单相流煤层气井井底流压预测方法研究

Prediction of Flowing Bottomhole Pressures for Single-Phase Coalbed Methane Wells

为了准确地预测单相流煤层气井井底流压,基于流体稳定流动能量方程,建立了煤层气柱段压差和液柱段压差的数学模型.依据铁法煤田试井时地面录取的资料,预测了单相流煤层气井不同生产时间的井底流压,并将计算结果与Cullender-Smith等方法进行对比和分析.结果表明:煤层气井底流压不仅包括气柱压差,而且包括井口套压和液柱压差,预测时要考虑煤层气偏差系数和管内摩阻随管段增量变化的影响,当井深小于1000m,沉没度小于30m,产水量小于10m3/d时,预测值与实测值间的误差较小,相对误差小于1%,具有较高的精度.井底流压充分反映流体的渗流压力特征,压力平方差由0.488MPa2调整为0.891MPa2后,产气量由3270m3/d提高到6112m3/d,降低井底流压,可有效增大生产压差,利于气体解吸,提高煤层气井产能.

Based on the well liquid flow equation,an approach was proposed to predict flowing bottomhole pressure（FBHP）in single-phase coalbed methane（CBM）wells.The mathematical models of gas column and liquid column pressure drop were developed.FBHPs during the pumping production were predicted on the basis of well test data selected from Tiefa coalfield.The comparison of calculated FBHPs by Cullender-Smith and proposed method was completed.The results show that BHP results from the combined action of wellhead pressure,gas column pressure and liquid column pressure.Variation of CBM compressibility factor and friction factor with depth increments should be considered in order to predict BHPs accurately.The small errors of less than 1%between the prediction and measured values are achieved while the well depth is within 1 000m,submergence depth is within 30mand water production is within 10 m3/d.The CBM production increases from 3 270m3/d up to 6 112m3/d when pressure drops are from 0.488MPa2 to 0.891MPa2.Adjusting FBHP can effectively increase producing pressure drop,which is beneficial to gas desorption and enhance CBM production.