Many countries maintain government-controlled oil reserves for both economic and national security reasons. According to the United States Energy Information AdministrationEnergy Information Administration
The U.S. Energy Information Administration is the statistical and analytical agency within the U.S. Department of Energy. EIA collects, analyzes, and disseminates independent and impartial energy information to promote sound policymaking, efficient markets, and public understanding of energy and...
, approximately 4.1 Goilbbl of oil are held in strategic reserves, of which 1.4 billion is government-controlled. These reserves are generally not counted when computing a nation's oil reserves.
Resources
American Association of Petroleum Geologists
The American Association of Petroleum Geologists is one of the world's largest professional geological societies with over 31,000 members as of 2007. The AAPG works to advance the science of geology , to promote technology, and to inspire high professional conduct...
(AAPG), and Society of Petroleum Evaluation Engineers (SPEE). It incorporates the 1997 definitions for reserves, but adds categories for contingent resources and prospective resources.
Contingent resources are those quantities of petroleum estimated, as of a given date, to be potentially recoverable from known accumulations, but the applied project(s) are not yet considered mature enough for commercial development due to one or more contingencies. Contingent resources may include, for example, projects for which there are currently no viable markets, or where commercial recovery is dependent on technology under development, or where evaluation of the accumulation is insufficient to clearly assess commerciality.
Prospective resources are those quantities of petroleum estimated, as of a given date, to be potentially recoverable from undiscovered accumulations by application of future development projects. Prospective resources have both an associated chance of discovery and a chance of development.
The United States Geological Survey
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...
uses the terms technically and economically recoverable resources when making its petroleum resource assessments. Technically recoverable resources represent that proportion of assessed in-place petroleum that may be recoverable using current recovery technology, without regard to cost. Economically recoverable resources are technically recoverable petroleum for which the costs of discovery, development, production, and transport, including a return to capital, can be recovered at a given market price.
"Unconventional resources" exist in petroleum accumulations that are pervasive throughout a large area. Examples include extra heavy oil
Heavy crude oil
Heavy crude oil or extra heavy crude oil is any type of crude oil which does not flow easily. It is referred to as "heavy" because its density or specific gravity is higher than that of light crude oil. Heavy crude oil has been defined as any liquid petroleum with an API gravity less than 20°.Extra...
, natural bitumen, and oil shale
Oil shale
Oil shale, an organic-rich fine-grained sedimentary rock, contains significant amounts of kerogen from which liquid hydrocarbons called shale oil can be produced...
deposits. Unlike "conventional resources", in which the petroleum is recovered through wellbores and typically requires minimal processing prior to sale, unconventional resources require specialized extraction technology to produce. For example, steam and/or solvents are used to mobilize bitumen for in-situ recovery. Moreover, the extracted petroleum may require significant processing prior to sale (e.g., bitumen upgraders). The total amount of unconventional oil resources in the world considerably exceeds the amount of conventional oil reserves, but are much more difficult and expensive to develop.
Estimation techniques
Oil In Place
Oil in place is the total hydrocarbon content of an oil reservoir and is often abbreviated STOOIP, which stands for Stock Tank Original Oil In Place, or STOIIP for Stock Tank Oil Initially In Place, referring to the oil in place before the commencement of production...
(OIP). Only a fraction of this oil can be recovered from a reservoir. This fraction is called the recovery factor. The portion that can be recovered is considered to be a reserve. The portion that is not recoverable is not included unless and until methods are implemented to produce it.
There are a number of different methods of calculating oil reserves. These methods can be grouped into three general categories: "volumetric", "material balance", and "production performance". Each method has its advantages and drawbacks.
