In the evaluation of undiscovered conventional oil and gas resources, play was taken as the basic evaluation unit^{[9, 10, 11]}. Different evaluation methods were adopted based on different exploration maturities and different data available levels. The selection of parameters for all evaluation methods were based on comprehensive geological evaluation. For the evaluation units of high exploration maturity with more than 6 oil or gas fields discovered, the discovery process method was used for the evaluation. For the China National Petroleum Corporation Assets, trap summation method was adopted. For the evaluation units of medium exploration maturity with less than 6 oil and gas fields, subjective probability method based on geological analysis was used. Volumetric analogy method was used for evaluation units that did not have any oil or gas discoveries or had little data available. Finally, Monte Carlo simulation method was used to add and summarize the evaluation results of different evaluation units with different evaluation methods. The evaluation results were expressed in terms of probability. The confidence levels from high to low were 95%, 50%, 5% and Mean^{[10, 11, 12]}.

The conventional reserve growth of discovered oil and gas fields refers to the newly-recovered conventional recoverable reserves in the entire life cycle of evaluation and development since the discovery of oil and gas fields due to appraisal, technological advances, changes in calculation methods, and political and economic factors. About 70% of the world's annual increase of conventional recoverable reserves comes from the reserves growth of discovered oil and gas fields ^{[12, 13, 14]}. Since 2P (Proved and Probable) reserve data of individual oil and gas fields in consecutive years cannot be obtained, it is difficult to establish a continuous reserve growth function based on an oil field. Therefore, the segmented cumulative multiplication method was used to obtain cumulative growth factors of different oil and gas fields over 30 consecutive years, and a model for oil and gas reserves growth was established (Fig. 1). The growth potential of discovered oil and gas fields in different regions were assessed by using their own reserve growth models^[12]. This kind of evaluation is more reasonable. However, the USGS uses only the North American model to predict the reserve growth of the world^[15], the reliability is poor.

Fig. 1.

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	Fig. 1. Reserves growth curve of discovered oil and gas fields applicable to different regions.

In the evaluation of global unconventional oil and gas resources, basins were divided into basins for general evaluation, detailed evaluation and key evaluation based on the detailed level of basin data, resource types, maturity of exploration and development, evaluation requirements, and applicability of evaluation techniques. The parametric probability method, GIS (Geographic Information System) spatial graph interpolation method, genesis-constraint volume method and hyperbolic exponential decline method were used for evaluation. The basins for general evaluation are mostly basins with low maturity of exploration and development and a lack of basic data and basic maps, and they are uniformly evaluated by the parameter probability method. The basins for detailed evaluation are basins with exploration and development activities, rich basic geological data and little production data from production wells; the basins for key evaluation are basins with active exploration and commercial development, rich basic geological data, large scale of resources and detailed production data of production wells. For detailed evaluation and key evaluation basins with unconventional reservoir-controlled type, such as heavy oil, oil sands, oil shale, tight gas, and coal bed methane, GIS spatial graphic interpolation method was used for the evaluation. Besides, comprehensive evaluation should be performed for key evaluation basins based on the resource abundance, recoverability and economy to sort out favorable blocks. For detailed evaluation and key evaluation basins with mainly source-controlled resources such as tight oil and shale gas, genesis-constraint volume method was used for the evaluation. For key basins with a high maturity of exploration and development and detailed development data such as well production, the effective evaluation areas were determined using basic geological parameter mapping and evaluated by the hyperbolic exponential decline method, and finally the ultimate recovery of the favorable blocks was calculated^[16].

The remaining recoverable 2P reserves of oil and gas are 4212.6× 10⁸ t, of which oil reserves are 2055.0× 10⁸ t, accounting for 48.8%; condensate oil reserves are 197.6× 10⁸ t, accounting for 4.7%; and natural gas reserves are 236.9× 10¹² m³, accounting for 46.5%. They are mainly distributed in the Middle East (45.3%), followed by Central Asia - Russia (19.7%) and Central and South America (15.1%).

2.1.1. Distribution in different countries

The remaining recoverable 2P reserves of oil and gas are distributed in 82 countries (excluding China), among which Russia, Saudi Arabia, Iran, and Venezuela account for 14.4%, 12.4%, 11.8%, and 11.5% of the world total respectively. Oil is mainly concentrated in Saudi Arabia and Venezuela, accounting for 21.1% and 20.7% of the world respectively. Natural gas is mainly concentrated in Russia and Iran, accounting for 23.0% and 21.1% of the world total respectively (Fig. 2 and Table 1).

