致密砂岩油藏CO₂驱微观剩余油赋存特征研究综述

A Review of Microscopic Remaining Oil Occurrence and Characterization in CO₂-Flooded Tight Sandstone Reservoirs

摘要: 针对致密砂岩油藏CO₂驱后微观剩余油赋存规律不明、驱替效率提升受限问题，本文系统综述了致密砂岩油藏CO₂驱微观剩余油的形成机理、赋存特征与演化规律，对比分析了聚焦离子束扫描电镜、CT扫描、核磁共振等核心表征技术的原理、优势与局限性，并探讨了当前研究瓶颈与未来发展方向。研究明确了微观剩余油的5类核心成因、3种孔喉尺度赋存类型及5种典型微观形态；CO₂驱不同阶段剩余油呈动态演化，初期优先动用大、中孔连续状剩余油，后期向微小孔喉及纳米孔富集，混相驱可有效降低储层动用下限。证实多技术联合的多尺度表征是突破单一方法局限的有效方法。本文的综述成果，可为致密砂岩油藏CO₂驱高效开发及剩余油挖潜提供一定的理论支撑。

Abstract: Given the unclear occurrence patterns of microscopic remaining oil and limited improvement of displacement efficiency in tight sandstone oil reservoirs after CO₂ flooding, systematically reviewed are the formation mechanisms, occurrence characteristics, and dynamic evolution of microscopic remaining oil during CO₂ flooding. Compared and analyzed are the principles, merits, and limitations of key characterization techniques, including focused ion beam-scanning electron microscopy (FIB-SEM), X-ray computed tomography (CT), and nuclear magnetic resonance (NMR), while current research bottlenecks and future development directions are discussed. Identified are five core formation mechanisms, three occurrence types by pore-throat scale, and five typical microscopic morphologies of remaining oil. Demonstrated is the dynamic evolution of remaining oil at different CO₂ flooding stages: the continuous oil phase in large and medium pores is preferentially displaced in the early stage, whereas remaining oil accumulates in micro-nano pore-throats in the late stage, and miscible flooding effectively lowers the minimum recoverable pore-throat size and improves displacement efficiency. Confirmed is that multi-technique integrated multi-scale characterization provides an effective approach for overcoming the limitations of single methods. The reviewed findings offer reliable theoretical support for the efficient development of CO₂ flooding, enhanced oil recovery, and remaining oil recovery in tight sandstone oil reservoirs.