NATURAL OCCURRENCE OF TETRAMANTANE (C22H28) PENTAMANTANE (C26H32) AND HEXAMANTANE (C30H36) IN A DEEP PETROLEUM RESERVOIR

A suite of petroleum polymantanes, including tetramantane, pentamantane and hexamantane, was discovered in a gas condensate produced from a very deep (similar to 6800 m below the surface) petroleum reservoir located in the US Gulf Coast. This appears to be the first reported natural occurrence of these compounds. Three isomers of tetramantane, four isomers of pentamantane and a number of their alkylated compounds were identified using full-scan GC/MS analysis. Results from selective ion monitoring GC/MS analysis suggest the presence of hexamantane. The polymantanes are associated with abundant lower adamantologues, including adamantane, diamantane (congressane), triamantane and their alkyl-substituted compounds. The genesis of polymantanes in petroleum is not known. It is speculated that they may have been formed via homologation of the lower adamantologues at high pressure and temperature in the reservoir. The lower adamantologues are believed to have been formed originally by the catalytic rearrangement of tricycloalkanes during or after oil generation.