Fig. 2.

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	Fig. 2. Histogram of remaining recoverable 2P reserves of oil and gas in major countries.

Table 1

Table 1

Table 1 Statistics of remaining recoverable 2P reserves of oil and gas in major countries. Countries Remaining recoverable 2P reserves of oil and gas/108 t Proportion of oil/% Proportion of condensate oil/% Proportion of natural gas/% Russia 572.4 29.8 3.8 66.4 Saudi Arabia 495.2 85.3 3.1 11.6 Iran 470.0 33.9 9.0 57.1 Venezuela 456.8 90.8 0.9 8.3 Qatar 287.3 5.0 13.6 81.4 Iraq 253.9 88.4 0.5 11.1 Turkmenistan 136.5 2.0 1.1 96.9 Kuwait 111.3 83.3 5.1 11.6 Brazil 107.3 78.9 3.1 18.0 United Arab Emirates 105.6 66.9 6.6 26.5

Table 1 Statistics of remaining recoverable 2P reserves of oil and gas in major countries.

Russia's remaining recoverable 2P reserves of oil and gas are 572.4× 10⁸ t, of which oil reserves accounts for 29.8%, condensate oil reserves accounts for 3.8% and natural gas reserves accounts for 66.4%. The remaining recoverable 2P reserves of oil and gas in Saudi Arabia are 495.2× 10⁸ t, of which oil, condensate oil and natural gas account for 85.3%, 3.1% and 11.6% respectively. The remaining recoverable 2P reserves of oil and gas of Iran are 470.0× 10⁸ t, of which oil, condensate oil and natural gas account for 33.9%, 9.0% and 57.1% respectively. The remaining recoverable 2P reserves of oil and gas in Venezuela are 456.8× 10⁸ t, of which oil and natural gas occupy 90.8% and 8.3% respectively.

2.1.2. Distribution in basins

The remaining recoverable 2P reserves of oil and gas are mainly distributed in 38 basins (excluding China). The remaining recoverable 2P reserves of oil and gas in the Arabian Basin, the Eastern Venezuelan Basin, and the West Siberian Basin account for 58.9% of the total global remaining recoverable 2P reserves of oil and gas (Fig. 3 and Table 2).

Fig. 3.

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	Fig. 3. Histogram of remaining recoverable 2P reserves of oil and gas in major basins.

Table 2

Table 2

Table 2 Statistics of remaining recoverable 2P reserves of oil and gas in major basins. Basin Remaining recoverable 2P reserves of oil and gas/108 t Proportion of oil/% Proportion of condensate oil/% Proportion of natural gas/% Arabian 1 530.9 53.1 6.4 40.5 Eastern Venezuelan 412.6 92.9 0.8 6.3 Western Siberian 403.3 28.1 3.1 68.8 Zagros 334.9 52.9 3.8 43.3 Amu Darya 148.6 0.7 1.7 97.6 Niger Delta 96.3 45.9 5.9 48.2 Precaspian 77.0 39.7 8.8 51.5 Santos 64.1 78.6 3.1 18.3 Ghadames 45.8 29.6 5.3 65.1 Volga-Ural 37.9 72.5 2.4 25.1

Table 2 Statistics of remaining recoverable 2P reserves of oil and gas in major basins.

The remaining recoverable 2P reserves of oil and gas in the Arabian Basin are 1 530.9× 10⁸ t, of which oil, condensate oil and natural gas reserves account for 53.1%, 6.4% and 40.5% respectively. The remaining recoverable 2P reserves of oil and gas in the eastern Venezuelan Basin are 412.6× 10⁸ t, of which oil, condensate oil and natural gas occupy 92.9%, 0.8% and 6.3% respectively. The remaining recoverable 2P reserves of oil and gas in the West Siberian Basin are 403.3× 10⁸ t, of which oil, condensate oil and natural gas take up 28.1%, 3.1% and 68.8% respectively.

2.1.3. Distribution onshore and offshore

The remaining 2P recoverable oil and gas reserves of onshore are 2 371.6× 10⁸ t, of which oil, condensate oil and natural gas reserves are 1 136.0× 10⁸ t (accounting for 47.9%), 116.2× 10⁸ t (accounting for 4.9%) and 132.3× 10 ¹² m³ (accounting for 47.2%) respectively. The remaining 2P recoverable oil and gas reserves of offshore are 1 840.9× 10⁸ t, of which oil, condensate oil and natural gas reserves are 854.2× 10⁸ t (accounting for 46.4 %), 97.6× 10⁸ t (accounting for 5.3%) and 105.4× 10¹² m³ (accounting for 48.3%). The remaining 2P recoverable reserves of onshore and offshore account for 56.3% and 43.7% of the total, respectively (Fig. 4).

