注气驱替煤层气数值模拟

建立一种注气驱替煤层气的双重介质数学模型,考虑注气驱替煤层气中多组分气体渗流、吸附/解吸、扩散及孔隙度和渗透率敏感性等多物理场的耦合,用有限差分方法对数学模型数值求解,并验证模型的有效性.通过实例模拟,对比分析注入CO₂、N₂和70%N₂+30%CO₂提高采收率、产出组分动态及储层物性.计算表明:注入CO₂、N₂及其混合气体均能显著提高煤层气藏采收率,提高程度可达28%以上;N₂在注入后迅速突破产出,而CO₂突破时间较晚;注气后基质的收缩/膨胀效应在孔隙度和渗透率敏感性中起主导作用,CO₂吸附造成孔隙度和渗透率减小,而N₂吸附将增大孔隙度和渗透率.

Numerical Simulation of Coalbed Methane Displacement with Gas Injection

A double medium mathematical model for coalbed methane displacement with gas injection is established. Multi-physics coupling process containing Darcy flow,adsorption/desorption and diffusion of multiple component gas and variation of porosity and permeability is involved. The model is solved numerically with finite difference method and validity of the model is verified. In example simulation calculations,improved recovery,evolution of produced gas composition and variation of coal seam properties under injection of CO₂、N₂and 70% N₂+ 30% CO₂ are contrastively analyzed. It indicates that injections of CO₂、N₂and their mixed gas are able to improve coalbed methane recovery significantly by a degree over 28 %. N₂ breaks through rapidly after injected,while CO₂ occurs in production well later. Shrinkage /swell effect plays a dominant role in variation of porosity and permeability after gas injection.Adsorption of CO₂ reduces porosity and permeability,while adsorption of N₂ leads their increase.