摘要：

缝洞型碳酸盐岩油藏区别于普通油藏，具有储集体空间分布不连续、有效储集空间尺度差异大、内部结构与缝洞接触关系复杂、不同储集单元存在不同的油水分布关系、内部油气渗流规律复杂等特点，而注水和注气方式是高效开发缝洞型碳酸盐岩油藏的重要方式，针对缝洞型碳酸盐油藏注水、注气转换时机不清，导致现场注气开发过程中无法有效确定注气时机的问题。国内外缝洞型碳酸盐岩油藏物理模拟研究采用的模型存在只能在可视化与高温高压中取其一，研究角度不够全面的问题。本文针对上述问题，基于相似原则自主研制了高温高压二维缝洞型油藏可视化物理模型，采用该模型开展注水与注气驱油实验，探究注水、注气驱油过程中缝-洞模型内部油-气-水渗流规律，评价不同注水、注气转换时机与不同注水位置对实验驱替效率的影响，厘清注水与注气关系，明确注气转注时机与剩余油空间展布特征。实验结果表明：1) 通过缝洞型可视化模型注水转注氮气开发实验研究，明确注水转注氮气开发方式是缝洞型油藏有效的开发方式，在水驱作用特征及氮气气顶驱机理的协同作用下，获得较高的驱油效率，达到67.67%。2) 通过不同注采方式实验研究，研究表明缝洞油藏注水驱开发过程中，与高注低采开发方式相比较，低注高采开发方式水驱波及面积更大，水驱作用发挥更充分，获取更高的驱油效率，整体驱油效率提高了2%~4%。3) 对比不同注氮气转注时机驱油效果，优选注采方式为低注高采，氮气转注时机为注水1 PV后转注氮气，获得最高的驱油效率。4) 缝洞型储集体水驱开发结束后，剩余油分布形式主要以“油膜”、“阁楼油”、“绕流油”为主；气驱阶段结束后，剩余油分布形式主要以“界面油”、“绕流油”与“油膜”分布为主。本研究成果有助于探究缝洞型碳酸盐岩油藏注水与注气提采机理，明确转注时机与剩余油分布规律，为缝洞型油藏气驱开发方案优化、剩余油挖潜提供理论依据。

关键词: 缝洞型油藏, 高温高压可视化, 注气时机, 驱油特征, 剩余油空间展布

Abstract:

Fractured-vuggy carbonate reservoirs differ from conventional reservoirs by exhibiting characteristics such as discontinuous spatial distribution of reservoir bodies, significant variations in effective storage space scale, complex internal structures and fracture-cavity connectivity, heterogeneous oil-water distribution relationships among different reservoir units, and complicated hydrocarbon flow mechanisms. Water flooding and gas injection serve as important methods for efficient development of fractured-vuggy carbonate reservoirs. However, the unclear timing for switching between water flooding and gas injection in fractured-vuggy carbonate reservoirs leads to difficulties in determining the optimal gas injection timing during field gas injection operations. Meanwhile, existing physical simulation models for fractured-vuggy carbonate reservoirs worldwide can only achieve either visualization or high-temperature-high-pressure conditions, resulting in insufficiently comprehensive research perspectives. To address these issues, this study independently developed a high-temperature-high-pressure two-dimensional visual physical model of fractured-vuggy reservoirs based on similarity principles. Using this model, we conducted water flooding and gas displacement experiments to investigate oil-gas-water flow mechanisms during the displacement process in fracture-cavity systems, evaluate the effects of different water-gas switching timings and various water injection positions on displacement efficiency, clarify the relationship between water and gas injection, and determine the optimal gas injection timing and spatial distribution characteristics of remaining oil. The experimental results show that: 1) Through water flooding followed by nitrogen injection experiments in the visual fractured-vuggy model, we confirmed that this method represents an effective development approach for fractured-vuggy reservoirs. Under the synergistic effects of water flooding characteristics and nitrogen gas-cap drive mechanisms, a high displacement efficiency of 67.67% was achieved. 2) Comparative experiments on different injection-production methods demonstrated that during water flooding development of fractured-vuggy reservoirs, the low-injection-high-production method provided larger water flooding sweep area and more effective water flooding performance compared with the high-injection-low-production method, resulting in 2%~4% higher overall displacement efficiency. 3) By comparing oil displacement effects under different nitrogen injection timings, the optimal development method was determined to be low-injection-high-production with nitrogen injection initiated after 1 PV of water flooding, which yielded the highest displacement efficiency. 4) After water flooding development in fractured-vuggy reservoirs, remaining oil primarily distributed as “oil films,” “attic oil,” and “bypassed oil.” Following gas flooding, the main remaining oil distribution patterns were “interfacial oil,” “bypassed oil,” and “oil films.” These research findings contribute to understanding the enhanced oil recovery mechanisms of water and gas injection in fractured-vuggy carbonate reservoirs, clarifying the optimal switching timing and remaining oil distribution patterns, and providing theoretical guidance for optimizing gas flooding development plans and remaining oil potential exploitation in fractured-vuggy reservoirs.

Key words: fractured-vuggy reservoir, high temperature high pressure visual model, timing of gas injection, flooding characters, distribution of residual oil

中图分类号: 

• TE327

• P618.13