Long-core experimental study of different displacement modes on fractured-vuggy carbonate reservoirs

Abstract

It is difficult to utilize real fractured–vuggy carbonate cores to conduct long-core displacement experiments due to the special structures of fractured and vuggy. Aiming to not affect the porosity and permeability of the original core structure, a special filling method on the sunken space of the core surface was created to meet the requirements of long-core experiments. Long-core experiments of depletion drive, water flooding, gas drive, and water alternating gas (WAG) drive were performed to simulate the actual conditions of one-dimension oil reservoir and systematically study the influence of different development approaches on the recovery of vuggy carbonate reservoirs. Results show that the optimal conversion pressure of water flooding is between 80% bubble point and bubble point pressure. In the high-pressure and high water-cut stage, the development effect of gas–water alternative drive becomes significant, it can effectively reduce water cut and improve oil recovery. The most suitable and effective displacement mode is adopted depletion drive first and converts water flooding when the pressure decreases between 80% bubble point and bubble point pressure. When the water cut approximately reaches 80%, then WAG flooding is performed. The experiments provide data and technical support for the rational development of vuggy carbonate reservoirs.