超低渗油藏超临界CO_(2)驱油特征及原油动用能力

Displacement Characteristics and Capacity of Supercritical CO_(2) Flooding in Ultra Low Permeability Reservoirs

为明确超临界CO_(2)驱替特征,结合核磁共振技术对比了超低渗透油藏超临界CO_(2)非混相、混相驱及水驱对储层孔隙原油动用效果,明确了长庆超低渗油藏岩心内原油分布特征,对比了不同注入介质对不同孔喉内原油采出程度的贡献程度。结果表明:超临界CO_(2)混相及非混相驱的见气阶段是采出程度迅速增加阶段,气窜后驱油效率大幅降低,对比了不同驱替方式采出程度,油藏条件下水驱主要动用大、中孔隙;CO_(2)非混相驱主要提高中、小孔的采出程度;水驱及非混相驱均无法动用小于0.1μm的微孔内原油;而CO_(2)混相驱对小、微孔提升较大,在混相气驱后,大、中孔隙动用程度接近100%,小孔和微孔分别达到34%和10%。混相气驱效果最佳,其次为非混相驱与高压水驱,低压水驱对原油动用能力较差。研究为超低渗油藏驱油方式的选择提供了理论依据。

In order to reveal the mechanism of supercritical CO_(2) displacement charateristics,nuclear magnetic resonance(NMR)technology was employed to compare the effect of supercritical CO_(2) immiscible/miscible flooding with simple water flooding on oil displacement efficiency in ultra-low permeability reservoirs.The distribution characteristics of crude oil in the core samples in Changqing ultra-low permeability reservoir were clarified,and the contribution of different injection media to the production degrees of crude oil in different sizes of pore throat were compared.The results show that the gas emergence stage for both supercritical CO_(2) miscible and immiscible flooding is the stage of production degree rapid increase,and the oil displacement efficiency decreases rapidly after gas channeling.The results of oil recovery factor for different displacement mode are that water flooding mainly displace the oil in large and medium pores,and CO_(2) immiscible flooding mainly improves the recovery degree of medium and small pores.Both water flooding and immiscible flooding can not move the oil in the micropores less than 0.1μm.CO_(2) miscible flooding can improve the recovery degree in small and micro pores significantly.After miscible gas flooding,the recovery factor of large and medium pores is close to 100%,and the small pores and micro pores can reach 34%and 10%,respectively.Miscible CO_(2) flooding is the best,followed by immiscible CO_(2) flooding and high pressure water flooding,and the low pressure water flooding is the lowest.The study provides a theoretical basis for the selection of oil displacement mode in ultra-low permeability reservoirs.