凝析气藏循环注气开发注入干气超覆数值模拟

Numerical simulation on dry gas overlap in cycling gas injection development of condensate gas reservoirs

关键词:  凝析气藏  气体运移  对流扩散  注入干气超覆  数值模拟

Key words:  condensate gas reservoir  gas migration  convection diffusion  injection dry gas overlap  numerical simulation

摘要:

针对注入干气超覆现象影响凝析气藏循环注气开发效果并增加生产成本的现象，研究凝析气藏注入干气的超覆规律，基于对流扩散理论建立凝析气藏注入干气运移的数学模型，并应用该模型研究储层渗透率、储层厚度和注采压力比对注入干气超覆的影响。结果表明：随着干气注入量增加，注入干气与凝析气过渡带的宽度逐渐增加，过渡带中气体物质的量分数分布呈现中间密、两头疏的形状；运动方程中忽略重力项，干气垂向速度低而不易发生超覆；注入干气超覆强度随着储层渗透率增加而降低，减少储层开采厚度和提升注采压力比可明显降低注入干气超覆。

Abstract:

The overlap phenomenon of injected dry gas discovered in recent years has influenced the development effect of gas injection in condensate gas reservoirs, and therefore increased the production cost. In order to study the migration rule of dry gases in condensate gas reservoirs, based on the theory of convection diffusion, a mathematical model of dry gas migration in condensate gas reservoirs was established. The effects of reservoir permeability, reservoir thickness and injection production pressure ratio on the injection dry gas overlap were studied by using this model. The results show that the width of the transition zone between dry gases and condensate gases increases gradually with the increase of the amount of dry gas injection, and the distribution of dry gas mole fraction in the transition zone presents the shape which is dense in the middle and sparse at two heads. The gravity term is ignored in the motion equation, and the dry gases are not easy to overlap as their vertical velocities are low. The overlap strength of the injected dry gases decreases with the increase of the permeability of the reservoir. Decreasing the reservoir thickness and increasing the pressure ratio of injection and production can significantly reduce the overlap of the injected dry gases.