Petroleum type determination through homogenization temperature and vapour volume fraction measurements in fluid inclusions

Physical parameters of petroleum‐bearing fluid inclusions such as bulk density (ρ), molar volume (V_m), vapour volume fraction (?_vap) and homogenization temperature (T_h) are essential information to model petroleum composition (x) in inclusions and to reconstruct palaeotemperature and palaeopressure of trapping. For the main petroleum types contained in a fluid inclusion, we can follow how ?_vap and T_h are simultaneously influenced by a change of bulk density in a ?_vap versus T_h projection. We have correlated T_h and ?_vap for different petroleum compositions for a large range of bulk density values. However, postentrapment events under new pressure (P) and temperature (T) conditions can greatly modify the initial fingerprints of physical conditions and chemical composition of fluid inclusions. Re‐equilibration is frequent, especially in the case of fragile minerals. Stretching and leakage phenomenon have been simulated using the Petroleum Inclusion Thermodynamics (pit ) software, from virtual petroleum inclusions with known hydrocarbon composition. The aim of these simulations is to understand how ?_vap and T_h evolve with these re‐equilibration phenomena, with respect to the oil composition. Results of stretching simulations show a characteristic increase of T_h and ?_vap along correlation curves, with the curve shape dependent on petroleum composition. Leakage simulations show an increase of T_h and a smaller increase or even a decrease in ?_vap. Consequently, the better preserved inclusions in a given population can be presumed to be those that have the lowest T_h. Applications of T_h and ?_vap measurements of natural inclusions in calcite and in quartz showed that the fragility of the host mineral is a key factor allowing the recording of post‐entrapment events. Inclusions that have stretched or leaked are identified and the best preserved inclusions selected for evaluation of P–T–x trapping conditions. Moreover, petroleum types trapped in inclusions can be identified from ?_vap and T_h measurements without compositional modelling.