Physical simulation experiments on pore evolution in high-temperature and overpressure reservoirs

Abstract

At present, simulation on reservoir evolution under normal pressure is common while that under abnormal pressure is rare. In this paper, the Miocene “high-temperature and overpressure” reservoir in the Ledong–Lingshui Sag of the Qiongdongnan Basin was taken as the research object to quantitatively define the effects of high pressure and overpressure on the evolution of reservoir pores. After the temperature and pressure field in this area was divided in the setting of sedimentation and diagenesis, the evolution characteristics of pores in different temperature and pressure field were analyzed by means of natural analogy and physical simulation experiment. Then, the effects of overpressure and fluids on the evolution of reservoir pores were discussed. Finally, the main factors controlling the development of high-quality reservoirs were determined. And the following research results were obtained. First, the temperature and pressure field of the Miocene reservoir in the Ledong–Lingshui Sag can be divided into three zones, i.e., high temperature and normal pressure zone, high temperature and overpressure zone, and high temperature and super overpressure zone. Second, overpressure and super overpressure can provide some preservation on primary pores. In the same diagenetic stage, the plane porosity of overpressure and super overpressure reservoirs is 1.23–6.74% higher than that of normal pressure reservoirs. Once the reservoir pressure in overpressure and super overpressure areas is higher than hydrostatic pressure by 8 MPa and 4 MPa, respectively, about 1% primary pores are preserved. Third, the dissolution of organic acid makes greater contribution to the secondary pores in reservoirs and its plane porosity is 0.96–7.38% higher than that of normal compaction reservoirs. Fourth, the leaching effect of meteorological water on reservoir physical properties is slight, and its plane porosity is only 0.19% higher than that of normal compaction reservoirs. In conclusion, the dissolution of organic acid is the most constructive effect for the reservoirs in high temperature and normal pressure. In addition, preservation of primary pores by overpressure is the most constructive effect for the reservoirs in high temperature and (super) overpressure, and the higher the overpressure is, the more preservation effect it provides on pores.