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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。
The existence of starting pressure gradient in the seepage of low permeability gas reservoirs has been confirmed and recognized. At present, the productivity equation of low permeability gas reservoirs considers the starting pressure drop caused by the starting pressure gradient as a constant unrelated to the production. Practice shows that the existing equations have large errors in application. Therefore, based on the non-Darcy low-velocity steady seepage differential equation of low permeability gas reservoir, the expression of the start pressure drop is deduced. It is found that the start pressure drop is not an absolute constant, but is related to the test output, Well testing as an example, the error of the existing capacity equation is analyzed. Finally, the new integral equation of the pressure drop percolation gas reservoir considering the start-up and pressure reduction is obtained by the definite integral approximation of the start pressure drop, and the corresponding modified isochronous test Well data processing methods, and proved the practical value of the new method of productivity test analysis.