Calculation of paleo-pressure in gas reservoirs using fluid inclusions

Trapping pressure and trapping temperature of fluid inclusions are important information for the research of petroleum charge history which represents the paleo-pressure and paleo-temperature of gas-oil reservoirs. Gas-bearing (e.g., CH₄) inclusions are common in gas reservoirs. The difficulty for the determination of trapping pressure and temperature of inclusions is to accurately measure the concentration of methane. We propose a feasible and credible way to calculate inclusion trapping pressures by using an iteration calculation model based on the hypothesis of constant total volume and composition of intact inclusions and correlation curves of inclusion pressure at room temperature and the Raman shift of methane gas. The method was applied to paleo-pressure of fluid inclusions trapped in the Baota Formation limestones in well Long32 in the southern Sichuan. Results indicated that the trapping pressure is in the range of 884.08-1249.32 bar, which is an overpressure circumstance at a pressure factor of 1.3-1.8.