Abstract
The methylphenanthrene distributions of crude oils from oil and gas fields have been measured in the JAPEX Research Center as a part of the routine geochemical analysis since 2004. We have examined the validity of the two methylphenanthrene maturity parameters, the methylphenanthrene index 1 (MPI 1) and the methylphenanthrene ratio (MPR), for crude oils in Niigata Prefecture (the Niigata oils). The results are summarized as follows.
1) The Niigata oils show a regular change with maturity on the MPI 1-MPR plot.
2) The Niigata oils are divided into the following three maturation stages on the MPI 1-MPR plot.
Stage 1 : oil generation stage
Stage 2 : condensate generation stage
Stage 3 : oil cracking stage
3) The MPI 1-MPR plot is applicable to crude oils in the Akita and Hokkaido districts.
4) This plot is useful for the estimation of relative maturity levels and the oil to oil correlation.
