Physical simulation experiment on porosity evolution and controlling factors of Miocene reservoir in Ledong-Lingshui Depression, Qiongdongnan Basin, South China Sea

Abstract

Considering the high-temperature and overpressure in Miocene reservoirs of Ledong-Lingshui Depression, physical simulation experiments and other methods were adopted to identify the effect of overpressure on reservoir quality and the controlling factors of high-quality reservoir in porosity evolution process. In this paper, the temperature-pressure fields were divided into high-temperature normal-pressure (HTNP) zone, high-temperature overpressure (HTOP) zone, and high-temperature high-overpressure (HTHO) zone. The research findings are as follows: (1) The overpressure has a certain protective effect on primary pores. The visible porosity obtained from overpressure compaction simulation experiment is much higher than that obtained from normal compaction simulation experiment in the same diagenetic stage. The differences of visible porosity between normal compaction and overpressure compaction and high overpressure compaction can reach 1.55% and 6.74% respectively. (2) The organic acid dissolution contributes greatly to the formation of secondary pores in reservoir. The difference of visible porosity between organic acid dissolution and normal compaction is 0.96–7.38%. But the meteoric water leaching has a limited impact on reservoir porosity with a difference of merely 0.19% between meteoric water leaching and normal compaction. (3) Organic acid dissolution has the greatest constructive effect on diagenesis under the HTNP. However, overpressure protection to primary pores is the leading contributor to high-quality reservoir under the HTOP and HTHO, and the protective effect is positively correlated with the increase of overpressure. Overall, this work provides new insights into the porosity evolution and controlling factors in reservoirs.