Research paperSynthetic saline-aqueous and hydrocarbon fluid inclusions trapped in calcite at temperatures and pressures relevant to hydrocarbon basins: A reconnaissance study

- Fluid inclusions synthesized in calcite at conditions relevant to petroleum basins.
- Inclusions show high variability in measured homogenization temperature.
- Comparison of homogenization temperatures with the expected values.
- Little effect of hydrocarbons on homogenization behavior of aqueous inclusions.

We conducted reconnaissance experiments to synthesize aqueous and hydrocarbon inclusions trapped in calcite at conditions relevant to petroleum basins, and characterize the microthermometric properties of such inclusions. Fluid inclusions (FIs) were synthesized in a system of saline aqueous solution (5 or 20 wt% NaCl) coexisting with either heavy crude oil or gasoline under gas-undersaturated conditions, from 90 to 210 °C and 200-550 bar. The synthetic inclusions are not representative of gas-bearing systems, and methane (CH4) was not detected in any aqueous inclusions. The FIs are mainly distributed along planar healed cracks, indicating that the inclusions formed by fracture healing in the calcite crystal. Microthermometric measurements were conducted on coeval aqueous and hydrocarbon inclusions, and Raman spectroscopic analyses were done on aqueous inclusions, to determine the properties of FIs trapped at these conditions.Homogenization temperatures of synthetic FIs are mostly lower than the experimental trapping temperature, although the FIs show high variability in measured homogenization temperature. Results allow comparison of Th values for each sample with the expected Th, isochores and pressure corrections calculated for the system H2ONaCl. The latter parameters are broadly consistent with the known PVTX properties of H2ONaCl fluids, suggesting little effect of hydrocarbons on the homogenization behavior, although the low precision of the Th data limits this assessment. Nevertheless, this result is not unexpected considering that light hydrocarbons (gas) is not present in the experiments (as corroborated by Raman spectroscopy), a consequence of using “dead” oil in the experiments. Simulation of gas-bearing petroleum basins will require additional protocols for producing gas, either by in-situ cracking of the starting hydrocarbon material, or by other means. The reconnaissance experiments documented here provide a basis for such future experiments.