考虑启动压力梯度的相对渗透率计算

低渗透油气层由于存在启动压力梯度，渗流规律不符合达西定律，而现今实验室处理相对渗透率曲线的JBN方法是建立在达西定律基础上的，没有考虑启动压力梯度的影响。为解决非稳态实验中对低渗透岩心的数据处理问题，在低渗透非达西渗流理论的基础上，推导了考虑启动压力梯度的油水相对渗透率计算公式，当启动压力梯度为零时，该公式与JBN计算公式相同，可以看作是JBN方法的推广。与JBN方法相比，考虑启动压力梯度后得出的油、水相对渗透率都是偏小，可以看出JBN公式对低渗透储层并不适用。考虑了启动压力梯度的影响后，得出的相对渗透率曲线更符合低渗透岩心的真实驱替过程，所以更有利于油气藏工程中的计算。

A METHOD FOR RELATIVE PERMEABILITY CALCULATION CONSIDERING START-UP PRESSURE GRADIENT

The flow in low perm reservoirs does not observe the Darcy's Law, which is contradictory to the fact that the JBN method presently used for relative permeability curve correction is based on the Darcy's Law without consideration of start up pressure gradient effect. For data correction of low perm cores in unsteady state experiment, the paper came up with a formula to calculate oil/water relative permeability considering start up pressure gradient based on the non Darcy's Law. When the start up pressure gradient was zero, it would be the same with the JBN equation; and while there was start up pressure gradient, the calculation results by the new method were smaller than those by the JBN method, showing the inappropriateness of the JBN equation for permeability calculation of low perm reservoirs. If taken into consideration start up pressure gradient, the acquired relative low perm curves would reflect well the actual displacing process of low perm core samples so as to be useful for the calculation in oil and gas engineering.