A highly sensitive and accurate multiplex gas chromatography–mass spectrometry–mass spectrometry (GC/MS/MS) technique and GC/MS technique are tested for terpanes in a hydrocarbon source rock sample. The terpanes, including tricyclic, tetracyclic, and pentacyclic, were quantified monitoring and identified with the transition m/z (262+14n)→191, 330→191, and (370+14n)→191 by multiple reaction monitoring of GC/MS/MS technique using collision energies of 5–30 eV. Results show that collision energies have great influence on tricyclic and pentacyclic terpanes' ratios. After comparing the analysis results by GC/MS, the collision energy for detecting terpanes using the MRM-MS/MS method is optimized at 23 eV.

Rock-Eval pyrolysis and the biomarker composition of organic matter were systematically studied in hydrate-bearing sediments from the Shenhu area, South China Sea. The n-alkane distribution patterns revealed that the organic matter in the sediments appeared to originate from mixed sources of marine autochthonous input, terrestrial higher plants, and ancient reworked organic matter. The low total organic carbon contents (average < 0.5%) and the low hydrogen index (HI, <80 mg HC/g TOC) suggested the poor hydrocarbon-generation potential of the deposited organic matter at a surrounding temperature of <20 °C in unconsolidated sediments. The abnormally high production index and the fossil-originated unresolved complex mixture (UCM) accompanied by sterane and hopane of high maturity indicated the contribution of deep hydrocarbon reservoirs. Preliminary oil-to-source correlation for the extracts implied that the allochthonous hydrocarbons in the W01B and W02B sediments might have originated from the terrestrial source rocks of mature Enping and Wenchang formations, while those of W03B seem to be derived from more reduced and immature marine source rocks such as the Zhuhai formation. The results of the organic extracts supported the previous identification of source rocks based on the isotopic composition of C₂₊ hydrate-bound gases. The biomarker of methanogens, squalane, was recognized in the sediments of this study, possibly suggesting the generation of secondary microbial gases which are coupled with the biodegradation of the deep allochthonous hydrocarbons.

The Lucaogou Formation in the Santanghu Basin is notable for its abundance of oxygen-containing compounds, especially the γ-alkylbutyrolactone series (GBLs), which were detected for the first time in the shales. However, the origin and geological significance of these compounds in sediment are unclear. In this study, source rock samples from the Lucaogou Formation in the Santanghu Basin were collected and classified into two categories (high-GBL content (Group H); low-GBL content (Group L)) based on gas chromatography–mass spectrometry. The biomarker results indicate that the medium-chain n-alkanes in Group H are more enriched. In addition, the source rocks of both Group H and Group L were formed in a reducing and salinized sedimentary environment. The Rock-Eval pyrolysis results indicate that Group H has high organic matter abundance and organic matter types of I–II₁, illustrating the contribution of submerged algae, whereas Group L has low organic matter abundance and organic matter types II₂–III. Based on the above results, the GBLs exhibit typical biogenic characteristics and is likely to originate from specific submerged algae. Thermal simulation experiments further confirm that Group H has a greater hydrocarbon generation. Combined with gas isotope evidence, these findings show that the high abundance of GBLs compounds is effectively preserved during the formation of excellent source rocks and promotes the formation of petroleum.