PDF(Pubmed)
Abstract：
After polymer flooding, the heterogeneity between different layers intensifies, forming intricate seepage channels and fluid diversions, which results in decreased circulation efficiency and lower recovery rates, leaving a significant amount of residual oil trapped within the reservoir. Understanding the characteristics of residual oil occurrence is crucial for enhancing oil recovery post-polymer flooding. This study focused on sandstone reservoirs with varying permeability in the Saertu block of the Daqing oilfield. Using cryosectioning and laser scanning confocal microscopy, the occurrence characteristics of the residual oil in these sandstone reservoirs post-polymer flooding were investigated. Additionally, micro-CT and scanning electron microscopy were employed to analyze the impact of the pore structure on the distribution characteristics of the residual oil. The results indicate that laser scanning confocal images reveal that post-polymer flooding, the residual oil in high- and low-permeability sandstone reservoirs predominantly exists in a bound state (average > 47%), mostly as particle-adsorbed oil. In contrast, the residual oil in medium-permeability reservoirs is primarily in a free state (average > 49%), mostly as intergranular-adsorbed oil. In high-permeability sandstone reservoirs, heavy oil components are mainly in a particle-adsorbed form; in medium-permeability sandstone reservoirs, residual oil predominantly consists of heavy components, with most light components occurring in a clustered form; in low-permeability sandstone reservoirs, clustered residual oil exists in a balanced coexistence of light and heavy components, while the heavy components primarily exist in a particle-adsorbed form. Post-polymer flooding, the large pore-throat structure in high-permeability sandstone reservoirs results in effective displacement and less free residual oil; medium-permeability sandstone reservoirs, with medium-large pores and throats, have preferential channels and fine particles blocking the throats, leading to some unswept pores and more free residual oil; low-permeability sandstone reservoirs, with small pores and throats, exhibit weak displacement forces and poor mobility, resulting in more bound residual oil. The distribution and content of clay particles and clay minerals, along with the complex microscopic pore structure, are the main factors causing the differences in the residual oil occurrence states in sandstones with varying permeability.
摘要：
聚合物驱油后,不同层之间的异质性加剧，形成复杂的渗流通道和流体分流，这导致循环效率降低和回收率降低，留下大量的残留油被困在储层内。了解剩余油的赋存特征对于提高聚合物驱后的采收率至关重要。本研究主要针对大庆油田萨尔图区块不同渗透率的砂岩油藏。使用冷冻切片和激光扫描共聚焦显微镜，研究了聚合物驱后砂岩油藏剩余油的赋存特征。此外,利用显微CT和扫描电镜分析了孔隙结构对剩余油分布特征的影响。结果表明，激光扫描共焦图像揭示了聚合物驱后，高、低渗透砂岩油藏的剩余油主要以结合态存在(平均>47%)，主要是颗粒吸附油。相比之下,中渗透油藏的剩余油主要处于自由状态(平均>49%)，主要作为晶间吸附油。在高渗透砂岩储层中,稠油组分主要以颗粒吸附形式存在；在中等渗透砂岩油藏中，渣油主要由重质成分组成，大多数轻组分以集群形式出现；在低渗透砂岩储层中，簇状渣油存在于轻质和重质组分的平衡共存中，而重质组分主要以颗粒吸附形式存在。聚合物后驱油,高渗透砂岩储层的大孔喉结构导致有效驱替和较少的游离剩余油；中渗透砂岩储层，有中等大的毛孔和喉咙，有优先通道和细小颗粒阻塞喉咙，导致一些未清扫的孔隙和更多的自由剩余油；低渗透砂岩储层，有小毛孔和喉咙，表现出较弱的位移力和较差的机动性，导致更多的结合残留油。粘土颗粒和粘土矿物的分布和含量，随着复杂的微观孔隙结构，是导致不同渗透率砂岩剩余油赋存状态差异的主要因素。
