确定煤层气井合理生产压差的新思路

A new discussion on the determination methods of reasonable drawdown pressure for a coalbed methane gas well

生产压差是煤层气井能够正常排采的关键,影响煤层的渗透率,进而影响了产气量。目前绝大多数的井底流压计算模型和方法都只适用于常规的油气井,在煤层气井应用上存在局限性。为此,在分析煤层气井生产压差影响因素的基础上,提出了确定煤层气井合理生产压差的两种方法——产能方程法和修正公式法,分别根据煤层气井不同阶段的产能方程和煤层气藏井底流压修正后的计算公式确定煤层气井的生产压差,并在柳林地区FL-EP3井进行了实例分析。结果表明,修正公式法用来确定煤层气合理生产压差效果较好,与实际生产数据相比,使用确定的简化和修正后的煤层气藏井底流压计算公式所得出的生产压差数据误差在4%以内,为煤层气井合理生产压差的确定和正常排采提供了技术支撑。

Drawdown pressure plays a key role in the normal production of a coalbed methane(CBM) gas well,which influences not only the permeability of a coal bed but the gas production of the well.However,current models and methods for the calculation of bottomhole flow pressure are only suitable for regular oil or gas wells but not for the CBM wells.Aiming at this,based on an analysis of the influencing factors,two methods are proposed for determining the drawdown pressure in a CBM well,namely the deliverability equation method and the modified formula method.The drawdown pressure is determined according to either the deliverability equation of different stages or the modified formula of calculating the bottomhole flow pressure.A real case study was carried out on the well Liulin FL-EP3,the experience of which shows that the modified formula method has a better performance on determining the reasonable drawdown pressure,and the calculated result,in comparison with the practical production data,is within an error of 4%.This modified formula method provides technical support for the determination of reasonable drawdown and the normal production of a CBM well.