Method for increasing methane recovery from a subterranean coal formation by injection of tail gas from a hydrocarbon synthesis process

A method for increasing the production of methane from a subterranean coal formation penetrated by at least one injection well and at least one production well, the method comprising:

• producing methane from the coal formation through at least one production well;
• passing at least a portion of the methane to a synthesis gas generation zone wherein at least a major portion of the methane is reacted with an oxygen containing gas to produce a mixture of carbon monoxide and hydrogen;
• passing the mixture to a hydrocarbon synthesis zone wherein at least a major portion of the carbon monoxide and hydrogen are reacted to produce a heavier mixture of hydrocarbons containing more than one carbon atom per molecule and a tail gas comprising nitrogen and carbon dioxide;
• separating at least a major portion of the tail gas from at least a major portion of the hydrocarbons and recovering the hydrocarbons as a product stream;
• compressing at least a portion of the tail gas to a pressure suitable for injection into the coal formation;
• and
• injecting at least a portion of the tail gas into the coal formation through at least one injection well.