煤层气直井井筒环空压力模型

为实现煤层气直井排采各阶段井筒环空压力分布的计算,为煤层气井的控压排采提供指导。结合国内煤层气井的生产实际,研究了以油管排水、环空产气为生产方式的煤层气直井,在排采各阶段的井筒内流体分布状态。提出了环空内的纯液流仅出现于煤层气解吸产出前;气液两相流阶段的环空内仅产生泡状流与段塞流;环空内气体上升不携液。基于此,采用水动力学方法,建立了3个井筒环空压力模型,分别为环空液体单相压力模型、环空气液两相压力模型以及环空气体单相压力模型,并给出了模型间的过渡条件及模型求解步骤,从而实现煤层气直井排采各阶段的环空压力分布计算。经41口井、共71组实测数据验证,所建立的3个环空压力模型,其计算结果与实测值的平均误差依次为:2. 70%,7. 96%及3. 80%,对煤层气直井井筒环空压力的计算具有一定准确性与实用性。

Wellbore annulus pressure model of vertical coalbed methane well

In order to calculate the pressure distribution of wellbore annulus of vertical coalbed methane well in each production stage,and provide guidance for the control pressure production in coalbed methane wells,combined with the domestic production of coalbed methane,the gas liquid distribution of CBM vertical wells’wellbore at every production stages has been studied,which uses the production method of tubing drainage and annular production gas.The pure liquid flow occurs in the annulus only before the desorption of coalbed methane has been proposed.Only bubbly and slug flow occurs in the annulus at gas liquid two phase flow stage.And the gas rises in the annulus without carrying liquid.Based on this,using the hydrodynamics method,three wellbore annulus pressure models have been established.They are single phase liquid pressure model,gas liquid two phase pressure model and single phase gas pressure model respectively.Transition condition and solution steps of the model have been given.And at each production stage,the pressure distribution of wellbore annulus of vertical coalbed methane well can be calculated.Verified by a total of 71 groups of measured data,coming from 41 CBM wells,the average error of three models are 2.70%,7.96% and 3.80%.The wellbore annulus pressure model of vertical CBM well has reasonable accuracy and practicability.