利用核磁共振评价致密砂岩储层孔径分布的改进方法

岩心核磁共振(NMR)的T2分布可反映致密砂岩岩样全部孔隙信息,毛细管压力曲线只能反映一部分孔隙信息。提出改进方法,通过对长庆油田致密砂岩储层24块岩样核磁共振T2分布和毛细管压力曲线分析,消除致密砂岩储层微孔隙对T2分布贡献后,研究剩余T2分布与毛细管压力曲线之间的关系,得到了转化系数比较准确的经验公式。核磁共振T2分布得到的伪毛细管压力曲线的改进方法可完整反映致密砂岩的孔隙结构。实例验证表明,该方法能明显提高致密砂岩储层毛细管压力曲线的构造精度。

An Improved Method to Evaluate Pore Size Distribution of Tight Sandstone Reservoir Using NMR

Nuclear magnetic resonance(NMR) T2 distribution of core and capillary pressure can be used to characterize pore throat structures of rock in some degree,and core space reflected by NMR T2 distribution is more than that reflected by capillary pressure curves.Determining the transferring coefficient between T2 and pc is the key step when NMR is utilized to study rock pore throat structure.A new method for constructing pore structure from NMR T2 distribution is put forward,and experiential expression is derived.The method uses T2 distribution to construct capillary pressure curves after eliminating some contributions to T2 distribution.Applying the method to 24 cores from Changqing oilfield we did some analysis and comparison.It is believed that the pseudo capillary pressure curves come from NMR T2 distribution can reflect pore throat structure of tight sandstone reservoir completely.Practical tests indicate that the method can provide reliable principle and methodology support for using T2 distribution to evaluate pore structure.