致密砂岩油藏超临界与非超临界CO2驱油特征

细管驱替实验结果表明陕北某致密砂岩油藏在实施CO₂驱时无法达到混相。为了明确非混相驱下CO₂超临界性质对驱油贡献的大小及对驱油特征的影响规律，开展了室内超临界和非超临界CO₂驱油实验研究。结果表明：CO₂超临界性质对驱油具有积极影响，在超临界压力点附近，压力由非超临界过渡到超临界的较小变化会引起驱油特征的明显改变。当累积注入量达到0.5 PV以后，CO₂超临界驱油效果明显好于非超临界驱油效果；超临界驱体现优势的阶段主要是CO₂注入量为0.5～1.5 PV时，相同条件下采出程度比非超临界驱最高高出约10%。超临界驱和非超临界驱换油率出现高峰的注入时段基本都在注入量约为1 PV时，但前者明显高于后者。总之，无论是在注入性能方面，还是在驱油效率和换油率等方面，超临界驱均优于非超临界驱。

Supercritical and non-supercritical CO2 flooding characteristics in tight sandstone reservoir

Slim tube displacement test results indicate that CO₂ miscible flooding in tight sandstone reservoir in northern Shaanxi cannot be implemented. In order to define the contribution and the influence rule of supercritical CO₂ properties on displacement characteristics in the condition of immiscible flooding,supercritical and non-supercritical CO₂ oil displacement experiments were conducted. The results show that supercritical state of CO₂ has a positive influence on oil displacement,and the small change of pressure near by the supercritical pressure point from non-supercritical to supercritical can bring a great difference of driving characteristics. After 0.5 PV cumulative injections,the effect of supercritical CO₂ flooding is significantly better than that of non-supercritical flooding. The advantage stage for supercritical flooding is mainly when the cumulative CO₂ injections reach between 0.5 PV and 1.5 PV,the recovery is about 10% higher than that of non-supercritical flooding under the same conditions. The oil change ratio of supercritical flooding and non-supercritical flooding occurs peak nearly at the same injection time (about 1 PV), but the former is significantly higher than the latter. In short,whether in the injection performance,or in the oil displacement efficiency and oil change ratio,supercritical flooding is better than non-supercritical flooding.