Liu Huang, Tang Linwei, Huang Hao, Liu Hailong, Liu Minghao, Wang Qilin
National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China.
ACS Omega. 2025 Aug 13;10(33):37255-37265. doi: 10.1021/acsomega.5c02456. eCollection 2025 Aug 26.
Gas injection has been demonstrated as an effective method for enhancing recovery in low-permeability oil reservoirs, with its performance influenced by factors such as gas type, injection strategy, timing, and operational parameters. This study experimentally investigated the mechanism of oxygen-reduced air-water alternate flooding (WAG) in a low-permeability, heterogeneous light oil reservoir at the high water-cut stage. First, it was found that the dissolution of oxygen-reduced air slightly expands crude oil and enhances its fluidity. Nuclear magnetic resonance experiments revealed that oxygen-reduced air-heavy water alternate (WAG) flooding, following heavy water flooding, improved oil recovery in both high- and low-permeability parallel core samples. However, this method primarily displaced oil from larger pores. Furthermore, dual-core parallel flooding experiments demonstrated that water flooding followed by oxygen-reduced air (containing 5 mol % O)-water alternate flooding significantly enhanced oil recovery. Specifically, the low-permeability core achieved a maximum oil recovery of 69.33%, representing a 6.86% increase compared to single water flooding. Notably, this recovery even slightly surpassed that of the parallel high-permeability core (64.71%), attributable to low-temperature oxidation (LTO) reactions in the low-permeability cores. The LTO effect became more pronounced with higher oxygen concentrations in the injected gas. For practical applications, it is recommended to ensure sufficient contact time between oxygen-reduced air and crude oil within the reservoir to maximize oxidation reactions and improve oil recovery efficiency.
注气已被证明是提高低渗透油藏采收率的有效方法，其性能受气体类型、注入策略、时机和操作参数等因素影响。本研究通过实验研究了在高含水期低渗透、非均质轻质油藏中，脱氧空气-水交替驱（WAG）的驱油机理。首先，发现脱氧空气的溶解会使原油略有膨胀并提高其流动性。核磁共振实验表明，在重水驱之后进行脱氧空气-重水交替（WAG）驱，可提高高渗和低渗平行岩心样品的采收率。然而，该方法主要是从较大孔隙中驱替原油。此外，双岩心平行驱替实验表明，先水驱然后进行脱氧空气（含5 mol% O）-水交替驱可显著提高采收率。具体而言，低渗透岩心的最大采收率达到69.33%，比单一水驱提高了6.86%。值得注意的是，该采收率甚至略高于平行的高渗透岩心（64.71%），这归因于低渗透岩心中的低温氧化（LTO）反应。注入气体中的氧浓度越高，LTO效应越明显。对于实际应用，建议确保脱氧空气与油藏内原油有足够的接触时间，以使氧化反应最大化并提高采收率。