Fig. 4.

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	Fig. 4. Distribution histogram of remaining 2P recoverable oil and gas reserves onshore and offshore in major basins of the world.

2.1.4. Distribution in different lithology of reservoirs

The remaining 2P recoverable reserves of oil and gas in the world are mainly distributed in the reservoirs of clastic rock (52.1%) and carbonate rock (47.5%). The remaining 2P recoverable reserves of oil and gas in basement and other types of reservoirs account for only 0.4%.

The remaining 2P recoverable reserves in clastic reservoirs are 2 194.7× 10⁸ t, which are mainly distributed in 18 basins in eastern Venezuelan basin, Western Siberian and Arabian basin (Fig. 5), of which oil, condensate oil and natural gas reserves account for 52.0%, 3.7% and 44.3%.

Fig. 5.

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	Fig. 5. Histogram of remaining recoverable 2P reserves of oil and gas in different lithology of major basins in the world.

The remaining 2P recoverable reserves in carbonate reservoirs are 2 000.9× 10⁸ t, and are mainly distributed in 12 basins such as Arabia and Zagros (Fig. 5), of which oil, condensate and natural gas reserves account for 50.4%, 5.2% and 44.4% respectively.

In the next 30 years, the world’ s increase in recoverable reserves of discovered oil and gas fields will be 1 531.7× 10⁸ t, of which oil, condensate oil and natural gas reserves are 708.7× 10⁸ t (46.3%), 72.8× 10⁸ t (4.8%) and 90.5× 10¹² m³ (48.9%) respectively. The reserves in the Middle East have the largest increase, accounting for 33.7% of the global total, followed by Central Asia-Russia and Africa, which account for 22.7% and 14.4% of the global total respectively. The reserves in Asia- Pacific, North America, Central Asia, and Central and South America have similar growth potential. The reserves in Europe have the lowest growth potential.

2.2.1. Distribution in different countries

Russia has the largest reserve growth potential in discovered oil and gas fields, accounting for 16.8% of the global total, of which the increase in oil reserves is 10.67× 10⁹ t, and the increase in natural gas reserves is 5.7% higher than that of oil. Iran and Saudi Arabia have similar growth potential of oil and gas reserves, accounting for 10.0% and 9.8% of the global total, respectively. Qatar is dominated by the increase in natural gas reserves, accounting for 6.2% of the global total. The United States and Venezuela are dominated by the growth in oil reserves, accounting for 5.9% and 5.2% of the global total, respectively (Fig. 6 and Table 3).

Fig. 6.

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	Fig. 6. Future recoverable reserves growth of discovered oil and gas fields in major countries of the world.

Table 3

Table 3

Table 3 Statistics of future reserves growth of discovered oil and gas fields in major countries of the world. Countries Future reserves growth of discovered oil and gas fields/108 t Proportion of oil/% Proportion of condensate oil/% Proportion of natural gas/% Russia 234.0 45.6 3.1 51.3 Iran 139.7 31.3 8.9 59.8 Saudi Arabia 136.8 75.4 4.7 19.9 Qatar 86.1 4.5 13.4 82.1 United States 82.5 62.1 4.3 33.6 Venezuela 72.6 78.6 1.4 20.0 Iraq 62.0 78.9 0.6 20.5 Nigeria 61.7 50.7 3.5 45.8 Turkmenistan 53.4 4.6 1.3 94.1 Libya 41.6 68.3 2.1 29.6

Table 3 Statistics of future reserves growth of discovered oil and gas fields in major countries of the world.

The reserves growth of discovered oil and gas fields in Russia is 23.4× 10⁹ t of equivalents, of which oil, condensate oil and natural gas reserves account for 45.6%, 3.1% and 51.3% respectively. The reserves growth of discovered oil and gas fields in Iran is 13.97× 10⁹ t, of which oil, condensate oil and natural gas reserves account for 31.3%, 8.9% and 59.8%. The reserves growth of discovered oil and gas fields in Saudi Arabia is 13.68× 10⁹ t, of which oil, condensate oil and natural gas reserves account for 75.4%, 4.7% and 19.9% respectively.

