摘要
针对气井生产过程中存在的流固耦合作用，在充分考虑真实天然气的偏差因子、密度以及黏度随压力变化的基础上，建立数学模型，利用COMSOL Multiphysics软件对应力场、渗流场进行耦合计算，得到流固耦合作用下的渗流场分布。从中提取井底上方20 m处切线上的地层压力、孔隙度、渗透率、渗流速度、气体密度、气体黏度等数据，进一步分析耦合渗流场的分布特点。研究得出：气井耦合渗流场中压力分布与常规数值分析得到的“压力漏斗”趋势相似，但压力数值偏小；由于应力场的作用，耦合渗流场中地层的孔隙度和渗透率是变化的，尤其在井底附近的减小程度显著，进而导致耦合渗流速度小于常规渗流场，最终影响气藏的开发动态；受压力变化的影响，天然气的黏度、密度分布也近似为“漏斗”趋势。结果表明，考虑流固耦合作用下的渗流场才是地下渗流的真实反映。
Abstract
Aiming at the existence of fluid-solid coupling during gas well production, based on the sufficient consideration of the changing of real gas deviation factor, density and viscosity with pressure, a mathematic model was established. Seepage field distribution under the action of fluid-solid coupling had been gotten through the coupling calculation between stress field and seepage field with COMSOL Multiphysics software. The distribution data at 20 meters above bottom hole were extracted, including formation pressure, porosity, permeability, Darcy velocity, gas density and gas viscosity. The features of the fluid-solid coupling seepage field were further analyzed. The study leads to the ideas that the pressure distribution in gas well coupling seepage field is similar to the trend of the "pressure funnel" obtained in the conventional numerical analysis, but coupled seepage pressure values are smaller. And because of the effect of stress field, the formation porosity and permeability in coupling seepage field are variable, especially evidently decreased in the vicinity of bottom hole, which cause that the coupled Darcy velocity is less than that of conventional seepage field and affect the development of gas pool at last. The distribution trends of gas viscosity and density are similar to the trend of "funnel" because of the effect of pressure change. The study shows that the seepage field considering the effect of fluid-solid coupling is a true reflection of underground seepage.
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