气水两相煤层气井井底流压预测方法

基于井筒流体稳定流动能量方程，建立了煤层气柱段压差和两相液柱压差的数学模型，给出了气水两相煤层气井底流压的预测方法，并分析了各排采参数间的相互关系及其对产能的影响。研究结果表明，该算法较为准确地预测了煤层气井进入稳定排采后的井底流压；井底流压是井口套压、气柱和液柱压力综合作用的结果，能充分反映产气量的渗流压力特征；该模型充分考虑了井筒中压力增量随井深增量的变化关系，在两相液柱段每等份长度不超过25 m时，井底流压预测结果的相对误差可控制在5%以内；调整井底压力，可有效增大生产压差，控制排液量，利于煤层气体的解吸，从而提高产气量；产水量较大，动液面较高时，宜加大排液量，降低井底压力，而动液面较低时，宜放开套压。

Prediction of flowing bottomhole pressures for two-phase coalbed methane wells

Flowing bottomhole pressure (FBHP) in the coalbed methane (CBM) wells is the key parameter of determining the deliverability of coalfields. Periodic calculation and supervision of bottomhole pressures (BHP) can predict future reservoir behavior and help to adjust the working system.The mathematical models of gas column pressure and two-phase liquid column pressure were developed based on the CBM well liquid flow equation.The prediction of FBHP was given out for two-phase CBM wells.And the relationship among operational parameters and their effects on deliverability were analyzed on the basis of results.The results show that the proposed algorithm provides accurate prediction for FBHP in CBM wells.BHP results from the combined action of wellhead pressure,gas column pressure and two-phase fluid column pressure.And BHP can fully reflect percolation characteristics of CBM production.BHP is a function of depth of each column segment,and the small errors of less than 5% are achieved while each segment is within 25m.Adjusting BHP during the production can effectively increase producing pressure drop and control water flow rate,which is beneficial to gas desorption and enhance CBM production.BHP can be decreased due to increasing water displacement while dynamic fluid level is high and decreasing well head pressure while it is relatively low.