2.2.2. Distribution in different basins

The growth of global oil and gas field reserves mainly comes from the discovered oil and gas fields in 29 basins including Arabian Basin, West Siberian basin, Zagros Basin etc. The reserves growth of the Arabian Basin, Western Siberian Basin and Zagros Basin ranks the top three and the reserves growth of the three basins combined account for 42.1% of the global total (Fig. 7 and Table 4).

Fig. 7.

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	Fig. 7. Recoverable reserves growth of discovered oil and gas fields in major basins of the world.

Table 4

Table 4

Table 4 Statistics of future reserves growth of discovered oil and gas fields in major basins in the world. Basin Future reserves growth of discovered oil and gas fields/108 t Proportion of oil/% Proportion of condensate oil/% Proportion of natural gas/% Arabian 377.9 49.9 7.7 42.4 Western Siberian 154.6 48.5 2.0 49.5 Zagros 111.8 49.6 5.4 45.0 Amu Darya 66.6 0.8 1.7 97.5 Ruvuma 34.5 0 1.4 98.6 Nile Delta 33.4 60.4 4.5 35.1 Gulf of Mexico 33.2 79.0 1.4 19.6 Niger Delta 31.4 60.3 4.5 35.2 Sureste 27.8 79.4 0.1 20.5 Lower Congo 26.3 84.7 0.6 14.7

Table 4 Statistics of future reserves growth of discovered oil and gas fields in major basins in the world.

The reserves growth of discovered oil and gas fields in the Arabian Basin is 377.9× 10⁸ t, of which oil, condensate oil and natural gas account for 49.9%, 7.7% and 42.4% respectively. The reserves growth of discovered oil and gas fields in the Western Siberian Basin is 154.6× 10⁸ t, of which oil, condensate oil and natural gas take up 48.5%, 2.0% and 49.5% respectively. The reserves growth of discovered oil and gas fields in the Zagros Basin is 111.8× 10⁸ t, of which oil, condensate oil and natural gas make up 49.6%, 5.4% and 45.0% respectively.

2.2.3. Distribution onshore and offshore

The reserves growth of onshore in the global land area is 909.9× 10⁸ t, of which oil, condensate oil and natural gas make up 48.8%, 4.9% and 46.3% respectively. The reserves growth offshore is 621.8× 10⁸ t, of which oil, condensate oil and natural gas account for 45.8%, 5.1% and 49.1% respectively. The reserves growths of onshore and offshore account for 59.4% and 40.6% of the total respectively, and the land area is still the main source of reserves growth (Fig. 8).

Fig. 8.

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	Fig. 8. Histogram of distribution of future recoverable reserves growth of onshore or offshore in major basins of the world.

2.2.4. Distribution in different lithology of reservoir

The global reserves growth of discovered oil and gas fields is distributed quite evenly in carbonate and clastic reservoirs, in which the reserves growth in clastic reservoirs accounts for 53.1%, the reserves growth in carbonate reservoirs accounts for 46.6%, the reserves growth in basement and other rocks accounts for about 0.3% (Fig. 9).

Fig. 9.

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	Fig. 9. Histogram of future recoverable reserves growth of discovered oil and gas fields in different lithologic reservoirs of major basins in the world.

The global reserves growth of known clastic reservoirs is 813.4× 10⁸ t, of which oil, condensate oil and natural gas make up 53.1%, 4.7% and 42.2% respectively. It is mainly distributed in 13 basins including West Siberian Basin and Arabian Basin etc. The global reserves growth of carbonate reservoirs is 713.8× 10⁸ t, of which oil, condensate oil and natural gas occupy 51.3%, 6.1% and 42.6% respectively. It is mainly distributed in 10 basins, such as Zagros Basin and Amu Darya Basin etc.

The global undiscovered oil and gas resources are 3065.5× 10⁸ t, of which oil, condensate oil and natural gas resources are 1 302.2× 10⁸ t (accounting for 42.5%), 181.0× 10⁸ t (accounting for 5.9%) and 191.1× 10¹² m³ (accounting for 51.6%) respectively. They are mainly distributed in the Central Asia-Russia region (accounting for 26.6% of the global total), followed by the Middle East and Central and South America (accounting for 21.7% and 16.4% of the global total, respectively). The potential in Asia Pacific and Europe accounts for a low proportion.

