Middle East Economic Survey
VOL. XLIX
No 12
GENERAL
Global Natural Gas Reserves � A Heuristic Viewpoint (Part 2 Of 2)
By Rafael Sandrea,
The following article was written for MEES. Rafael Sandrea is President and CEO of ITS Servicios Tecnicos, a Caracas-based engineering company he founded 30 years ago. He holds a PhD in petroleum engineering from Penn State University and has written more than 30 technical publications, including the book, Dynamics of Petroleum Reservoirs under Gas Injection, Gulf Publishing, 1974. (rafael@its.com.ve). Part 1 was published in last week痴 MEES.
Part 2 � Discusses a heuristic approach, based on an assumed analogy between giant oil and gas fields, to obtain an approximation for global ultimate recoverable gas reserves. The basis of the analogy stems from the premise that oil and conventional natural gas are produced by the same geologic process and are often found together in the most important hydrocarbon rich provinces.
Many of the largest gas fields in the world have not yet been brought on stream or are in the start-up mode. For example, the world痴 largest gas field, North Dome (North Field/South Pars), is only producing 10% of its planned full-scale production of 45bn cfd. Production from other giant fields like Prudhoe Bay and several Russian and Middle Eastern fields is on hold pending the construction of pipeline systems and customers.
Giant oil fields are the core of the oil industry because they provide a significant share of the world痴 supply. The world痴 120 largest oilfields � 3% of the 4,000 total active oilfields � produce almost half of the world痴 production1. For this comparative analysis, the world痴 15 top oil and 15 top non-associated gasfields were selected. Table 1 lists these 30 special giant fields specifying their size and year of discovery. The size of the gas fields is also expressed in volumes of equivalent oil so as to make easy their comparison with the oil counterparts. Eight of the 15 giant gasfields are located in Russia and contain 30% of the total reserves of the group. Two fields in the Middle East together account for 55% of the group痴 reserves. Figure 1 illustrates graphically the size distribution of each set of oil and gas fields.
Before analyzing the size distributions, it should be pointed out that in contrast to the giant oilfields for which estimates of their recoverable reserves are well established, this is not the case with the gas giants. Eight (identified with an asterisk in Table 1) of the 15 top gasfields have only volumetric estimates of their reserves either because they have yet to go on production or have very little production history as is the case of the North Dome and Zapolyarnoye fields. Both circumstances preclude the options of decline curve analysis or dynamic reservoir modeling technique to determine reserves. The eight gasfields with volumetric estimates have all been properly audited and committed to large-scale developmental investments, indicative of a high level of confidence in the estimate of their reserves. Nonetheless, volumetric estimates generally have a tendency to be on the high side. This departure in the discussion was considered essential since the eight fields in question represent 70% of the reserves of the entire group of 15.
Two observations are pertinent about the size distributions. The biggest gasfield, North Dome, is almost three times the size of Ghawar, the world痴 largest oilfield. In contrast, the remaining 14 gasfields tend to be significantly smaller � roughly one-third less in size � than their 14 oil counterparts. Taken all together, both groups of 15 fields contain similar volumes of reserves: 369bn barrels for the oilfields and 433bn boe for the gasfields. This difference of roughly 15% is not considered significant in view of the fact that the majority of the gasfields have only volumetric estimates of their reserves versus more reliable estimates for the oilfields. Additionally, the volumetric gas reserves values are further converted to their thermal equivalence of oil.
The general conclusion would be that, in the best-case scenario, there appears to be as much ultimate recoverable reserves of non-associated gas as there are of crude oil. Based on a median value of 2,000bn barrels from published2 estimates of the ultimate reserves of oil, the corresponding value for non-associated gas would be roughly 12,000 trillion cu ft. To this value, estimates of associated natural gas reserves would have to be added. These are approximately 1,500 trillion cu ft based on an average solution gas-oil ratio of 750 cu ft/barrel for the 2,000bn barrel reserves of crude. The total best-case estimate of global ultimate recoverable gas reserves would then be 13,500 trillion cu ft.
