煤层倾角对煤层气水平井产能影响的数值模拟

A numerical simulation on the impact of coal seam dip on productivity of CBM horizontal well

对于含倾角的煤层,由于重力势能的影响,不同煤层倾角下水平井表现出不同的产能规律。在考虑煤层气藏与水平井筒流动耦合的基础上,以煤田煤层实际资料为例,通过数值模拟的方法研究了不同煤层倾角下水平井生产过程中的压力和气相饱和度分布情况,并对U型水平井的后期生产方式给出了建议。模拟结果表明,水平井跟端位于煤层倾角低部位时排水效果更好,产气量更高;随着煤层倾角的增大,煤层气水平井累积产气量与产水量均减小;不同煤层倾角下,受气水重力分异的影响在生产过程中会出现气体在倾角高部位聚集的情况,且倾角越大这种现象越显著;利用U型井开采倾斜煤层时,在开发后期可使其两端同时生产,以达到顶部产气底部产水的效果,使倾角高部位聚集的气体也得到有效开采。

The effect of gravitational potential energy is not ignorable in inclined coal seam,so at different coal seam dip angles the production rates of horizontal wells are different. Considering the coupled flow of coal seam and wellbore,and selecting the geological data in a coal field,the pressure and saturation distributions were investigated at different dip angles during the production process of horizontal wells by numerical simulation. A new production mode of U-shaped horizontal well in the late period was recommended. The simulation results show that when the heel of horizontal well is located in the lower region of inclined coal seam,the dewatering and gas productivity are more effective.With the increment of dip angle,the cumulative gas and water production rates of CBM horizontal wells decrease. In inclined coal seams,gas migrates towards the higher region due to the effect of the difference in density between gas and water during the production process,and it becomes more obvious when dip angle increases. During the late production period of U-shaped well for inclined coal seam,both ends can be working together to achieve the aim of gas output from the top and water output from the bottom,so the accumulated gas in the higher region can be effectively produced.