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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。
In order to study the starting pressure gradient of low permeability sandstone, a test method for measuring pressure in unsteady seepage flow was designed. After the formation of a steady flow in the core, the displacement pump is closed and the pressure decay curve at the closed end of the core is measured. The mathematical model of unsteady seepage in one-dimensional low-permeability core considering the influence of start-up pressure gradient is established. Use finite difference method to solve. The experimental results of the closed-end pressure decay curve agree well with the theoretical calculation results, which proves the reliability of the test method and the numerical model. The experimental results show that there is no negative correlation between the start-up pressure gradient and the gas permeability of the core. Under the condition of large initial steady seepage velocity, the start pressure gradient of the core is small in the same core. This is consistent with the theoretical interpretation of the boundary layer that produces the mechanism of the start-up pressure gradient.