Unravelling maturity- and migration-related carbazole and phenol distributions in Central Graben crude oils

Oil maturity could be assessed using established changes in carbazole annelation (N1 DBE 9 vs. 12 vs. 15 classes), as well as hydrocarbon biomarkers. 29Ts/(29Ts + NH) correlated best with the polar compound maturity data. Secondary migration fractionation appears nevertheless to have played a role, as seen by increased DBE 9 and 12 carbazole and benzocarbazole proportions and a loss of C2-3 DBE 12 homologues within carbonate reservoirs as compared to intraformational Upper Jurassic siliciclastic reservoirs. Thus migration distances, pathways and wettability of carrier systems ostensibly play a significant role in carbazole distributions of the Central Graben oils, manifesting itself as apparent maturity retardation. In an attempt to eliminate the migration component from maturity assessment, we here present a novel ternary diagram including dibenzocarbazoles (N1 DBE 15) and phenolic species (O1 DBE 4 and 5) based on a single measurement using the FT-ICR-MS. However, the integration of such results into 3D-modelling software must be conducted to clarify source kitchen, migration pathways and distances.