2.3.1. Distribution in different countries

Russia has the largest potential of undiscovered resources (551.0× 10⁸ t), in which natural gas, oil and condensate oil account for 68.7%, 27.9% and 3.4% respectively. Venezuela ranks second with the potential of undiscovered resources of 327.9× 10⁸ t, in which oil, condensate oil and natural gas make up 82.2%, 1.0% and 16.8%, respectively. The United States has the potential of undiscovered resources of 266.6× 10⁸ t, in which oil, condensate oil and natural gas comprise 37.4%, 13.4% and 49.2% respectively (Fig. 10 and Table 5).

Fig. 10.

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	Fig. 10. Histogram of undiscovered oil and gas resources in major countries of the world.

Table 5

Table 5

Table 5 Statistics of undiscovered oil and gas resources in major countries of the world. Countries Undiscovered recoverable oil and gas resources/108 t Proportion of oil/% Proportion of condensate oil/% Proportion of natural gas/% Russia 551.0 27.9 3.4 68.7 Venezuela 327.9 82.2 1.0 16.8 United States 266.6 37.4 13.4 49.2 Iran 184.2 28.4 8.5 63.1 Saudi Arabia 169.1 72.8 4.7 22.5 Turkmenistan 128.2 2.8 1.1 96.1 Qatar 117.3 3.9 12.4 83.7 Canada 91.5 20.7 13.0 66.3 Nigeria 84.4 56.7 7.2 36.1 Brazil 78.0 70.9 2.8 26.3

Table 5 Statistics of undiscovered oil and gas resources in major countries of the world.

2.3.2. Distribution in different basins

The global undiscovered oil and gas resources are mainly distributed in 71 basins. The Arabia, Zagros and West Siberian basins rank the top three in terms of resource potential, and the amount of undiscovered resources in the three basins accounts for 29.4% of the global total (Fig. 11 and Table 6).

Fig. 11.

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	Fig. 11. Histogram of undiscovered oil and gas resources in major basins of the world.

Table 6

Table 6

Table 6 Statistics of undiscovered oil and gas resources in major basins of the world. Basin Undiscovered recoverable oil and gas resources/108 t Proportion of oil/% Proportion of condensate oil/% Proportion of natural gas/% Arabia 368.9 48.1 7.8 44.1 Zagros 279.8 42.5 5.8 51.7 Western Siberia 252.1 43.8 1.1 55.1 Amu Darya 167.2 0.3 2.5 97.2 Campos 149.4 86.5 0 13.5 Santos 141.7 73.2 0.8 26.0 Deepwater in the Gulf of Mexico 117.7 31.9 24.2 43.9 Eastern Siberia 107.7 5.8 5.5 88.7 East Barents Sea 90.8 8.3 4.6 87.1 Niger Delta 73.0 48.5 7.2 44.3

Table 6 Statistics of undiscovered oil and gas resources in major basins of the world.

The undiscovered oil and gas resources in the Arabian Basin are 368.9× 10⁸ t, of which oil, condensate oil and natural gas make up 48.1%, 7.8% and 44.1% respectively. The undiscovered oil and gas resources in the Zagros Basin are 279.8× 10⁸ t, of which oil, condensate and natural gas comprise 42.5%, 5.8% and 51.7% respectively. The undiscovered oil and gas resources in the West Siberian Basin are 252.1× 10⁸ t, of which oil, condensate oil and natural gas account for 43.8%, 1.1% and 55.1%.

2.3.3. Distribution onshore and offshore

The undiscovered oil and gas resources onshore are 1771.9 × 10⁸ t, of which oil, condensate oil and natural gas make up 47.8%, 5.0% and 47.2% respectively. The undiscovered oil and gas resources offshore are 1293.6× 10⁸ t, of which oil, condensate oil and natural gas comprise 45.6%, 5.1% and 49.3% respectively. The undiscovered oil and gas resources onshore and offshore account for 57.8% and 42.2% of the global total respectively (Fig. 12). The exploration potential of onshore conventional oil and gas resources is still huge, and the sea area is also an important reserve growth point in the future.

Fig. 12.

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	Fig. 12. Histogram of undiscovered oil and gas resources onshore and offshore in major basins of the world.

2.3.4. Distribution in different lithology of reservoir

The global undiscovered oil and gas resources in clastic reservoirs are slightly greater than those in carbonate reservoirs, accounting for 50.6% and 49.4% of the global total respectively. The amount of undiscovered oil and gas resources in carbonate reservoirs is 1 514.4× 10⁸ t, of which oil, condensate oil and natural gas account for 49.2%, 5.1% and 45.7% respectively. The undiscovered oil and gas resources in clastic reservoirs are 1 514.4× 10⁸ t, of which oil condensate oil and natural gas make up 53.7%, 5.7% and 40.6% respectively (Fig. 13).

