Considering the threshold pressure gradient ( TPG) phenomenon in low-permeability reservoirs. a mathematical unsteady flow model of horizontal well with TPG was established in box-shaped reservoir. The numerical solution of bottom pressure of horizontal well was obtained by using the Galerkin finite element method, which was verified by comparing with the classic Odeh solution. The results show that the horizontal well pressure and its derivative curves present an upward tendency when the TPG is considered. And the bigger the TPG, the more severe the curves upturned, namely, the greater pressure difference is required. Meanwhile , the effect of TPG on pressure derivative increases gradually , which is essentially different from the curve upturned when the pressure reaches the surrounding boundary.%针对低渗透油藏渗流普遍存在启动压力梯度的特点,建立考虑启动压力梯度的盒状油藏水平井不稳定渗流数学模型.利用伽辽金有限元方法得到水平井井底压力数值解,并与经典的Odeh解析解对比验证本数值算法的正确性.结果表明:启动压力梯度存在时,水平井压力及压力导数曲线都呈上翘趋势,且启动压力梯度越大,曲线上翘越明显,即所需压差越大;启动压力梯度对压力导数的影响是一个逐渐抬升的过程,与压力波传播到周围边界而引起的曲线上升有着本质上的不同.
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