Methylphenanthrene maturity index of marine source rock extracts and crude oils from the Maracaibo Basin

Abstract Phenanthrenes in marine source rock extracts (La Luna Formation) and marine crude oils with increasing level of maturity were examined by GC-MS. For low and medium maturity ranges, MPI values of rock extracts do not vary significantly with increasing maturity and do not correlate with T max or atomic H/C ratio values of rocks and kerogens respectively. Anomalous MPI values found are attributed to lithologic changes. In the crude oils analyzed, MPI values do not correlate with selected biological marker maturity parameters. For very mature rock extracts and crude oils (as assessed by elemental analysis) MPI reaches very high values. At this level of maturity MPI index seems to be useful for the assessment of thermal maturity. The tricyclic terpane ratios (C 23 /C 21 and C 23 /C 24 ) have been found particularly useful in the assessment of thermal maturation of the La Luna source rock extracts and the La Luna derived crude oils.