低渗透致密储层气体低速非达西渗流地层压力分布及产能分析

Analysis of formation pressure distribution and productivity of low permeability tight gas reservoirs with low-velocity non-Darcy flow

低渗致密储层中含水条件下气体流动呈现低速非达西渗流特征。基于此认识,建立了低渗致密储层气体低速非达西渗流压力特征方程,推导了定压力边界和定产量边界条件下的径向流解析解,给出了低速非达西渗流条件下产能公式。计算分析表明:低渗致密储层气体低速非达西流动不同于有激励即有响应的达西流动,低速非达西流动必须克服启动压力梯度后才能流动;低渗致密储层气体低速非达西流动时,近井地带能量递减远快于达西流动的情况,储层波及范围小,存在合理的动用半径;给定不同配产情况下,可以确定井筒压力以及对应的有效动用半径;在给定压力条件下,不同的渗透率和气藏储量丰度对应不同的气井产能。

The gas flow in low permeability tight water-bearing reservoirs exhibits the characteristics of low velocity non-Darcy flow.Based on this understanding,a pressure characteristic equation for low velocity non-Darcy gas flow in low permeability tight reservoirs was established,analytical solutions for radial flows under constant pressure boundary and constant production boundary conditions were derived and a productivity formula was given for the low velocity non-Darcy flow.The calculation study indicated that the low velocity non-Darcy flow in low permeability tight reservoirs was different from the Darcy flow with stimulations,i.e.responses and it had to overcome the kickoff pressure gradient to flow.When the gas in low permeability tight reservoirs flowed at low velocity in non-Darcy manner,the energy near the wellbore region declined much faster than that in Darcy manner,leading to smaller swept area and reasonable producing radius.Given different production quotas,wellbore pressure and corresponding effective producing radius could be determined.Under given pressure conditions,different permeability and reserves abundance of gas reservoirs corresponded to different productivity of gas wells.