Abstract:

CO₂ miscible displacement process has attracted wide attention of researchers in recent years due to its capacity on enhancing oil recovery. Comparative experimental investigations were carried out for oil recovery characteristics from water/oil pre-saturated porous medium with various displacement fluids of supercritical CO₂, supercritical CO₂ foam and N₂ foam. Referring to the reservoir temperature and pressure conditions, the enhanced oil recovery characteristics are analyzed and discussed in detail based on the displacement pressure drop along the core together with the extracted amount of oil from the porous medium. It is found the supercritical CO₂ fluid could achieve obviously higher oil recovery at the condition of 50℃ and 13 MPa. The fact that elevating the system pressure up to 23 MPa couldn't produce extra oil indicates the CO₂ displacing oil process achieves miscibility under the condition of 50℃ and 13 MPa in the porous media. The employments of other EOR methods of supercritical CO₂ foam and N₂ foam didn't produce more oil component from the sample. Compared to the result of 0.8 MPa for N₂ foam, the pressure drop for supercritical CO₂ foam flooding process is much lower at 0.3 MPa with poorer bubble generation performance. It is expected the experimental results could be employed on screening and evaluating supercritical CO₂ flooding technologies.

Key words: supercritical carbon dioxide, foam, multiphase flow, oil recovery characteristics

摘要：

CO₂混相驱替可以提高原油采收率，因此近年来得到研究者们的广泛关注。使用高温高压驱替设备，利用超临界CO₂流体、超临界CO₂泡沫及N₂泡沫作为驱替介质，对油水饱和孔隙介质中的油相驱替特性开展了比较实验研究。通过对驱替过程沿程压力及对驱替增采油量的测量，对不同驱替手段在孔隙介质内的油相增采特性进行深入研究和探讨。研究发现在温度为50℃、压力为13 MPa时，超临界CO₂流体对多孔介质内的油相驱替效果有显著提升，当压力进一步升高到23 MPa时，油相增采效果不明显。说明在本实验条件下超临界CO₂流体与油相在50℃、13 MPa时可达到混相驱替状态；而采用超临界CO₂泡沫及N₂泡沫注入工艺未能进一步提高出油量。沿程压差测量结果则显示，与N₂泡沫相比，超临界CO₂泡沫在多孔介质试样内的驱替压差较小，起泡性能较差。实验结果对于筛选及评价超临界CO₂驱油工艺具有一定的指导意义。

关键词: 超临界二氧化碳, 泡沫, 多相流, 驱油特性