低渗透砂岩渗流启动压力梯度

为了研究低渗透砂岩的启动压力梯度,设计了一种非稳态渗流中测量压力的试验方法。岩心中形成稳定渗流后,关闭驱替泵,测量岩心封闭端的压力衰减曲线。建立了考虑启动压力梯度影响的一维低渗透岩心中液体不稳定渗流的数学模型。用数值有限差分的方法进行求解。封闭端压力衰减曲线的试验结果和理论计算结果吻合较好,从而验证了试验方法和数值模型的可靠性。试验结果表明,启动压力梯度与岩心的气测渗透率之间并不存在负相关的关系;同一块岩心在初始稳定渗流速度大的情况下,岩心的启动压力梯度小。这与产生启动压力梯度的机理的边界层理论解释相符合。

Threshold pressure gradient of low permeability sandstone

The threshold pressure gradient of low permeability sandstone was studied experimentally by measuring the pressure attenuation in an unsteady seepage flow. After establishing a steady flow in the rock core, the pump was stopped, the pressure decrease at the closed end of the rock core was recorded. A numerical model was also developed to simulate the process including the effect of the threshold pressure gradient. The numerical results agree well with the experimental data. The experimental results show that the threshold pressure gradient has not a negative corelation with the air permeability of the rock. The same rock core has a lower threshold pressure gradient when larger steady threshold seepage velocities occur. This result agrees with "boundary layer" theory that explains the threshold pressure gradient mechanism.