A Study on the Applicability of Aromatic Parameters in the Maturity Evaluation of Lacustrine Source Rocks and Oils Based on Pyrolysis Simulation Experiments

Abstract

Aromatic maturity parameters were evaluated via closedsystem pyrolysis experiments using a Mesozoic lacustrine source rock from the Yingen-Ejinaqi Basin, thereby ensuring a uniform source. Pulverized rock aliquots (200 mg) were reacted with water at temperatures ranging from 250 to 550 °C at 5 °C/min, and the aromatic fractions of expelled oil and extracts of the solid residue were analyzed by GC−MS. The experiments showed that the relative abundance of aromatic hydrocarbons in the oil and extractable organic matter (EOM) of source rock had different evolutionary characteristics. With the increase in the thermal evolution degree, the relative abundance of aromatic hydrocarbons in the EOM showed the characteristics of ″increased early (R o < 0.80), unchanged middle (R o = 0.80−2.00%), decreased lately (R o > 2.00%)″. While the relative abundance of aromatic hydrocarbons in the expelled oils continuously increased, as the R o values increased from 0.62 to 2.39%, the relative abundance of aromatic hydrocarbons gradually increased from 8 to 46%. With increased maturity, the relative abundance of 1−3-ring aromatic hydrocarbons continuously decreased, as observed in the phenanthrene homologs. Meanwhile, the relative abundance of 4+-ring aromatic hydrocarbons continuously increased, as seen in chrysene homologs. It was suggested that the effects of maturity on the composition of aromatic hydrocarbons might not be sufficiently obvious. The effective application range of the alkylnaphthalenerelated maturity parameters (2-/1-methylnaphthalenes,