低渗透气藏气井等时试井及一点法产能公式

Isochronal Well-testing of Gas Well in Low-Permeability Reservoirs and Productivity Formula of One-point Method

低渗气藏由于其低孔、低渗和高含水饱和度的特征,气体必须克服启动压差后才能流动,气井产能方程由二项式变为了三项式,在进行等时试井分析以及应用一点法产能公式时,需考虑启动压力梯度影响。为此,建立了附加压力损失值与开井时间关系式,提出了处理等时试井资料的合理方法,同时基于考虑启动压力影响的产能方程推导出了适合于低渗气井的一点法公式。推导显示:与常规的一点法公式相比,经验参数由1个变为了2个,并且都与启动压力梯度大小有关。最后通过实例分析证实了该方法是切实可行的。

For low-permeability gas reservoirs,characterized by low porosity,low permeability,and high water saturation,gas must avoid start-up pressure drawdown before it can flow.So,an influence of start-up pressure gradient needs to be considered when analyzing isochronal well-testing and employing productivity formula of one-point method.In this study,the relationship between loss value of additional pressure and open well time is established,and a reasonable method to process isochronal well-testing data is also proposed.Meanwhile,based on the productivity formula of which the start-up pressure influence is considered,the one-point method formula suitable for low-permeability gas well is derived.The derivation shows that(1) the number of empirical parameter changes from one to two;and(2) all parameters are related to start-up pressure gradient when com pared to conventional one-point method formula.Finally,the method is proved to be feasible through case study.