启动压力梯度的不稳定快速测量

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。

THE FAST TRANSIENT MEASUREMENT OF THRESHOLD PRESSURE GRADIENT

Many experiments justify that there is a threshold pressure gradient (TPG) in low permeability reservoirs.The TPG of a core is usually measured by steady flow method,but the condition is very difficult to be attained,and the period to reach steady states is long.A new transient measurement of TPG is devised to measure the transient pressure of core.The detail procedures are as follow.At initial time the core is saturated by oil or water,and put the core into a sample holder with two pressure transducers at ends;Then make the core in a high pressure condition and shut in the ends of holder;After the pressure of core is steady,open one end of holder to one certain pressure,in the same time,measure the pressurd of sealed end,until attain to another balance state.In the analysis side,the percolation equation is built with effects of TPG and moving boundary.Used numerical method,the solutions are gotten,and the transient pressure curves are drawn.The TPG is solved by comparison testing pressure curve with theory curves in single log coordinate system.Finally,two samples applications show that the method is simple,fast and easy to control.