拟稳态扩散的煤层气井动态模型及应用

扩散对煤层气井生产动态具有非常重要的作用,为现场人员能够快速有效地对煤层气井生产动态进行预测,需要建立解析形式的动态模型。以拟稳态扩散和体积物质平衡方程为基础,建立气体扩散量与含水饱和度的关系,结合拟稳态产能方程,得到考虑煤层气体拟稳态扩散的动态预测模型。模型对煤层气井生产中后期具有较好的拟合度,通过计算,认为扩散作用在整个开发过程中对煤层气产量均有影响。扩散作用能提高煤层气峰值产量,特别是对煤层气后期产量有很重要的稳定作用。扩散系数越大,煤层气峰值越高,后期产气量越高,且稳产时间更长;扩散对累积产水影响较小;煤层气开发后期,扩散作用越强烈,储层压力下降越平缓,煤层气稳产时间越长。

Dynamic model of coal-bed methane well under pseudo-steady diffusion and its application

Diffusion plays a very important role in the dynamic production of coalbed methane(CBM)well.An analytical calculation model is required to predict the dynamic production of CBM well for the operators in production field.In order to establish the dynamic model，the pseudo-steady diffusion model，the volume material balance equation，and the pseudo-steady production equation were combined.The relationship between the gas diffusion and the water saturation was obtained.The model has a better fitting degree at the late period of production.CBM production is affected by the diffusion during the whole development process.The diffusion can improve the maximum gas production，especially，it is important for the production stability at latter stage.The maximum production，the stable production period and production volume in late stages increase with the increase of diffusion coefficient，which impacts less on water production in CBM wells.The diffusion effect determines the drawdown of reservoir pressure and the duration of stable production stages in developed CBM reservoirs.