Natural occurrence of higher thiadiamondoids and diamondoidthiols in a deep petroleum reservoir in the Mobile Bay gas field

Abstract

A series of higher thiadiamondoids and diamondoidthiols, including thiatetramantanes, tetramantanethiols, thiapentamantanes, pentamantanethiols, thiahexamantanes, hexamantanethiols and thiacylcohexamantane, was discovered in a gas condensate produced from a very deep (6274 m, 20,585 ft) petroleum reservoir in the Bon Secour Bay in the Mobile Bay gas field, located offshore Alabama in the northern Gulf of Mexico, USA. This appears to be the first reported natural occurrence of these compounds. Several isomers of higher thiadiamondoids and diamondoidthiols were identified using full scan gas chromatography–mass spectrometry (GC–MS) coupled with GC–sulfur chemiluminescence detection (GC–SCD) and GC × GC-time of flight mass spectrometry (GC × GC–TOFMS). These higher thiadiamondoids and diamondoidthiols are associated with abundant lower homologs including thiaadamantanes, thiadiamantanes, thiatriamantanes and their thiol groups. The origin of these compounds in petroleum has not been reported. It is speculated that similar to lower thiadiamondoids and diamondoidthiols, higher ones are possibly formed from the sulfurization of their precursor diamondoids during TSR, a conclusion supported by the occurrence of open-cage higher diamondoidthiols and sulfur isotopic data of higher thiadiamondoids and diamondoidthiols isolated from the Mobile Bay condensate. The presence of higher thiadiamondoids and diamondoidthiols is indicative of the occurrence of TSR and can be used to predict sour gas production.