缝洞型碳酸盐岩油藏氮气驱效果影响因素

Influencing factors of the effect of nitrogen gas drive in fractured-vuggy carbonate reservoir

缝洞型碳酸盐岩油藏以大型溶洞、溶蚀孔洞及裂缝为主要的储集空间,具有非均质性强、缝洞结构复杂的特点,气驱是该类油藏重要的开发方式之一。为探索缝洞型碳酸盐岩油藏气驱动态特征、驱油效果的影响因素及规律,建立二维典型缝洞可视化模型,研究不同类型剩余油启动效果,并结合氮气驱物理模拟驱油效果定量对比,分析氮气驱效果的影响因素。研究结果表明:氮气驱可进一步启动水驱未波及区域的剩余油;氮气驱效果及油、气、水流动特征受到溶洞充填方式、原油粘度和底水能量等因素影响,溶洞充填方式主要影响流体的渗流特征,在一定程度上有利于扩大氮气驱波及范围;原油粘度和底水能量影响氮气和底水的相互作用,改变压力场的分布;在强底水作用下,水窜更为明显,但能改善氮气驱效果,提高采收率。

Fractured-vuggy carbonate reservoir has the features of strong heterogeneity and complex structure,whose reservoir space is mainly large caves,solution pore and fractures. Gas flooding is one of the important methods of development in this type of oil reservoir. In order to probe dynamic features,influencing factors and rules of gas flooding in the fracturedvuggy carbonate reservoir,a typical 2D visual model of fracture-vug was built to study the development of remaining oil of various types. Physical simulation experiments of nitrogen gas flooding were carried out to study the influencing factors of the nitrogen gas drive. The research results show that the nitrogen gas drive can activate the remaining oil of unswept areas during water flooding. The effect of nitrogen gas drive and flow characteristics of oil,gas and water are influenced by cavityfilling type,crude oil viscosity and energy of bottom water. The cavity-filling type mainly affects the percolation characteristic of the fluid and is beneficial to enlarge swept volume of the nitrogen gas flooding to a certain extent. The crude oil viscosity and the energy of bottom water affect the interaction between the nitrogen gas and bottom water,which may change the distribution of pressure field. Bottom water with strong energy will accelerate water breakthrough,but it can improve the effect of the nitrogen gas drive and oil recovery.