Conversely, if the outsize North Dome field is considered an anomaly and the comparison is made of the size distributions of the remaining 14 fields in each group, the estimate of non-associated gas reserves would be one-third less than the previous case, or 8,000 trillion cu ft. After adding the associated gas reserves of 1,500 trillion cu ft, total reserves of associated and non-associated gas in this alternate scenario would stand at 9,500 trillion cu ft. Finally, global ultimate recoverable gas reserves should then fall in a range between 9,500 and 13,500 trillion cu ft.
The USGS recently published3 its assessment of world resources of conventional natural gas. Using geoscientific analyses they established values in a range from 10,200 to 15,400 trillion cu ft. The higher limit includes estimates (5,200 trillion cu ft) of yet-to-find reserves. The propinquity of the results from two radically different heuristic approaches is reassuring.
The Impact Of LNG And GTL Technologies On Reserves
Undoubtedly LNG facilities are vital to the worldwide monetization of natural gas. A typical 1bn cfd project requires a massive 15 trillion cu ft of proven reserves over 30 years4. A huge 35% of the wellhead gas is lost creating, transporting and re-gasifying the LNG. Likewise, emerging gas-to-liquids (GTL) plants to produce synthetic fuel products, mostly diesel and naphtha, also require major reserves5. The thermal efficiency of current GTL processes is about 60%, implying a requirement of 10mn cu ft of dry gas for each barrel of diesel produced. A 50,000 b/d plant would therefore require 5 trillion cu ft of reserves over 20 years, approximately the time needed to amortize the large investments. The relatively low efficiencies of these processes will evidently have to be factored into the ultimate recoverable gas reserves, at both the field and country levels. This is perhaps one of the reasons why Qatar has slowed or delayed some of the GTL projects into the next decade.
Highlights
A heuristic approach was taken to obtain a second approximation of worldwide gas reserves based on a comparative analogy of the size distributions of giant oil and giant non-associated gasfields. The results indicate that in a best-case scenario the ultimate recoverable reserves of conventional natural gas may be similar to those of crude oil. Global reserves were estimated to range between 9,500 and 13,500 trillion cu ft. The comparable range of values assessed by the USGS varies from 10,200 to 15,400 trillion cu ft.
Gas exporting countries are in a headlong rush to install LNG facilities and, to a lesser extent, build emerging GTL plants to produce synthetic fuel products. These projects require major capital investments and enormous reserves. The efficiencies of these technologies range about 60-65%, which implies that losses of wellhead gas and hence reserves are high, roughly one-third.
The world is also known to have substantial unconventional natural gas resources6 that have received very little attention. After US gas production from traditional oil and gas fields maxed at 22 trillion cu ft/year in 1973, output from unconventional sources � CBM and shale gas � has grown significantly over the last 20 years. Together they now account for 11% of US dry gas production. Present estimates of likely recoverable reserves of US CBM and shale gas resources are 60 trillion cu ft and 55 trillion cu ft, respectively. Boosting these reserves is the next challenge.
CBM development is now widespread around the globe but shale gas activity is very low. Worldwide, likely recoverable resources of CBM are estimated to be 550 trillion cu ft, and of shale gas it is roughly 250 trillion cu ft. At the more speculative end are methane hydrates with worldwide estimates of 3,000 trillion cu ft of in-place resource apt to be developed in the near term.
Notes:
1. The World痴 Giant Oil Fields, Matthew R Simmons, Hubbert Center Newsletter No 2002/1 January 2002.
2. Oil Prophets: Looking at World Oil Studies over Time, Steve Andrews and Randy Udall, ASPO Conference, 26-27 May 2003, Paris.
3. Global Perspectives on Petroleum Resources, Thomas Ahlbrandt, USGS World Energy Project Chief, 3rd Joint OPEC/IEA Workshop, 15 May 2005.
