缝洞型碳酸盐岩油藏注气吞吐EOR效果评价

缝洞型碳酸盐岩稠油油藏以大型溶洞、溶蚀孔洞及裂缝为主要储集空间，非均质性极强，针对此类油藏，注气吞吐是一种有效的开发方式。为了探索缝洞型碳酸盐岩油藏注气吞吐开发效果，设计并制作了适用于缝洞型油藏吞吐室内物理模拟实验装置，从换油率、产气速率、产气量等方面对比分析了4种吞吐介质（CO₂、N₂、先注CO₂后注N₂、先注N₂后注CO₂）的吞吐效果，分析了作用机理。实验结果表明：注气吞吐提高采收率效果显著，最低换油率的N₂吞吐也能达到0.422；CO₂与N₂混合气吞吐中，CO₂溶于原油中能使其黏度降低，N₂由于重力分异作用占据缝洞高部位形成气顶，这种协同作用使得CO₂与N₂混合气吞吐效果好于单一注气吞吐；而在注气顺序上先注N₂后注CO₂吞吐效果更加明显，换油率可达0.861。缝洞型油藏注气吞吐开采是一种行之有效提高采收率的方法，先注N₂后注CO₂混合气吞吐可获得更显著的开发效果。

Evaluation of EOR Effect of Gas Huff-n-puff in Fractured Vuggy Carbonate Reservoirs

Large water-eroded caves, solution pores, and fractures are the main spaces of fractured vuggy carbonate reservoirs with strong heterogeneity. The technology of gas huff-n-puff is an effective way to improve oil recovery in such reservoirs. In this study, an indoor physical simulation apparatus was designed and produced for carbonate reservoirs in order to explore the huff-n-puff effect of different gases. The huff-n-puff effect and its mechanism for four gases(CO₂, N₂, CO₂ injected before N₂, CO₂ injected after N₂) were analyzed considering the parameters of oil change rate, gas generation rate, and cumulative gas production. The experimental results show that the huff-n-puff mechanism of the four injected gases is obvious. The lowest oil change rate was 0.422(N₂ huff-n-puff). The mixed gas (CO₂ and N₂ mixture) huff-n-puff fully develops a synergistic effect. CO₂ dissolved in crude oil decreases oil viscosity, while N₂ occupies the high positions of caves and forms a gas cap due to gravitational differentiation. The huff-n-puff effect of the gaseous mixture of CO₂ and N₂ is better than that of a single gas, and CO₂ injection after N₂ huff-n-puff can achieve the best effect with an oil change rate of 0.861. Experimental research shows that gas huff-n-puff is an effective EOR, and the huff-n-puff effect of CO₂ injected after N₂ is more remarkable.