Fig. 13.

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	Fig. 13. Histogram of undiscovered oil and gas resources in different lithology of major basins in the world.

3.1.1. Regional distribution of recoverable unconventional oil resources

About 73.4% of the world's recoverable unconventional oil resources are distributed in North America, Central Asia - Russia, and Central and South America. The recoverable resources in the North American region are 1 502.0× 10⁸ t, accounting for 35.7% of the world's total, and dominated by oil shale, oil sands and heavy oil; The total recoverable resources in Central Asia-Russia are 960.9× 10⁸ t, accounting for 22.8% of the world's total, and are dominated by oil shale and oil sands. The total recoverable resources in Central and South America are 627.2× 10⁸ t, accounting for 14.9% of the world's total, and are dominated by heavy oil and oil shale.

Recoverable oil shale resources are mainly distributed in North America, Central Asia - Russia and Europe; heavy oil is mainly distributed in Central and South America, North America and the Middle East; oil sands are mainly distributed in North America and Central Asia - Russia; and tight oil is mainly distributed in North America, Central Asia - Russia and Central and South America (Fig. 14 and Table 7).

Fig. 14.

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	Fig. 14. Regional distribution of recoverable unconventional oil resources in the world.

Table 7

Table 7

Table 7 Statistics on regional distribution of recoverable unconventional oil resources in the world. Region Recoverable unconventional oil resources/108 t Proportion of oil shale/% Proportion of heavy oil/% Proportion of oil sands/% Proportion of tight oil/% North America 1 502.0 46.5 21.2 26.3 6.0 Central Asia - Russia 960.9 59.4 13.7 18.9 8.0 Central-South America 627.2 23.9 65.2 0 10.9 Europe 479.5 73.8 17.2 3.7 5.3 Middle East 291.7 35.1 60.6 0 4.3 Africa 198.5 34.3 31.9 12.3 21.5 Asia Pacific 149.8 24.0 44.9 0 31.1 Total 4 209.4 47.0 29.7 14.7 8.6

Table 7 Statistics on regional distribution of recoverable unconventional oil resources in the world.

3.1.2. Regional distribution of recoverable unconventional natural gas resources

About 70.9% of the world's recoverable unconventional natural gas resources are enriched in North America, Central Asia - Russia, Asia Pacific, the Middle East. The recoverable resources in North America are 56.3× 10¹² m³, accounting for 28.8%, and are dominated by shale gas and coalbed methane. The recoverable resources in Central Asia-Russia are 36.3× 10¹² m³, accounting for 18.6%, and are dominated by shale gas and coalbed methane. The recoverable resources in the Asia-Pacific region are 24.5× 10¹² m³, accounting for 12.5%, and are dominated by shale gas and coalbed methane. The recoverable resources in the Middle East are 21.4× 10¹² m³, accounting for 11.0%, and are dominated by shale gas.

The distribution of unconventional natural gas resources in the world is relatively balanced. Except that nearly half of the recoverable resources are enriched in North America and Central Asia-Russia, the recoverable resources in other regions all make up more than 9.6%. Shale gas is distributed in every major region, with recoverable resources of above 16.0× 10¹² m³ in each region. Coalbed methane is mainly concentrated in North America, Central Asia-Russia, and the Asia Pacific region. Tight gas is largely found in the North American region and rarely distributed in other major regions (Fig. 15 and Table 8).

Fig. 15.

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	Fig. 15. Regional distribution of recoverable unconventional natural gas resources in the world.

Table 8

Table 8

Table 8 Statistics on regional distribution of recoverable unconventional natural gas resources in the world. Region Recoverable unconventional natural gas resources/1012 m3 Proportion of shale gas/% Proportion of CBM/% Proportion of tight gas/% North America 56.3 60.1 30.2 9.7 Central Asia - Russia 36.3 62.8 36.2 1.0 Central-South America 18.8 99.0 0.2 0.8 Europe 19.0 85.3 10.7 4.0 Middle East 21.4 99.0 0 1.0 Africa 19.2 99.5 0.3 0.2 Asia Pacific 24.5 74.7 24.5 0.8

Table 8 Statistics on regional distribution of recoverable unconventional natural gas resources in the world.

