CO2 flooding is one of the main methods to enhance oil recovery under the background of carbon neutralization and carbon peak. In some fields, however, injected gas is mainly produced gas that contains a lot of acid gas. The EOR effect of acid gas flooding is rarely mentioned in the literature. Therefore, it is necessary to study the displacement process of acid gas flooding. In this paper, acid gas composed of H2S and CO2 is studied. Oil samples from typical blocks of T reservoir are selected to study the EOR effect of acid gas. Under different displacement pressure, different proportions of acid gas were used to carry out slim tube experiments. The percentages of H2S and CO2 in acidic gases are 0%, 20%, 40%, 50%, 60%, 80% and 1, respectively. The experimental process is to fill the tube with crude oil and then flood the oil with acid gas with different proportions of H2S and CO2 content at a constant temperature. The ultimate recovery factor is the displacement efficiency, obtained at 1.2 pore volume gas injection or without oil production. Displacement experiments under different pressures were also carried out. The results show that the displacement efficiency increases with the increase of displacement pressure at the same temperature, oil composition and gas composition. The experimental results also show that, at the same temperature, oil composition and displacement pressure, displacement efficiency increases with the increase of the proportion of acid gas in the injected gas. The production gas of high sulfur gas field is injected back into the formation theoretically, and the effect of acid gas mixed displacement composed of H2S and CO2 is studied, which provides a new direction for the application of H2S and CO2.
Keywords acid gas flooding, EOR, displacement pressure, displacement efficiency