试验表明 ,低渗透油藏存在启动压力梯度。以往采用稳态渗流法测量岩心的启动压力梯度 ,但效果不好。针对低渗透岩心稳定时间长 ,流量精确测量困难的问题 ,设计了一种用非稳态渗流测压方式求解岩心的启动压力梯度的方法。设计实验方法为 :初始时刻 ,将岩心在高压下饱和原油 ,在一端封闭 ,并装入测压计 ,待系统压力平衡且稳定后 ,将岩心另一端放空至某一压力值 ,连续测量封闭端压力变化 ,直至系统达到稳定状态。理论方面 ,考虑启动压力梯度和动边界的影响 ,建立低渗透岩心中液体的不稳定渗流方程 ,并用数值有限差分的方法求解 ,得到岩心封闭端的不稳定无量纲压力曲线。在双对数坐标图上 ,用实测压力数据和理论无量纲压力曲线拟合 ,求出低渗透岩心的启动压力梯度。此方法的优点是实验简单 ,实验条件易于控制 ,实验时间短 Experiments show that there is a starting pressure gradient in low permeability reservoirs. In the past, steady-state seepage method was used to measure the start-up pressure gradient of core, but the effect was not good. Aiming at the problem that the stability of low-permeability core is long and the flow measurement is difficult to measure accurately, a method of solving the start-up pressure gradient of core with unsteady seepage pressure manometry is proposed. The experimental design method is as follows: At the initial moment, the core is saturated with crude oil under high pressure, closed at one end, and loaded into the manometer. After the system pressure is balanced and stabilized, the other end of the core is vented to a certain pressure value, Pressure changes until the system reaches a steady state. In theory, considering the effect of starting pressure gradient and moving boundary, the unsteady seepage equation of liquid in low permeability core is established and solved by numerical finite difference method, and the unstable non-dimensional pressure curve at the closed end of core is obtained. On double logarithmic plot, the starting pressure gradient of low permeability core was obtained by fitting measured pressure data and theoretical dimensionless pressure curve. The advantage of this method is that the experiment is simple, the experimental conditions are easy to control and the experiment time is short