【摘要】 针对裂缝性致密油藏注气开发中重力分异弱、气窜率高及碳封存机制不清的问题,提出了采用CO₂-N₂混合气顶部注气重力驱的开发方法,并系统探究其提高采收率与CO₂封存的协同机理。通过耦合改进的Peng-Robinson状态方程与CoolProp热力学库,构建了CO₂-N₂混合气的相态模型,并结合离散裂缝网络（DFN）建立了裂缝性致密油藏组分数值模拟模型。利用该模型,系统研究了混合气配比、注采参数及裂缝特征对驱油与碳封存效果的影响机制,并优化了关键参数。研究结果表明,当CO₂摩尔分数为70%时,混合气与原油密度差达330.2 kg/m³,重力分异效果最优;在裂缝密度为0.05条/m的储层中,采用顶部注气方式,以2×10⁴ m³/d的注气速度及250 m的注采井距进行开发,最终采收率较衰竭开发提高27.3%,同时可实现8.7×10⁴t的CO₂封存量。碳封存主要通过溶解捕集与残余孔隙捕集实现,封存效率随裂缝连通性增强呈先增后减趋势,在20 MPa、57℃的储层条件下可实现CO₂长期稳定封存。本研究明确了CO₂-N₂混合气重力驱在裂缝性致密油藏中“驱油-封存”协同的机理与潜力,为同类油藏的高效开发与碳封存协同实践提供了技术支撑。更多还原

【Abstract】 To address the challenges of weak gravity segregation,high gas channeling risk,and unclear carbon sequestration mechanisms during gas injection in fractured tight oil reservoirs,a method utilizing CO₂-N₂ mixed gas top injection gravity drainage is proposed.This study systematically investigates the synergistic mechanism of enhanced oil recovery and CO₂ sequestration.By coupling a modified Peng-Robinson state equation with CoolProp thermodynamic module,a phase-behavior model for CO₂-N₂ mixed gas was established.Incorporating with a discrete fracture network（DFN）,a compositional numerical simulation model for fractured tight oil reservoirs was constructed.By using this model,the impact of mixed gas composition,injection-production parameters,and fracture natures on oil displacement and CO₂ sequestration was studied,and key parameters were optimized.Results show that optimal gravity segregation occurs at a CO₂ molar fraction of 70%,yielding a density difference of 330.2 kg/m³ against crude oil.In the reservoirs with fracture density of 0.05 fractures·m^-1,top gas injection engaged at a rate of 2×10⁴ m³/d with a injection-production well spacing of 250 m improves the ultimate recovery by 27.3% compared to depletion development.Moreover,8.7×10⁴ t CO₂ sequestration is achieved Carbon sequestration is primarily achieved through dissolution trapping and residual pore trapping,with sequestration efficiency showing a trend of first increasing and then decreasing with fracture connectivity.Long-term stable CO₂ sequestration is achievable under reservoir conditions of 20 MPa and 57 ℃.This research determines the synergistic mechanism and prospect of CO₂-N₂ mixed gas gravity drainage for oil displacement and carbon sequestration in fractured tight oil reservoirs and provides technical support for the synergistic practice of field development and carbon sequestration in similar reservoirs.更多还原