4. Matthew Simmons in interview for glogalpublicmedia.com, 19 May 2004.
5. 鉄tranded Gas, Diesel Needs Push GTL Work�, I I Rahmim, Oil and Gas Journal, 14 March 2005.
6. 填nconventional Gas Resources Fill the Gap in Future Supplies�, Perry A Fischer, Editor, World Oil, August, 2004.
Table 1
World痴 15 Largest Oil And Gas Fields
Oil Fields |
|
Gas Fields |
||||||
Field |
Discovery |
Size |
|
Field |
Discovery |
Size |
||
Country |
Year |
Bn Barrels |
|
Country |
Year |
Trillion Cu Ft |
Bn BOE |
|
Ghawar |
1948 |
80 |
|
North Field-S Pars |
1976 |
1,400* |
233 |
|
Saudi Arabia |
|
|
|
Qatar-Iran |
|
|
|
|
Burgan |
1938 |
60 |
|
Urengoy |
1966 |
222 |
37 |
|
Kuwait |
|
|
|
Russia |
|
|
|
|
Bol咩ar Coastal |
1917 |
32 |
|
Yamburg |
1969 |
138 |
23 |
|
Venezuela |
|
|
|
Russia |
|
|
|
|
Sufaniya |
1951 |
30 |
|
Hassi R樽el |
1956 |
123 |
20 |
|
Saudi Arabia |
|
|
|
Algeria |
|
|
|
|
R伹iala |
1953 |
20 |
|
Shtokman |
1989 |
110* |
18 |
|
Iraq |
|
|
|
Russia |
|
|
|
|
|
|
|
|
|
|
|
|
|
Ahwaz |
1958 |
17 |
|
Zapolyarnoye |
1965 |
95* |
16 |
|
Iran |
|
|
|
Russia |
|
|
|
|
Marun |
1964 |
16 |
|
Hugoton |
1926 |
81 |
13 |
|
Iran |
|
|
|
USA |
|
|
|
|
Kirkuk |
1927 |
16 |
|
Groningen |
1959 |
73 |
12 |
|
Iraq |
|
|
|
Netherlands |
|
|
|
|
Romashkino |
1948 |
16 |
|
Bonavenko |
1971 |
70* |
12 |
|
Russia |
|
|
|
Russia |
|
|
|
|
Tengiz |
1979 |
15 |
|
Medvezhye |
1967 |
68 |
11 |
|
Kazakhstan |
|
|
|
Russia |
|
|
|
|
|
|
|
|
|
|
|
|
|
Gachsaran |
1928 |
15 |
|
North Pars |
1973 |
48* |
8 |
|
Iraq |
|
|
|
Iran |
|
|
|
|
Aghajari |
1938 |
14 |
|
Dauletabad-Donmez |
1974 |
47* |
8 |
|
Russia |
|
|
|
Turkmenistan |
|
|
|
|
Samotlor |
1966 |
14 |
|
Karachaganak |
1979 |
46* |
8 |
|
Russia |
|
|
|
Kazakhstan |
|
|
|
|
Zakum |
1964 |
12 |
|
Orenburg |
1966 |
45 |
7 |
|
Abu Dhabi |
|
|
|
Russia |
|
|
|
|
Abqaiq |
1964 |
12 |
|
Kharsavey |
1974 |
42* |
7 |
|
Saudi Arabia |
|
|
|
Russia |
|
|
|
|
Top 15 369 |
Top 15 2,608 433 |
|||||||
World 2,000 |
World 9,500 � 13,500 |
|||||||
|
|
|
|
|
|
|
|
|
Notes: Gasfields are non-associated gas and gas condensate. Size refers to ultimate recoverable reserves expressed in trillion cu ft and trillion boe. Asterisk (*) indicates the reserves estimate is volumetric.
Sources: 哲atural Gas�, E N Tiratsoo, Gulf Publishing Co, 1979; Gibson Consulting Oil Statistics; EIA Reports; IIASA 2004; Author痴 decline estimates.