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

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 degrees 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. Micro thermometric 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 T-h values for each sample with the expected T-h, isochores and pressure corrections calculated for the system H2O-NaCl. The latter parameters are broadly consistent with the known PVTX properties of H2O-NaCl fluids, suggesting little effect of hydrocarbons on the homogenization behavior, although the low precision of the T-h 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. (C) 2016 Elsevier Ltd. All rights reserved.