Volumetric method
Volumetric methods attempt to determine the amount of oil in place by using the size of the reservoir as well as the physical properties of its rocks and fluids. Then a recovery factor is assumed, using assumptions from fields with similar characteristics. OIP is multiplied by the recovery factor to arrive at a reserve number. Current recovery factors for oil fields around the world typically range between 10 and 60 percent; some are over 80 percent. The wide variance is due largely to the diversity of fluid and reservoir characteristics for different deposits. The method is most useful early in the life of the reservoir, before significant production has occurred.Materials balance method
The materials balance method for an oil field uses an equation that relates the volume of oil, water and gas that has been produced from a reservoir and the change in reservoir pressure to calculate the remaining oil. It assumes that, as fluids from the reservoir are produced, there will be a change in the reservoir pressure that depends on the remaining volume of oil and gas. The method requires extensive pressure-volume-temperature analysis and an accurate pressure history of the field. It requires some production to occur (typically 5% to 10% of ultimate recovery), unless reliable pressure history can be used from a field with similar rock and fluid characteristics.Production decline curve method
The decline curve method uses production data to fit a decline curve and estimate future oil production. The three most common forms of decline curves are exponential, hyperbolic, and harmonic. It is assumed that the production will decline on a reasonably smooth curve, and so allowances must be made for wells shut in and production restrictions. The curve can be expressed mathematically or plotted on a graph to estimate future production. It has the advantage of (implicitly) including all reservoir characteristics. It requires a sufficient history to establish a statistically significant trend, ideally when production is not curtailed by regulatory or other artificial conditions.Reserves growth
Experience shows that initial estimates of the size of newly discovered oil fields are usually too low. As years pass, successive estimates of the ultimate recovery of fields tend to increase. The term reserve growth refers to the typical increases in estimated ultimate recovery that occur as oil fields are developed and produced.Estimated reserves by country
| Country | Reserves | Production | Reserve life 1 | ||
|---|---|---|---|---|---|
| 109 bbl | 109 m3 | 106 bbl/d | 103 m3/d | years | |
| Venezuela Oil reserves in Venezuela The proven oil reserves in Venezuela are claimed to be the largest in the world, according to an announcement in early 2011 by President Hugo Chavez and the Venezuelan government. The reported proven reserves reach , surpassing that of the previous long-term world leader, Saudi Arabia... |
296.5 Goilbbl | 2.1 Moilbbl | 129 | ||
| Saudi Arabia Oil reserves in Saudi Arabia Proven oil reserves in Saudi Arabia are the second largest claimed in the world, estimated to be including 2.5 Gbbl in the Saudi-Kuwaiti neutral zone. These reserves were the largest in the world until Venezuela announced they had increased their proven reserves to 297 Gbbl in January 2011... |
264.52 Goilbbl | 8.9 Moilbbl | 81 | ||
| Canada Oil reserves in Canada Oil reserves in Canada were estimated at in 2007. This figure includes oil sands reserves which are estimated by government regulators to be economically producible at current prices using current technology. According to this figure, Canada's reserves are third only to Venezuela and Saudi... |
175 Goilbbl | 2.7 Moilbbl | 178 | ||
| Iran Oil reserves in Iran Oil reserves in Iran, according to its government, rank third largest in the world at approximately as of 2007, although it ranks second if Canadian reserves of unconventional oil are excluded. This is roughly 10% of the world's total proven petroleum reserves. Iran is the world's fourth largest... |
151.2 Goilbbl | 4.1 Moilbbl | 101 | ||
