Abstract:

The CO₂ miscible flooding project in the Taizhou formation of Caoshe oilfield is one of the most successful CO₂ EOR projects in China. The feasibility study on the secondary miscible flooding was carried out to settle the issues of complex remaining oil distribution and severe gas channeling in the later stage after first miscible flooding. The characteristic of microscopic fractal dimension in the CO₂ miscible flooding process of real core sample was observed through metalloscope. The remaining oil types attaching to the pore surface of rock took on the forms of thin film and isolated beads. The displacement efficiency of the secondary CO₂ miscible flooding was 93.4 %, which was 9.73 % higher than that of the first CO₂ miscible flooding. The average residual oil saturation was 30.8 % in sealed coring test, indicating great potential of III formation. A feasible development plan for secondary miscible-phases flooding was proposed to develop the stratified reservoirs at the bottom position. The CO₂ injection on the higher position was adopt to suppress gas gravity overlap, and the water alternating gas was applied to slow down the gas channeling. Furthermore, the injection profile was adjusted during the whole process of gas injection. The incremental recovery ratio was estimated to be 8 % ~ 10 %.

Key words: Taizhou formation in Caoshe oilfield, CO₂ flooding, first miscible-phases flooding, secondary miscible-phases flooding