考虑启动压力梯度的低渗透气藏不稳定渗流特征

Unstable percolation characteristics of low permeability gas reservoirs considering starting pressure gradient

低压低渗透气藏气体渗流时普遍存在启动压力梯度,在气藏开发过程中不能忽略。在考虑气体渗流启动压力梯度的基础上,建立了不同外边界低渗透气藏不稳定渗流模型,通过模型求解和Stehfest数值反演方法获得了模型的实空间解,在此基础上实例分析了启动压力梯度对低渗透气藏不稳定渗流压力动态特征的影响。研究结果表明,启动压力梯度增加了气体渗流过程中的阻力,气井定产量生产时,考虑启动压力梯度影响时的井底压降要高于不考虑启动压力梯度时的井底压降,启动压力梯度越大,井底压力下降越快,地层能量衰竭越严重。

Starting pressure gradient exists commonly in the percolation of gases in low-permeability and low-pressure gas reservoirs,which cannot be ignored during gas reservoir development.On the basis of considering the pressure gradient of the gas seepage,unstable percolation models of various outer boundary low permeability gas reservoirs was established.The real space solution of the model is obtained through solving problems by models and Stehfest numerical inversion method.On this basis,the influence of the starting pressure gradient on the dynamic characteristics of the unstable percolation pressure in low permeability gas reservoirs is analyzed by a case study.The results of the study indicate that the starting pressure gradient increases the resistance of gas percolation.When the gas well produces ata set output,the bottomhole pressure drop under the consideration of the effect of the starting pressure gradient is higher than the bottomhole pressure drop without consideration of the starting pressure gradient.The greater the starting pressure gradient,the faster the downhole pressure drops and the more severe the formation energy diminishing.