气液非混相驱替过程中的卡断机理及模拟研究

研究气液非混相驱替过程中的相界面卡断机理及其影响因素在气驱, 气水交替及泡沫驱等提高油气采收率领域具有重要意义. 本文在原始伪势格子玻尔兹曼模型的基础上, 改进流体-流体作用力格式, 添加流-固作用力, 耦合RK状态方程, 并采用精确差分方法将外力添加到LBM框架中. 通过校准模型的热力学一致性以及模拟测试界面张力, 静态平衡接触角及液相在角隅的滞留等一系列两相体系验证模型的准确性. 基于改进的伪势格子玻尔兹曼模型, 在孔-喉-孔系统中开展气液非混相驱替模拟, 结果表明: 卡断现象与驱替压差, 孔喉长度比及孔喉宽度比有关, 只有当驱替压差处于一定范围内时, 气液两相驱替过程中才会发生卡断现象; 当驱替压差大于临界驱替压差上限时, 即使达到了经典静态准则所预测的卡断条件, 卡断也会被抑制; 当驱替压差小于临界驱替压差下限时, 无法克服毛管“钉扎”作用, 形成无效驱替. 对于固定孔喉宽度比的孔-喉-孔结构, 随着孔喉长度比的增大, 发生卡断现象的驱替压差范围增大; 对于固定孔喉长度比的孔-喉-孔结构, 随着孔喉宽度比的减小, 发生卡断现象的驱替压差范围增大. 

STUDY ON SNAP-OFF MECHANISM AND SIMULATION DURING GAS-LIQUID IMMISCIBLE DISPLACEMENT

Studying the mechanism of phase interface snap-off during gas liquid immiscible displacement and its influencing factors have great significance in the field of enhanced oil and gas recovery such as gas driving, gas water alternation and foam driving. In this work, based on the original pseudopotential lattice Boltzmann model, we improved the fluid-fluid force scheme, added the fluid-solid force, coupled the Redlich-Kwong (RK) equation of state, and used the exact difference method (EDM) to add the external forces to the LBM framework. As well as verified the accuracy of the model by calibrating the thermodynamic consistency of the model and simulating a series of two phase systems such as testing the interfacial tension, static equilibrium contact angle and retention of the liquid phase at the corner. Based on the modified pseudopotential lattice Boltzmann model, we have carried out gas-liquid immiscible displacement simulations in a pore-throat-pore system, and the results have shown that: the snap-off phenomenon is related to the displacement pressure difference, pore-throat length ratio and pore-throat width ratio, and the snap-off phenomenon occurs only when the displacement pressure difference is within a certain range. When the displacement pressure difference is larger than the upper limit of the critical displacement pressure difference, the snap-off will be inhibited even if the snap-off condition predicted by the classical static rule has been reached; When the displacement pressure difference is less than the lower limit of the critical displacement pressure difference, it cannot overcome the "pinning" effect of the capillary tube and results in ineffective displacement. For the pore-throat structure with constant pore-throat width ratio, the displacement pressure difference range in which the snap-off phenomenon occurs increases as the pore-throat length ratio increases; For the pore-throat structure with constant pore-throat length ratio, the displacement pressure difference range in which the snap-off phenomenon occurs increases as the pore-throat width ratio decreases.