| Iraq Oil reserves in Iraq Oil reserves in Iraq will be the largest in the world according to recent geological surveys and seismic data. The Iraqi government has stated that new exploration showed Iraq has the world’s largest proven oil reserves, with more than 350 billion barrels... |
143.1 Goilbbl | 2.4 Moilbbl | 163 | ||
| Kuwait Oil reserves in Kuwait Oil reserves in Kuwait make up 8% of the oil reserves in the world. Kuwait is OPEC's third largest oil producer and claims to hold approximately . This includes half of the in the Saudi-Kuwaiti neutral zone which Kuwait shares with Saudi Arabia... |
101.5 Goilbbl | 2.3 Moilbbl | 121 | ||
| United Arab Emirates Oil reserves in the United Arab Emirates Oil reserves in the United Arab Emirates, according to its government, are about , almost as big as Kuwait's claimed reserves. Of the emirates, Abu Dhabi has most of the oil with while Dubai has and Sharjah has . Most of the oil is in the Zakum field which is the third largest in the Middle East... |
97.8 Goilbbl | 2.4 Moilbbl | 112 | ||
| Russia Oil reserves in Russia There are several different estimates of proven oil reserves in Russia. Most estimates include only Western Siberian reserves, exploited since the 1970s and supplying two-thirds of Russian oil, and not potentially huge reserves elsewhere... |
74.2 Goilbbl | 9.7 Moilbbl | 21 | ||
| Libya Oil reserves in Libya Oil reserves in Libya are the largest in Africa and the eighth largest in the world with as of 2010. Oil production was as of 2010, giving Libya 77 years of reserves at current production rates if no new reserves were to be found... |
47 Goilbbl | 1.7 Moilbbl | 76 | ||
| Nigeria Oil reserves in Nigeria Although Libya has more reserves, there were of proven oil reserves in Nigeria as of 2007, ranking the country as the largest oil producer in Africa and the 11th largest in the world, averaging in 2006. At current rates this would be 43 years of supply if no new oil was found... |
37 Goilbbl | 2.5 Moilbbl | 41 | ||
| Kazakhstan | 30 Goilbbl | 1.5 Moilbbl | 55 | ||
| Qatar | 25.41 Goilbbl | 1.1 Moilbbl | 63 | ||
| China | 20.35 Goilbbl | 4.1 Moilbbl | 14 | ||
| United States Oil reserves in the United States Proven oil reserves in the United States are , excluding the Strategic Petroleum Reserve. The U.S. Department of the Interior estimates the total volume of undiscovered, technically recoverable prospective resources in all areas of the United States, including the Federal Outer Continental Shelf,... |
19.12 Goilbbl | 5.5 Moilbbl | 10 | ||
| Angola | 13.5 Goilbbl | 1.9 Moilbbl | 19 | ||
| Algeria | 13.42 Goilbbl | 1.7 Moilbbl | 22 | ||
| Brazil | 13.2 Goilbbl | 2.1 Moilbbl | 17 | ||
| Total of top seventeen reserves | 1324 Goilbbl | 56.7 Moilbbl | 64 | ||
Notes:
|
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OPEC countries
There are doubts about the reliability of official OPEC reserves estimates, which are not provided with any form of audit or verification that meet external reporting standards.Since a system of country production quotas was introduced in the 1980s, partly based on reserves levels, there have been dramatic increases in reported reserves among OPEC producers. In 1983, Kuwait increased its proven reserves from 67 Goilbbl to 92 Goilbbl. In 1985–86, the UAE almost tripled its reserves from 33 Goilbbl to 97 Goilbbl. Saudi Arabia raised its reported reserve number in 1988 by 50%. In 2001–02, Iran raised its proven reserves by some 30% to 130 Goilbbl, which advanced it to second place in reserves and ahead of Iraq. Iran denied accusations of a political motive behind the readjustment, attributing the increase instead to a combination of new discoveries and improved recovery. No details were offered of how any of the upgrades were arrived at.
The following table illustrates these rises.
| Declared reserves of major Opec Producers (billion of barrels) | ||||||||
| BP Statistical Review - June 2009 | ||||||||
| OPEC Annual Statistical Bulletin 2010/2011 | ||||||||
| Year | Iran Iran Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia... |
Iraq Iraq Iraq ; officially the Republic of Iraq is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert.... |
Kuwait Kuwait The State of Kuwait is a sovereign Arab state situated in the north-east of the Arabian Peninsula in Western Asia. It is bordered by Saudi Arabia to the south at Khafji, and Iraq to the north at Basra. It lies on the north-western shore of the Persian Gulf. The name Kuwait is derived from the... |
