煤层气井两相流阶段排采制度实时优化

Real-time optimization of drainage schedule for coalbed methane wells at gas-water two-phase flow stage

煤层气井气水两相流动阶段的合理排采制度的确定极为复杂,但对于煤层气井高效排采具有重要意义。考虑低渗透煤层的启动压力梯度和应力敏感性特征,根据煤层压裂后流体渗流规律的变化,基于气藏工程和稳定渗流理论,建立了煤层气藏垂直裂缝井气水两相产能方程,结合煤层气藏物质平衡方程及煤层气井产量数据,可得到煤层气井实时的采气指数曲线,根据最大产气指数原则即可实时确定最佳生产压差,从而建立了一套煤层气垂直压裂井气水两相流动阶段的排采制度实时优化方法。通过现场典型井的应用,验证了所建立的煤层气井排采制度实时优化方法的可靠性。

At the gas-water two-phase flow stage,the determination of drainage schedule is an important and complicated process. If the production pressure drop is too small,it's difficult to achieve a high production rate because of insufficient flow power. On the other hand,the excessive increase of the production pressure drop may cause an early production decline because of permeability loss around wellbore. Based on the gas reservoir engineering theory,the real-time optimization method of drainage schedule at the gas-water two phase flow stage was developed for vertically fractured coalbed methane wells. Firstly,the productivity equation for the coalbed methane vertically fractured wells at gas-water two-phase flow stage was derived with the consideration of stress sensitivity and start up pressure gradient. Using the material balance method with the combination of the cumulative gas and water rate at some time,the average pressure and fluid saturation of that moment can be calculated,then by solving the productivity equation,the real-time gas productivity index curve of coalbed methane wells can be obtained. On the basis of the principle of maximal gas productivity index,the real-time best production pressure can be determined. The case study demonstrates that the proposed real-time optimization method of drainage schedule is valid and reliable.