【摘要】 低渗透油藏注CO₂开发可协同实现提高原油采收率（EOR）和碳封存的双重目标，但其驱替过程中CO₂与原油的混相状态受含水饱和度影响显著。为了明确低渗透油藏不同含水阶段CO₂驱的多类型混相特征及其对驱油和碳封存效果的影响，开展了CO₂-原油相态实验，建立了低渗透油藏CO₂驱数值模拟组分概念模型，提出了不同含水饱和度条件下CO₂-原油多类型混相状态定量划分标准及表征方法，揭示了含水饱和度对混相压力动态界限的影响规律，指导了CO₂-EOR油藏工程方案的优化设计。研究结果表明：（1）基于界面张力和采收率变化规律，可将低渗透油藏CO₂驱混相状态划分为非混相、近混相、混相和完全混相4种类型，并提出了划分界限；（2）含水饱和度升高会导致最小混相压力阈值上升，混相压力区间缩小，同时削弱了CO₂传质作用，降低了原油流度改善效果，最终致使原油采收率下降；（3）向CO₂中添加15%（C₂～C₆）烃类混合气或采用3∶1注采比，可有效提升混相程度，使原油采收率较常规水气交替驱方案分别提高3.90%和2.99%。结论认为：（1）在低渗透油藏CO₂-EOR油藏工程方案设计时，应优先聚焦中低含水饱和度区块，通过优化注采参数以实现完全混相驱；（2）在中高含水饱和度区块应以近混相或混相驱为主，可获得较高的原油采收率并降低开发成本，实现经济效益最大化。更多还原

【Abstract】 CO₂ injection into low-permeability oil reservoirs can realize the dual goals of enhanced oil recovery（EOR） and carbon storage. In the process of CO₂ flooding, however, the mixed-phrase state of CO₂ and crude oil is significantly influenced by water saturation. To elucidate the multi-type miscibility characteristics in low-permeability oil reservoirs under varying water saturation conditions during CO₂ flooding and their influence on oil displacement and carbon storage, this paper carries out CO₂-crude oil phase state experiments, establishes a compositional conceptual model for numerical simulation of CO₂ flooding in low-permeability oil reservoirs, and proposes quantitative classification criteria and characterization method for CO₂-crude oil multi-type miscibility states with varying water saturation, which reveals the influence laws of water saturation on dynamic limit of miscibility pressure, and provides a guidance for optimizing the design of CO₂-EOR reservoir engineering scheme. The following results are obtained. First, based on the change laws of interfacial tension and recovery efficiency, the miscibility states in low-permeability oil reservoirs during CO₂ flooding can be classified into four types, i.e., immiscible, near-miscible, miscible and fully miscible, and the classification criteria are defined. Second, higher water saturation can increase the minimum miscibility pressure threshold and narrow the miscibility pressure interval, while weakening CO₂ mass transfer and oil mobility improvement effect, so as to ultimately decrease the recovery efficiency. Third, adding 15%（C₂-C₆） hydrocarbon gas mixture into CO₂ or adopting an injection/production ratio of 3:1 can effectively increase the miscibility degree, enhancing the oil recovery by 3.90% and 2.99% respectively, compared with that of conventional WAG scheme. In conclusion, when designing a reservoir engineering scheme for CO₂-EOR of low-permeability oil reservoirs, priority shall be focused on the blocks with medium-low water saturation to realize fully miscible flooding by optimizing injection and production parameters. What’s more, as for the blocks with medium-high water saturation, it is necessary to take near-miscible or miscible flooding as the dominant mode, which can achieve higher oil recovery and lower development costs, maximizing the economic benefit.更多还原