考虑启动压力梯度的低渗透气藏压裂井产能分析

低渗透气藏中的多数井自然产能都很低,需要进行压裂改造后才具有生产能力。同时,气体在该类气藏中的渗流一般为存在启动压力梯度影响的非达西渗流。为此,根据保角变换原理,将带垂直裂缝的气井渗流问题,转化为易于求解的单向渗流问题;然后基于Forchheimer二项式渗流方程,考虑低渗透气藏中启动压力梯度存在的影响,推导得到了低渗透气藏中垂直裂缝井的产能计算公式;在此基础上,绘制分析了理论产能曲线,并用现场实例进行了验证。结果表明:启动压力梯度会影响低渗透气藏压裂井产能,压裂气井的产量随着启动压力梯度的增加而降低。该方法简单实用,便于现场应用。

Productivity analysis of a fractured well in low-permeability gas reservoirs considering threshold pressure gradient

The natural productivity is low for most wells in the low permeability gas reservoirs, which need to be stimulated by fracturing to regain production capacity. Meanwhile, the gas flow in such reservoirs is non Darcy flow influenced by the threshold pressure gradient. According to the conformal transformation principle, the problem of hydraulically fractured gas well flow is converted into the one way flow problem which is easier to solve. Based on the Forchheimer binomial flow equation, with the influence of the threshold pressure gradient in the low permeability gas reservoirs taken into account, the computation formula for the productivity is deduced for the hydraulically fractured wells. Moreover, the theoretical production curve is drawn and analyzed, and then is further validated with field cases. The results show that the threshold pressure gradient does have influence on the production capacity of the hydraulically fractured wells in the low permeability reservoirs. The production of the fractured gas wells decreases with the increase of the threshold pressure gradient. This method is simple and can be easily put into practice.