3.2.1. Distribution of recoverable unconventional oil resources in different countries and regions

The global unconventional oil is distributed in 55 countries. More than 80% of the recoverable resources are concentrated in the United States, Russia, Canada, Venezuela, Saudi Arabia, Brazil, Ukraine, France and Mexico etc. The recoverable unconventional oil resources in the United States are 952.5× 10⁸ t, accounting for 22.6% of the global total, and are dominated by oil shale, heavy oil and tight oil. The recoverable resources in Russia are 859.2× 10⁸ t, accounting for 20.4% of the global total, and are dominated by oil shale, oil sand and heavy oil. The recoverable resources in Canada are 405.4× 10⁸ t, accounting for 9.6% of the global total, and are dominated by oil sands. The recoverable resources in Venezuela are 307.3× 10⁸ t, accounting for 7.3% of the global total, and are dominated by heavy oil.

Oil shale is mainly distributed in the United States, Russia, Ukraine, Brazil, and France. Heavy oil is mainly distributed in Venezuela, the United States, Saudi Arabia and Mexico. Oil sands are mainly distributed in Canada and Russia. Tight oil is mainly distributed in Russia, the United States and Canada (Fig. 16 and Table 9).

Fig. 16.

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	Fig. 16. Distribution of recoverable unconventional oil resources in major countries of the world.

Table 9

Table 9

Table 9 Statistics on recoverable unconventional oil resources in major countries of the world. Countries Recoverable unconventional oil resources/108 t Proportion of oil shale/% Proportion of heavy oil/% Proportion of oil sands/% Proportion of tight oil/% United States 952.5 72.5 19.1 1.1 7.3 Russia 859.2 66.4 10.3 14.4 8.9 Canada 405.4 2.0 0 94.9 3.1 Venezuela 307.3 0 98.4 0 1.6 Saudi Arabia 230.7 24.2 73.7 0 2.1 Brazil 208.1 72.1 21.5 0 6.4 Ukraine 190.0 99.4 0 0 0.6 France 151.4 92.2 0.2 0.1 7.5 Mexico 144.1 92.2 0.2 0.1 7.5 Kazakhstan 66.3 92.2 0.2 0.1 7.5

Table 9 Statistics on recoverable unconventional oil resources in major countries of the world.

3.2.2. Distribution of recoverable unconventional natural gas resources in different countries and regions

The global unconventional natural gas is distributed in 38 countries. More than 80% of the recoverable resources are concentrated in 12 countries including the United States, Russia, Canada, Australia, Iran and Saudi Arabia. The recoverable resources in the United States are 39.5× 10¹² m³, accounting for 20.2% of the world total, where shale gas, coalbed methane and tight gas are all relatively rich. The recoverable resources in Russia are 28.5× 10¹² m³, accounting for 14.6% of the global total, and are dominated by shale gas and coalbed methane. The recoverable resources in Canada are 16.2× 10¹² m³, accounting for 8.3% of the global total, and are dominated by coalbed methane and shale gas. The recoverable resources in Australia are 14.5× 10¹² m³, accounting for 7.4% of the global total, and are dominated by shale gas and coalbed methane.

The global unconventional natural gas resources are dominated by shale gas and coalbed methane. Shale gas is mainly distributed in the United States, Russia, Australia and Iran. Coalbed methane is mainly distributed in Russia, Canada, the United States and Australia. Tight gas is mainly distributed in the United States and Canada (Fig. 17 and Table 10).

Fig. 17.

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	Fig. 17. Distribution of recoverable unconventional natural gas resources in major countries of the world.

Table 1

Table 1

Table 1 0. Statistics on recoverable unconventional natural gas resources in major countries of the world Countries Recoverable unconventional natural gas resources/1012 m3 Proportion of shale gas/% Proportion of CBM/% Proportion of tight gas/% United States 39.5 69.2 19.6 11.3 Russia 28.5 52.8 46.0 1.2 Canada 16.2 36.3 57.5 6.2 Australia 14.5 76.3 23.0 0.7 Iran 11.9 100.0 Saudi Arabia 9.0 97.6 2.4 Argentina 8.6 99.1 0.9 Algeria 8.6 100.0 Brazil 6.5 99.7 0.3 Kazakhstan 5.8 100.0

Table 1 0. Statistics on recoverable unconventional natural gas resources in major countries of the world

