考虑变启动压降的低渗透气藏产能方程的建立

The Establishment of Deliverability Equation Considering Variable Threshold Pressure Drop in Low Permeability Gas Reservoir

低渗透气藏渗流中启动压力梯度的存在已经被证实并得到认可。目前低渗透气藏的产能方程,均将由启动压力梯度引起的启动压降视为一个与产量无关的常数,实践表明,现有方程在应用中存在较大误差。为此,基于低渗透气藏非达西低速稳定渗流微分方程,推导出了启动压降的表达式,分析得知启动压降并非为绝对常数,而是与测试产量有关,并以修正等时试井为例,分析了现有产能方程的误差;最后通过对启动压降进行定积分近似求解,得出了考虑变启动压降低渗透气藏的新产能方程,提出了相应的修正等时试井资料处理方法,并证明了产能试井分析新方法的实用价值。

It has been verified and accepted that there is a threshold pressure gradient （TPG） in low permeable gas reservoirs. At present, the deliverability equations for low permeable gas reservoirs were developed by assuming that TPG is constant and not related with productivity. Applications show that cur- rent equation has remarkable errors. Based on non-Darcy steady flow equation, it shows that the additional pressure drop is not a constant and is related with production rate. The error of the current deliverability equation was analyzed using modified isochronal well testing as an example. The new deliverability equa- tion was obtained through integration. The corresponding modifications for modified isochronal well testing were provided. The new deliverability equation is useful.