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.



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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. Com- mon 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. 1

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TABLE D.1 Comparison of Methane Measurements 10 By Volume, By Weight, TCF m3 Pg Conventional natural gas (Methane)a Global assessment of conventional methane in reserves and 16,000 4.4 × 1014 3.2 × 102 APPENDIX D technically recoverable resources 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, ~35,000,000 ~1018 ~7.1 × 105 of the methane content of gas hydrate Recent range of global estimates of methane in methane hydrate 35,000 to 1 × 1015 to 7.1 × 102 to 177,000 5 × 1015 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 85.4 1.7 2.4 × 1012 methane from hydrate on the North Slope of Alaska Estimate of methane in hydrate, eastern Nankai Trough, Japan 40 1.14 × 1012 8.1 × 10–1 Atmospheric methanec Atmospheric abundance of methane ~250 ~5 ~7 × 1012 Estimate of total global flux of methane from all sources entering the 30 0.6 8.4 × 1011 atmosphere per year Estimate of total global sink for all methane entering the atmosphere 29 0.58 8.1 × 1011 per year a See Chapter 1. b See Chapter 2. c For discussion, see Kvenvolden, K. A. and B. W. Rogers. 2005. Gaia’s breath—global methane exhalations. Marine and Petroleum Geology 22:579-590.