低渗欠饱和煤层气井产能分析新方法研究

Study on novel method of production capacity analysis on low permeability and unsaturated coalbed methane well

为准确获取煤层气井物理性能参数,提出了一种简便的基于生产初期排水数据的产能分析新方法,首先,考虑煤层普遍具有的低渗特征,引入调查半径公式,计算各个时刻煤层气井压力波前缘位置,然后,基于连续稳态方法,推导各个时刻考虑应力敏感与压力波扩展的稳态渗流方程;最后,对渗流方程进行线性化处理,得到适用于低渗欠饱和煤层气井的产能分析新方法,该方法的可靠性与应用性通过与数值模拟以及现场实例对比进行研究。研究结果表明:新方法预测的渗透率与实际渗透率间的误差为2.38%,表皮因子的误差为6.59%,满足现场工程应用需求,新方法能够准确获取储层物性参数,为气井后期产能预测,生产制度调整提供有效理论依据。

In order to accurately have the physical performance parameters of the coalbeds methane well,based on the water drainage data at the initial production period,a new method of a easy production capacity analysis was provided.Firstly in consideration of the low permeability features of the seam generally,an investigation radius formula was introduced to calculate s front edge position of the pressure wave in the coal bed methane at each time.Secondly based on the continuous steady state method,the stress sensitivity considered at each time and the steady-state seepage equation of the pressure wave expansion was derived.Finally,a linear treatment was conducted on the seepage equation and a new method of the production capacity analysis suitable to the low permeability and unsaturated coal bed methane well was obtained.A study was conducted on the reliability and application of the method with the numerical simulation and site case comparison.The study results showed that the error between the permeability predicted with the new method and the actual permeability was 2.38% and the error of the epidermal factor was 6.59%.All those errors could meet the requirements of the site engineering application.The new method could accurately obtain the reservoir physical parameters and could provide the effective theoretical basis to the late production prediction of the gas well and the adjustment of the production system.