Reconstruction of paleo-temperature and pressure of oil reservoirs based on PVTx simulation: problems, strategies and case studies

The PVTx simulation of fluid inclusions is a valuable method for the reconstruction of paleo-temperature and pressure of oil reservoir. Since the accurate composition of oil-bearing inclusion is very difficult to be obtained and the composition may be altered during secondary alteration processes, it may cause uncorrected results. Compared to oil-bearing inclusion, the composition of accompanied aqueous inclusion is relatively simple and could hardly be affected during secondary alteration processions. As a result, accompanied aqueous inclusions were applied to reconstruct the paleo-temperature and pressure of well SN 1 in the South Shuntuoguole area of Tarim Basin. Gas-oil-bitumen bearing inclusions and aqueous inclusions are co-existed in calcite veins of well SN 1. The homogenization temperatures of aqueous inclusions were higher than 170℃, and the homogenization pressure of aqueous inclusions is significantly fluctuating from 39.1 MPa to over 165.8 MPa. The unusually high homogenization temperature of aqueous inclusions may be caused by hydrothermal fluid activity while the fluctuation of homogenization pressure of aqueous inclusions may be caused by oil cracking. The lowest homogenization pressure of aqueous inclusion was applied to determine the charge time of hydrothermal fluid, which is Hercynian. The charging time of hydrothermal fluid is in accordance with the active time of NE-trending strike-slip faults in the South Shuntuoguole area. Thus, the co-existing aqueous inclusions potentially can be applied to reconstruct the paleo-temperature and pressure of oil reservoir to make up the deficiency of present methods.