Differences in geochemistry and hydrocarbon generation of source-rock samples dominated by telalginite and lamalginite: A case study on the Permian saline lacustrine source rocks in the Jimusaer Sag, NW China

The Middle Permian Lucaogou Formation in Northwestern China mainly contains typical saline lacustrine oil shale. To study the differences in geochemistry and hydrocarbon generation of source-rock samples in Lucaogou Formation in Jimusaer Sag, 57 core samples from two boreholes were analyzed herein by performing total organic carbon (TOC) analysis, Rock–Eval pyrolysis, and gas chromatographic–mass spectrometry experiments on saturated hydrocarbons. The kinetics of oil generation were studied using two samples comprising typical maceral components. The results showed that the hydrocarbons produced by telalginite are relatively rich in pristane (Pr), phytane (Ph), β-carotane, high-carbon normal alkanes, and C₂₉ regular steranes. Hydrocarbons produced by lamalginite contain a significantly higher content of C₂₀ tricyclic terpanes (TT), C₂₁TT, C₂₄ tetracyclic terpanes (TeT), C₂₉ norhopane, and C₂₈ regular sterane. Based on the pyrolysis and biomarker compound parameters, telalginite has a higher conversion rate for hydrocarbons than lamalginite in the low-mature to mature stage, which is consistent with their kinetic analysis. Lamalginite source rock displays a much narrower distribution of activation energies than telalginite source rocks. Such narrower activation energy distribution effectively narrows the main stage of hydrocarbon generation. In addition, the activation energy distribution of lamalginite concentrated in the high-value interval, indicating the characteristics of the relatively lagging hydrocarbon generation of lamalginite.