Liao Hengjie, He Xianke, Guo Ping, Wang Shuoshi, Li Yuansheng, Jiang Zhehao, Wang Limiao, Xu Ruifeng, Tu Hanmin
Shanghai Branch of CNOOC Limited, Shanghai 200335, China.
National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China.
ACS Omega. 2024 Oct 19;9(43):43850-43863. doi: 10.1021/acsomega.4c06866. eCollection 2024 Oct 29.
During the depletion and pressure reduction process in condensate gas reservoirs, the precipitation of condensate oil transforms the single-phase gas flow into a two-phase gas-liquid flow, significantly reducing the permeability. Currently, microscopic studies of the phase behavior of condensate gas in porous media mainly focus on observing and describing the occurrence of condensate oil, lacking quantitative calculations and direct observations of condensate oil throughout the entire depletion cycle. This paper uses a microvisualization method to simulate the depletion process of condensate gas reservoirs. Condensate gases with oil contents of 175.3 and 505.5 g/cm were prepared by mixing methane, ethane, hexane, and decane in specific proportions. Pore structures were extracted from thin sections of real core casts, and microfluidic chips with a minimum pore diameter of 20 μm and an areal porosity of 20.75% were fabricated by using a chemical wet etching method. Subsequently, microfluidic condensate gas depletion experiments were conducted with chip images recorded during the depletion process. Grayscale analysis of the depletion images was performed using ImageJ software to quantitatively calculate condensate oil saturation and recovery rates, analyzing the effects of different condensate oil contents on condensate gas depletion, and comparing the differences between depletion in porous media and in a PVT cell. The conclusions drawn are as follows: the dew points of high and low in the porous media are 3.15% and 1.85% higher than those in the PVT cell, respectively. In the early stages of depletion, condensate oil saturation in porous media is higher than that in the PVT cell, while in the middle to late stages, condensate oil saturation in porous media is lower than that in the PVT cell. The condensate oil recovery rate in porous media is significantly higher than the depletion recovery rate in the PVT cell. Condensate oil tends to precipitate and disperse at blind ends and corners, while it easily forms patches in mainstream large pores.
在凝析气藏的衰竭和降压过程中，凝析油的析出将单相气流转变为气液两相流，显著降低了渗透率。目前，多孔介质中凝析气相行为的微观研究主要集中在观察和描述凝析油的出现情况，缺乏对整个衰竭周期内凝析油的定量计算和直接观测。本文采用微观可视化方法模拟凝析气藏的衰竭过程。通过按特定比例混合甲烷、乙烷、己烷和癸烷制备了含油率分别为175.3和505.5 g/cm的凝析气。从真实岩心铸体薄片中提取孔隙结构，并采用化学湿法蚀刻方法制作了最小孔径为20μm、面积孔隙率为20.75%的微流控芯片。随后，进行了微流控凝析气衰竭实验，并在衰竭过程中记录芯片图像。使用ImageJ软件对衰竭图像进行灰度分析，以定量计算凝析油饱和度和采收率，分析不同凝析油含量对凝析气衰竭的影响，并比较多孔介质和PVT容器中衰竭情况的差异。得出的结论如下：多孔介质中高、低露点分别比PVT容器中的露点高3.15%和1.85%。在衰竭初期，多孔介质中的凝析油饱和度高于PVT容器中的凝析油饱和度，而在中晚期，多孔介质中的凝析油饱和度低于PVT容器中的凝析油饱和度。多孔介质中的凝析油采收率显著高于PVT容器中的衰竭采收率。凝析油倾向于在盲端和角落处析出和分散，而在主流大孔隙中容易形成斑块。