Saudi Arabia Saudi Arabia The Kingdom of Saudi Arabia , commonly known in British English as Saudi Arabia and in Arabic as as-Sa‘ūdiyyah , is the largest state in Western Asia by land area, constituting the bulk of the Arabian Peninsula, and the second-largest in the Arab World... |
UAE | Venezuela Venezuela Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south... |
Libya Libya Libya is an African country in the Maghreb region of North Africa bordered by the Mediterranean Sea to the north, Egypt to the east, Sudan to the southeast, Chad and Niger to the south, and Algeria and Tunisia to the west.... |
Nigeria Nigeria Nigeria , officially the Federal Republic of Nigeria, is a federal constitutional republic comprising 36 states and its Federal Capital Territory, Abuja. The country is located in West Africa and shares land borders with the Republic of Benin in the west, Chad and Cameroon in the east, and Niger in... |
| 1980 | 58.3 | 30.0 | 67.9 | 168.0 | 30.4 | 19.5 | 20.3 | 16.7 |
| 1981 | 57.0 | 32.0 | 67.7 | 167.9 | 32.2 | 19.9 | 22.6 | 16.5 |
| 1982 | 56.1 | 59.0 | 67.2 | 165.5 | 32.4 | 24.9 | 22.2 | 16.8 |
| 1983 | 55.3 | 65.0 | 67.0 | 168.8 | 32.3 | 25.9 | 21.8 | 16.6 |
| 1984 | 58.9 | 65.0 | 92.7 | 171.7 | 32.5 | 28.0 | 21.4 | 16.7 |
| 1985 | 59.0 | 65.0 | 92.5 | 171.5 | 33.0 | 54.5 | 21.3 | 16.6 |
| 1986 | 92.9 | 72.0 | 94.5 | 169.7 | 97.2 | 55.5 | 22.8 | 16.1 |
| 1987 | 92.9 | 100.0 | 94.5 | 169.6 | 98.1 | 58.1 | 22.8 | 16.0 |
| 1988 | 92.9 | 100.0 | 94.5 | 255.0 | 98.1 | 58.5 | 22.8 | 16.0 |
| 1989 | 92.9 | 100.0 | 97.1 | 260.1 | 98.1 | 59.0 | 22.8 | 16.0 |
| 1990 | 92.9 | 100.0 | 97.0 | 260.3 | 98.1 | 60.1 | 22.8 | 17.1 |
| 1991 | 92.9 | 100.0 | 96.5 | 260.9 | 98.1 | 62.6 | 22.8 | 20.0 |
| 1992 | 92.9 | 100.0 | 96.5 | 261.2 | 98.1 | 63.3 | 22.8 | 21.0 |
| 1993 | 92.9 | 100.0 | 96.5 | 261.4 | 98.1 | 64.4 | 22.8 | 21.0 |
| 1994 | 94.3 | 100.0 | 96.5 | 261.4 | 98.1 | 64.9 | 22.8 | 21.0 |
| 1995 | 93.7 | 100.0 | 96.5 | 261.5 | 98.1 | 66.3 | 29.5 | 20.8 |
| 1996 | 92.6 | 112.0 | 96.5 | 261.4 | 97.8 | 72.7 | 29.5 | 20.8 |
| 1997 | 92.6 | 112.5 | 96.5 | 261.5 | 97.8 | 74.9 | 29.5 | 20.8 |
| 1998 | 93.7 | 112.5 | 96.5 | 261.5 | 97.8 | 76.1 | 29.5 | 22.5 |
| 1999 | 93.1 | 112.5 | 96.5 | 262.8 | 97.8 | 76.8 | 29.5 | 29.0 |
| 2000 | 99.5 | 112.5 | 96.5 | 262.8 | 97.8 | 76.8 | 36.0 | 29.0 |
| 2001 | 99.1 | 115.0 | 96.5 | 262.7 | 97.8 | 77.7 | 36.0 | 31.5 |
| 2002 | 130.7 | 115.0 | 96.5 | 262.8 | 97.8 | 77.3 | 36.0 | 34.3 |
| 2003 | 133.3 | 115.0 | 99.0 | 262.7 | 97.8 | 77.2 | 39.1 | 35.3 |
| 2004 | 132.7 | 115.0 | 101.5 | 264.3 | 97.8 | 79.7 | 39.1 | 35.9 |
| 2005 | 137.5 | 115.0 | 101.5 | 264.2 | 97.8 | 80.0 | 41.5 | 36.2 |
| 2006 | 138.4 | 115.0 | 101.5 | 264.3 | 97.8 | 87.3 | 41.5 | 36.2 |
| 2007 | 138.2 | 115.0 | 101.5 | 264.2 | 97.8 | 99.4 | 43.7 | 36.2 |
| 2008 | 137.6 | 115.0 | 101.5 | 264.1 | 97.8 | 172.3 | 43.7 | 36.2 |
| 2009 | 137.0 | 115.0 | 101.5 | 264.6 | 97.8 | 211.1 | 46.4 | 36.2 |
| 2010 | 151.2 | 143.1 | 101.5 | 264.5 | 97.8 | 296.5 | 47.1 | 36.2 |
The sudden revisions in OPEC reserves, totaling nearly 300 bn barrels, have been much debated. Some of it is defended partly by the shift in ownership of reserves away from international oil companies, some of whom were obliged to report reserves under conservative US Securities and Exchange Commission rules. The most prominent explanation of the revisions is prompted by a change in OPEC rules which set production quotas (partly) on reserves. In any event, the revisions in official data had little to do with the actual discovery of new reserves.
Total reserves in many OPEC countries hardly changed in the 1990s. Official reserves in Kuwait, for example, were unchanged at 96.5 Goilbbl (including its share of the Neutral Zone) from 1991 to 2002, even though the country produced more than 8 Goilbbl and did not make any important new discoveries during that period. The case of Saudi Arabia is also striking, with proven reserves estimated at between 260 and 264 Goilbbl in the past 18 years, a variation of less than 2%, while extracting approximately 60 Goilbbl during this period.
