egm notes, page-17

stockers old chap,
the conversion from petajoules to tcf's depends on the gas composition, namely if it contains ethane butane propane etc in addition to methane. the heavier gases add to the heat rating. this is one reason why the CBM guys (pure methane) have a bit of an issue selling into existing markets and may have to spike their product, or take an adjusted price. of course any inerts decrease the rating. at the moment it is not worth the effort to go far beyond the very convenient 1 for 1 as indicative.

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