Variation in abundance and distribution of diamondoids during oil cracking

In this study, changes in the abundance and distribution of diamondoids in petroleum with thermal maturity were investigated by a simulation oil cracking experiment. Highly sensitive and selective gas chromatography–triple quadrupole mass spectrometry (GC–MS–MS) was employed to quantify diamondoids at ppm and sub-ppm levels. The results indicate that diamondoids were generated primarily within the maturity range 1.0–2.1% EasyRo and destroyed at high thermal maturity (>2.1% EasyRo). Hence, the occurrence of high concentrations of diamondoids probably corresponds to the maturity range from the wet gas to the early dry gas stage (i.e., 1.5–2.5% EasyRo). Good correlations were observed between a few ratios of diamondoids (i.e., EAI, DMAI-1, DMDI-1 and TMAI-1) and EasyRo. This finding indicates that these parameters may be useful maturity indices for organic matter from the late oil window to the dry gas window.