The authors of this report summarize a geology-based assessment of undiscovered conventional oil and gas resources of priority geologic provinces of the world, completed between 2009 and 2011 as part of the U.S. Geological Survey (USGS) World Petroleum Resources Project (fig. 1). One hundred seventy-one geologic provinces were assessed in this study (exclusive of provinces of the United States), which represent a complete reassessment of the world since the last report was published in 2000 (U.S. Geological Survey World Energy Assessment Team, 2000). The present report includes the recent oil and gas assessment of geologic provinces north of
the Arctic Circle (U.S. Geological Survey Circum-Arctic Resource Appraisal Assessment Team, 2008). However, not all potential oil- and gas-bearing provinces of the world were assessed in the present study.
The methodology for the assessment included a complete geologic framework description for each province based mainly on published literature, and the definition of petroleum systems and assessment units (AU) within these systems. In this study, 313 AUs were defined and assessed for undiscovered oil and gas accumulations. Exploration and discovery history was a critical part of the methodology to determine sizes and numbers of undiscovered accumulations. In those AUs with few or no discoveries, geologic and production analogs were used as a partial guide to estimate sizes and numbers of undiscovered oil and gas accumulations, using a database developed by the USGS following the 2000 assessment (Charpentier and others, 2008). Each AU was assessed for undiscovered oil and nonassociated gas accumulations, and co-product ratios were used to calculate the volumes of associated gas (gas in oil fields) and volumes of natural gas liquids. This assessment is for conventional oil and gas resources only; unconventional resource assessments (heavy oil, tar sands, shale gas, shale oil, tight gas, coalbed gas) for priority areas of the world are being completed in an ongoing but separate USGS study.
The USGS assessed undiscovered conventional oil and gas resources in 313 AUs within 171 geologic provinces. In this report the results are presented by geographic region, which correspond to the eight regions used by the U.S. Geological Survey World Energy Assessment Team (2000) (table 1). For undiscovered, technically recoverable resources, the mean totals for the world are as follows:
(1) 565,298 million barrels of oil (MMBO);
(2) 5,605,626 billion cubic feet of gas (BCFG);
and (3) 166,668 million barrels (MMBNGL) of natural gas liquids.
The ranges of resource estimates (between the 95 and 5 fractiles) reflect the geologic uncertainty in the assessment process (table 1). The assessment results indicate that about 75 percent of the undiscovered conventional oil of the world is in four regions:
(1) South America and Caribbean,
(2) sub-Saharan Africa,
(3) Middle East and North Africa, and
(4) the Arctic provinces portion of North America.
Significant undiscovered conventional gas resources remain in all of the world’s regions (table 1).
Regions 0 and 1 (29 assessed provinces) encompass geologic provinces within countries of the former Soviet Union and include many provinces of the Arctic (fig. 1). Of the mean undiscovered estimate of 66 billion barrels of oil (BBO) in this region, about 43 percent
is estimated to be in Arctic provinces. This region also contains significant gas resources [mean of 1,623 trillion cubic feet of gas (TCFG)], about 58 percent of which is estimated to be in three Arctic AUs: South Kara Sea AU (622 TCFG); South Barents Basin AU (187 TCFG), and North Barents Basin AU (127 TCFG).
Region 2 (26 assessed provinces), the Middle East and North Africa, includes the Zagros Fold Belt of Iran, Arabian Peninsula, southern Turkey, and geologic provinces of North Africa from Egypt to Morocco. This region is estimated to contain a mean of 111 BBO, about 60 percent (65 BBO) of which is estimated to be in the Zagros and Mesopotamian provinces. This region is estimated to contain a conventional gas resource mean of 941 TCFG, about 60 percent (566 TCFG)
of which is estimated to be in the Zagros Fold Belt and the offshore areas of the Red Sea Basin, Levantine Basin, and Nile Delta provinces.
Region 3 (39 assessed provinces), Asia and Pacific, includes geologic provinces of China, Vietnam, Thailand, Malaysia, Cambodia, Philippines, Brunei, Indonesia, Papua New Guinea, East Timor, Australia, and New Zealand. Of the total mean undiscovered oil resources of 48 BBO, about 33 percent is estimated to be in China provinces (15.7 BBO), and 10 percent is in Australian provinces (5 BBO). Other significant oil resources are in offshore Brunei (3.6 BBO), Kutei Basin (3 BBO), and South China Sea (2.5 BBO) provinces. Of the undiscovered mean total of 738 TCFG, about 45 percent (335 TCFG) is in provinces of Australia (227 TCFG) and China (108 TCFG). The rest of the gas resource is distributed across the other provinces of Southeast Asia.
Region 4 (6 assessed provinces) includes Europe and several Arctic provinces. Of the mean of 9.9 BBO of undiscovered oil, about 50 percent (5 BBO) is estimated to be in the North Sea province. Of the undiscovered gas resource of 149 TCFG, the Arctic provinces are estimated to contain about 40 percent (58 TCFG). Significant undiscovered gas resources are estimated to be in the Norwegian continental margin, Provencal Basin, and Po Basin provinces.
Region 5 (21 assessed provinces), North America exclusive of the United States, includes Mexico, Canada, and several Arctic provinces. Of the mean oil resource of 83 BBO, about 75 percent (61 BBO) is estimated to be in Arctic provinces, and 23 percent (19 BBO) is estimated to be in Mexican Gulf provinces. In this region about 83 percent (459 TCFG) of the undiscovered conventional gas is in the Arctic provinces.
Region 6 (31 assessed provinces) includes South America and the Caribbean area. Of the mean estimate of 126 BBO in this region, about 44 percent (55.6 BBO) is estimated to be in offshore subsalt reservoirs in the Santos, Campos, and Espirito Santo basin provinces. Other significant mean oil resources are estimated to be in the Guyana−Suriname Basin (12 BBO), Santos Basin (11 BBO), Falklands (5.3 BBO), and Campos Basin (3.7 BBO) provinces. Undiscovered gas resources are less concentrated and are distributed among many provinces.
Region 7 (13 assessed provinces), sub-Saharan Africa, is estimated to contain a mean 115 BBO, of which about 75 percent is estimated to be in coastal provinces related to the opening of the Atlantic Ocean, such as Senegal, Gulf of Guinea, West African Coastal, and West-Central Coastal provinces. Of the undiscovered gas resource mean of 744 TCFG, more than half is estimated to be in provinces of offshore east Africa, including those offshore Tanzania, Mozambique, Madagascar, and Seychelles.
Region 8 (6 assessed provinces), South Asia, includes India, Pakistan, Afghanistan, Bangladesh, and Burma. Of the mean of 5.9 BBO, about 1.8 BBO is estimated to be in the Central Burma Basin province and 1.4 BBO is in the Bombay province. Of the undiscovered gas resource of 159 TCFG, about 39 percent (62 TCFG) of the undiscovered gas resource is in the three provinces of offshore eastern India. Although unconventional oil and gas resources, such as heavy oil, tar sands, shale gas, shale oil, tight gas, and coalbed gas, are not included in this study, unconventional resource volumes can be truly significant. For example, the mean estimate for recoverable heavy oil from the Orinoco Oil Belt in Venezuela alone is 513 BBO (U.S. Geological Survey Orinoco Oil Belt Assessment Team, 2009), compared to mean conventional resources of 565 BBO for 171 provinces reported in this study.
USGS World Petroleum Assessment 2000