Sadad al-Huseini, former head of exploration and production at Saudi Aramco, estimates 300 Goilbbl of the world's 1200 Goilbbl of proven reserves should be recategorized as speculative resources, though he did not specify which countries had inflated their reserves. Dr. Ali Samsam Bakhtiari, a former senior expert of the National Iranian Oil Company
National Iranian Oil Company
The National Iranian Oil Company , a government-owned corporation under the direction of the Ministry of Petroleum of Iran, is an oil and natural gas producer and distributor headquartered in Tehran. It was established in 1948...
, has estimated that Iran, Iraq, Kuwait, Saudi Arabia and the United Arab Emirates have overstated reserves by a combined 320–390bn barrels and has said, "As for Iran, the usually accepted official 132 Goilbbl is almost one hundred billion over any realistic assay." Petroleum Intelligence Weekly reported that official confidential Kuwaiti documents estimate reserves of Kuwait were only 48 Goilbbl, of which half were proven and half were possible. The combined value of proven and possible is half of the official public estimate of proven reserves.
In July 2011, OPEC's Annual Statistical Review showed Venezuela's reserves to be larger than Saudi Arabia's.
Arctic prospective resources
Miscellaneous prospective resources
In October 2009, the USGS updated the Orinoco tar sands (Venezuela) value to 513 Goilbbl.The Exclusive Economic Zone is a delineated offshore area, mostly to the west and north of Cuba, which, under international agreements, is owned by Cuba. This 112,000-square-kilometer zone has been divided into 59 exploration blocks. A 2004 joint partnership between a Spanish oil company and Cuba's state oil company (CUPET
Cupet
Cupet is Cuba's state oil company. The company is involved in the extraction of petroleum deposits, refining, and distributing petroleum products. In conjunction with the conglomerate Cimex, it operates a chain of filling stations selling gasoline in convertible pesos.The extraction is based in...
) estimated Cuba's off-shore reserves to be able to produce ultimately between 4.6 and 9.3 billion barrels of crude oil.
The US Geological Survey (USGS) estimates that Cuba has resources up to 9 Goilbbl of oil. In October 2008, the Cuban government announced that it had discovered oil basins that would double its total oil resources to 20 Goilbbl. Note that, consistent with the definitions of reserves and resources as given in the above sections, at this stage (June 2009), given no commercial discoveries to date, all recoverable oil estimates in the Exclusive Economic Zone (EEZ) are prospective resources estimates and not reserves estimates.
See also
- Global strategic petroleum reservesGlobal strategic petroleum reservesGlobal strategic petroleum reserves refer to crude oil inventories held by the government of a particular country, as well as private industry, for the purpose of providing economic and national security during an energy crisis...
- Oil explorationOil explorationHydrocarbon exploration is the search by petroleum geologists and geophysicists for hydrocarbon deposits beneath the Earth's surface, such as oil and natural gas...
- Peak oilPeak oilPeak oil is the point in time when the maximum rate of global petroleum extraction is reached, after which the rate of production enters terminal decline. This concept is based on the observed production rates of individual oil wells, projected reserves and the combined production rate of a field...
- Petroleum IndustryPetroleum industryThe petroleum industry includes the global processes of exploration, extraction, refining, transporting , and marketing petroleum products. The largest volume products of the industry are fuel oil and gasoline...
- Strategic Petroleum ReserveStrategic Petroleum ReserveThe Strategic Petroleum Reserve is an emergency fuel storage of oil maintained by the United States Department of Energy.- United States :The US SPR is the largest emergency supply in the world with the current capacity to hold up to ....
Energy and resources:
- Energy securityEnergy securityEnergy security is a term for an association between national security and the availability of natural resources for energy consumption. Access to cheap energy has become essential to the functioning of modern economies. However, the uneven distribution of energy supplies among countries has led...
- World energy resources and consumptionWorld energy resources and consumption]World energy consumption in 2010: over 5% growthEnergy markets have combined crisis recovery and strong industry dynamism. Energy consumption in the G20 soared by more than 5% in 2010, after the slight decrease of 2009. This strong increase is the result of two converging trends...
- List of countries by natural gas proven reserves
External links
- OPEC Annual Statistical Bulletin
- Energy Supply page on the Global Education Project web site, including many charts and graphs on the world's energy supply and use
- Oil reserves (most recent) by country