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Realize the Energy Potential of Methane Hydrate for the United States
APPENDIX D
Comparison of Units of Measurement of Amounts of Methane by Volume and Weight
Amounts of methane can be reported either by volume or by weight. In the petroleum industry, amounts are given by volume, commonly as trillions (1012) of cubic feet (ft3) or TCF and billions (109) of ft3 (BCF) in the United States. Elsewhere in the world, where the metric system is used, the amounts are usually reported in cubic meters (m3). A convenient conversion factor is 35.3 ft3/m3.
In the oceanographic and atmospheric communities, amounts of methane are often reported by weight, that is, grams (g) or metric tons (106 g) usually with an appropriate prefix to simplify the use of exponents. Common expressions are teragrams (Tg = 1012 g), petagrams (Pg = 1015 g), and gigatons (Gt = 109 × 106 or 1015). The conversions from volume to weight or from weight to volume of methane are based on the relationship that a mol of methane, weighing 16 g, has a volume of 22.4 liters at standard temperature and pressure (STP). Useful conversion factors are 714 g/m3 and 20.2 g/ft3.
The following table compares amounts of methane in units of TCF, m3, and Pg in three categories: (1) assessments of amounts of conventional natural gas (methane); (2) estimates of the amounts of methane in methane hydrate; and (3) amounts of methane in the atmosphere.
OCR for page 160
Realize the Energy Potential of Methane Hydrate for the United States
TABLE D.1 Comparison of Methane Measurements
TCF
By Volume, m3
By Weight, Pg
Conventional natural gas (Methane)a
Global assessment of conventional methane in reserves and technically recoverable resources
16,000
4.4 × 1014
3.2 × 102
U. S. methane consumption in 2008
23
6.5 × 1011
4.7 × 10−1
Methane in methane hydrateb
Very early global estimates, based on many erroneous assumptions, of the methane content of gas hydrate
~35,000,000
~1018
~7.1 × 105
Recent range of global estimates of methane in methane hydrate
35,000 to 177,000
1 × 1015 to 5 × 1015
7.1 × 102 to 3.6 × 103
Mean MMS estimate of methane in hydrate in the Gulf of Mexico
21,000
6 × 1014
4.3 × 102
Mean U. S. Geological Survey estimate of technically recoverable methane from hydrate on the North Slope of Alaska
85.4
2.4 × 1012
1.7
Estimate of methane in hydrate, eastern Nankai Trough, Japan
40
1.14 × 1012
8.1 × 10−1
Atmospheric methanec
Atmospheric abundance of methane
~250
~7 × 1012
~5
Estimate of total global flux of methane from all sources entering the atmosphere per year
30
8.4 × 1011
0.6
Estimate of total global sink for all methane entering the atmosphere per year
29
8.1 × 1011
0.58
aSee Chapter 1.
bSee Chapter 2.
cFor discussion, see Kvenvolden, K. A. and B. W. Rogers. 2005. Gaia’s breath—global methane exhalations. Marine and Petroleum Geology 22: 579- 590.