3.3.1. Distribution of recoverable unconventional oil resources in different basins

The global unconventional oil is mainly distributed in 134 basins. About 81.5% of the recoverable resources are distributed in 26 basins such as Alberta, Western Siberia, Volga-Ural, Piceance and Venezuela Basin. The recoverable resources in the Alberta Basin are 405.0× 10⁸ t, accounting for 9.6% of the world's total, and are dominated by oil sands and tight oils. The recoverable resources in the West Siberian Basin are 311.9× 10⁸ t, accounting for 7.4% of the world's total, and are dominated by oil shale and tight oil. The recoverable resources in the Volga-Ural Basin are 304.6× 10⁸ t, accounting for 7.2% of the world's total, and are dominated by oil shale and oil sands. The recoverable resources in the Piceance Basin are 300.6× 10⁸ t, accounting for 7.1% of the world, and are dominated by oil shale. The recoverable resources in the Eastern Venezuela Basin are 262.0× 10⁸ t, accounting for 6.2% of the world's total, and are dominated by heavy oil.

The global recoverable oil shale resources are mainly distributed in Piceance, Volga-Ural, Uinta and Western Siberian basin. The recoverable heavy oil resources are mainly distributed in eastern Venezuela, Central Arabian and West Siberian basins. The recoverable oil sand resources are mainly distributed in Alberta, East Siberia and Volga-Ural basins. The recoverable tight oil resources are mainly distributed in the West Siberia, Alberta, and Paris basins (Fig. 18 and Table 11).

Fig. 18.

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	Fig. 18. Distribution of recoverable unconventional oil resources in major basins of the world.

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Table 1 1. Statistics on recoverable unconventional oil resources in major basins of the world Basins Recoverable unconventional oil resources/108 t Proportion of oil shale/% Proportion of heavy oil/% Proportion of oil sands/% Proportion of tight oil/% Alberta 405.0 2.0 94.9 3.1 Western Siberian 311.9 65.6 10.2 24.2 Volga-Ural 304.6 86.4 13.6 Piceance 300.6 99.9 0.1 Eastern Venezuela 262.0 99.5 0.5 Uinta 228.3 98.9 1.1 Dnieper-Donets 190.0 99.4 0.6 Eastern Siberia 163.4 62.8 37.2 Central Arab 156.8 100.0 Paris Basin 145.3 96.1 3.9

Table 1 1. Statistics on recoverable unconventional oil resources in major basins of the world

3.3.2. Distribution of recoverable unconventional natural gas resources in different basins

The global recoverable unconventional natural gas resources are distributed in 106 basins. About 80% of the recoverable resources are distributed in 26 basins. The recoverable resources in the Alberta Basin are 16.2× 10¹² m³, accounting for 8.3% of the world's total, and are dominated by coalbed methane, shale gas and tight gas. The recoverable resources in the Zagros Basin are 11.9× 10¹² m³, accounting for 6.1% of the world's total, and are dominated by shale gas. The recoverable resources in the Appalachian Basin are 11.5× 10¹² m³, accounting for 5.9% of the world's total, and are dominated by shale gas and tight gas. The recoverable resources in the East Siberian Basin are 10.3 × 10¹² m³, accounting for 5.3% of the world's total, and are dominated by shale gas and coalbed methane. The recoverable resources in the US Gulf Basin are 9.8 × 10¹² m³, accounting for 5.0% of the world's total, and are dominated by shale gas.

Global shale gas is mainly distributed in the Zagros, US Gulf Coast, Appalachian, and Ghadames basins. CBM is mainly distributed in Alberta, East Siberia, and Kuznetsk basins. Tight gas is mainly distributed in Alberta and Appalachian basins (Fig. 19 and Table 12).

Fig. 19.

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	Fig. 19. Distribution of recoverable unconventional natural gas resources in major basins of the world.

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Table 1 2. Statistics on recoverable unconventional natural gas resources in major basins of the world. Basin Recoverable unconventional natural gas resources/1012 m3 Proportion of shale gas/% Propor- tion of CBM/% Proportion of tight gas/% Alberta 16.2 36.3 57.5 6.2 Zagros 11.9 100.0 Appalachia 11.5 78.5 8.1 13.4 Eastern Siberia 10.3 55.2 44.8 US Gulf Coast 9.8 94.5 1.1 4.4 Central Arab 8.9 98.0 2.0 Ghadames 8.6 100.0 Kuznetsk 8.5 100.0 Canning 6.5 100.0 Parana 6.5 99.7 0.3

Table 1 2. Statistics on recoverable unconventional natural gas resources in major basins of the world.