Trimethyldibenzothiophenes: Molecular tracers for filling pathways in oil reservoir

- Two indicators relative to TMDBTs were used in tracing oil filling pathways.
- TMDBT parameters were confirmed potential tracing indicators based on the thermal stability and molecular simulation.
- Oil filling pathways in both Ordovician carbonate reservoir and Eocene sandstone reservoirs are investigated.

Based on the thermodynamic stabilities and molecular simulation, two trimethyldibenzothiophene molecular indicators, that is, 2,4,6-/(1,4,6 + 1,4,8 + 3,4,6)-trimethyldibenzothiophene (TMDBT) and (2,4,7 + 2,4,8)-/(1,4,6 + 1,4,8 + 3,4,6)-TMDBT (the numbers indicate the position of methyl-substitute), were proposed to trace subsurface oil migration orientations and reservoir filling pathways. In this paper, we successfully applied the aforesaid parameters both in an Ordovician carbonate reservoir of the Tuoputai region of the Tarim Basin (NW China), and in an Eocene clastic lacustrine reservoir of the Fushan Depression in the Beibuwan Basin, South China Sea. Besides the migration fractionation is proven the main control factor for the relative contents of TMDBT isomers in corresponding oils, which indicates that the trimethyldibenzothiophene molecular parameters can serve as the effective oil migration tracer in an oil reservoir, especially in high to over mature and severely biodegraded oils.