Investigating Source, Age, Maturity, and Alteration Characteristics of Oil Reservoirs Using APGC/MS/MS Analysis of Petroleum Biomarkers

Significance of the Topic

Petroleum biomarkers represent molecular fossils preserved under geological conditions, acting as the DNA of crude oils. They reveal the biological source, depositional environment, and thermal history of organic matter, enabling reliable oil fingerprinting and correlation with source rocks. This knowledge is critical for exploration, reservoir characterization, and economic evaluation in upstream applications.

Objectives and Scope

The study introduces Atmospheric Pressure Gas Chromatography coupled with tandem quadrupole mass spectrometry (APGC-MS/MS) as a robust approach for analyzing sterane and hopane biomarkers in crude oils and source rocks. Goals include enhancing sensitivity and selectivity, comparing APGC with traditional electron ionization methods, and demonstrating unambiguous detection of low-abundance biomarkers to determine oil source, age, maturity, and alteration.

Methodology and Used Instrumentation

Samples were prepared by precipitating asphaltenes with n-heptane and separating saturate fractions. Instrumentation and parameters included

• Gas chromatograph: Agilent 7890 with 7683B autosampler and Restek Rxi-5Sil MS column (30 m × 0.25 mm, 0.25 µm); helium carrier at 1 mL/min; temperature ramp from 50 °C to 315 °C.
• APGC source on Waters Xevo TQ-S: corona current 2 µA, source temp 150 °C, nitrogen cone and auxiliary gas flows, producing soft ionization.
• Mass spectrometry: multiple reaction monitoring with optimized precursor→product transitions for C26–C35 steranes and hopanes.

Main Results and Discussion

APGC generates intense molecular radical cations with minimal fragmentation, in contrast to extensive fragmentation in EI. This enhances precursor ion abundance for MRM transitions and lowers detection limits. Case studies include

• Jurassic North Sea oil: APGC-MS/MS confirmed marine origin via C30 sterane detection, determined C28/C29 sterane ratio (0.41) and 24-nordiacholestane ratio (0.20) to constrain source age.
• Côte d’Ivoire mixed-input oil: traditional GC-MS SIR suggested terrestrial input, but APGC-MS/MS revealed the marine C30 sterane contribution, refining depositional history.
• Oleanane vs lupane differentiation: APGC-MS/MS distinguished oleanane by monitoring the m/z 412→369 transition to confirm absence of lupane.

Benefits and Practical Applications

Key advantages of APGC-MS/MS for petroleum biomarker analysis include

• Soft ionization yielding abundant molecular ions and improved MRM selectivity.
• Enhanced sensitivity for trace biomarkers without extensive sample cleanup.
• Compatibility with existing GC-MS/MS MRM transitions for seamless data integration.
• Accurate determination of oil origin, maturity, and alteration for exploration decisions.

Future Trends and Potential Applications

Emerging directions involve

• Integration of APGC with UPLC or UPC² for expanded compound coverage.
• Application to novel biomarker classes and isomeric differentiation.
• High-throughput workflows and automation in geochemical laboratories.
• Machine learning algorithms for pattern recognition and reservoir characterization.

Conclusion

APGC-MS/MS on a single quadrupole platform offers a powerful, sensitive, and selective method for petroleum biomarker analysis. By delivering strong molecular ions and utilizing tailored MRM transitions, it advances the accuracy of oil source, age, and depositional environment determinations, supporting robust geochemical interpretations and exploration strategies.

References

1. Holba AG, Dzou LIP, Masterson WD, et al. Application of 24-norcholestanes for constraining source age of petroleum. Org Geochem. 1998;29(5–7):1269–1284.
2. Nytoft HP, Jørgensen A, Koefoed B, Christiansen FG, Fowler MG. Oleanane or lupane? Reappraisal of the presence of oleanane in Cretaceous–Tertiary oils and sediments. Org Geochem. 2002;33:1225–1240.
3. Peters KE, Walters CC, Moldowan JM. The Biomarker Guide. Cambridge University Press; 2005.