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田键, 康毅力, 游利军, 贾钠, 王艺钧, 秦朝中. 致密砂岩孔隙尺度下气−水界面动态演化可视化实验研究. 力学学报, 2024, 56(3): 861-872. DOI: 10.6052/0459-1879-23-445
引用本文: 田键, 康毅力, 游利军, 贾钠, 王艺钧, 秦朝中. 致密砂岩孔隙尺度下气−水界面动态演化可视化实验研究. 力学学报, 2024, 56(3): 861-872. DOI: 10.6052/0459-1879-23-445
Tian Jian, Kang Yili, You Lijun, Jia Na, Wang Yijun, Qin Chaozhong. Visualization study on the evolution of gas-water interface at pore-scale in tight sandstone rocks. Chinese Journal of Theoretical and Applied Mechanics, 2024, 56(3): 861-872. DOI: 10.6052/0459-1879-23-445
Citation: Tian Jian, Kang Yili, You Lijun, Jia Na, Wang Yijun, Qin Chaozhong. Visualization study on the evolution of gas-water interface at pore-scale in tight sandstone rocks. Chinese Journal of Theoretical and Applied Mechanics, 2024, 56(3): 861-872. DOI: 10.6052/0459-1879-23-445

致密砂岩孔隙尺度下气−水界面动态演化可视化实验研究

VISUALIZATION STUDY ON THE EVOLUTION OF GAS-WATER INTERFACE AT PORE-SCALE IN TIGHT SANDSTONE ROCKS

  • 摘要: 水相圈闭是非常规天然气开发面临的主要储层损害问题之一, 采用岩心驱替实验无法直观揭示孔隙内部气−水两相分布和流动演化过程, 因此, 对水相圈闭损害微观作用机理的认识有待提高. 根据致密砂岩铸体薄片, 设计出一维通道和二维孔隙网络两种玻璃芯片模型, 可视化研究了孔隙尺度下渗吸和返排过程中气−水界面演化和两相流动行为; 结合岩心驱替实验, 探讨了孔隙尺度气−水界面演化与致密砂岩宏观气体流动的关联机制. 结果表明: (1)孔隙尺度下气−水界面随含水饱和度的增加由水膜水气−水界面向毛管水气−水界面演化, 并主要通过卡断和绕流两种形式破坏气体流动连续性; (2)优势通道既是孔隙尺度下水相返排的快速走廊, 也是气泡运移和贾敏效应发生的主要通道, 是造成储层产水但不产气的一个重要原因; (3)孔隙尺度下气−水界面演化引起的水封气现象是水相圈闭损害的具体微观作用形式, 宏观表现为岩心尺度上水相难以彻底返排和气体渗透能力不能完全恢复. 实验结果可为储层岩石孔隙尺度下水相圈闭作用机理和气水可动性分析提供理论依据.

     

    Abstract: Water phase trapping is one of the main engineering issues that restrict the efficiency of development in unconventional gas reservoirs. The damage essence of water phase trapping is the decline of gas flow capacity induced by water invasion at pore-scale. Due to the limitations that core-scale displacement experiments cannot visually reveal the evolution of gas-water interface and distribution of gas and water at pore-scale, a visualization study of gas-water two-phase flow at pore-scale using microfluidics was conducted in this study. Two types of micromodels including the single flow channel model and pore network model were designed based on analysis of the pore structures from the CT images of some real tight sandstone rocks, and related microchip models were fabricated and etched accordingly. Then the dynamic evolution of gas-water interface and flow phenomena at pore-scale were visually investigated using these two micromodels. The core-scale flow experiments were also carried out to analyze the gas and water flow mechanisms, which was used to link the pore-scale flow mechanisms. The results show that snap-off and bypass flow were the two most important pore-scale events that occurred during the evolution of gas-water interface to break the continuity of gas flow. Once the gas phase is discontinuous, the Jamin effect becomes remarkable to hinder the gas flow and water drainage, resulting in gas entrapment and residual water produced. The advantage flow path is considerable for gas and water flow at pore-scale, and can be also an unfavorable factor to harm the gas discharging water process. Combined with the core-scale analysis and pore-scale visualization, the damage mechanisms of water phase trapping in tight sandstone reservoirs is elucidated from the perspective of pore-scale evolution of gas-water interface. These findings will improve the knowledge of gas and water flow mechanisms and reveal the intrinsic mechanism of the water phase trapping in tight formations.

     

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