Feasibility study on further enhanced oil recovery by ISC of remaining oil after polymer flooding

The residual oil after polymer flooding in China is highly dispersed. The reservoir's interlayer and intralayer contradictions are prominent, the polymer flooding efficiency is significantly reduced, and the exploitation difficulty is increased. An indoor physical simulation experiment of undertaking fire flooding after polymer flooding is conducted to investigate the recovery measures that can undertake polymer flooding and further improve the recovery degree of residual oil. The stability of the combustion front and the basic parameters of in situ combustion (ISC) were studied, and the crude oil properties before and after the fire flooding were analyzed. The results show that the temperature range and variation trend of the combustion front in the polymer flooding-to-fire flooding experiment are similar to those in the conventional fire flooding experiment. The combustion front advances steadily, indicating that the residual oil can be burned effectively after polymer flooding, providing an application basis for fire flooding. The calculated apparent H/C atomic ratio through the tail gas composition is 1.33, which further demonstrates that a high-temperature oxidation reaction occurs at the combustion front, and the displacement efficiency of the burned oil layer is 72.1%. A comparison of the oil samples before and after fire flooding shows that the carbon number of n-alkanes in the oil produced after fire flooding increases, improving the quality of crude oil.