基于T_2截止值的幂函数构建毛管压力曲线

岩心核磁共振(NMR)T_2谱和毛管压力曲线都在一定程度上反映了岩石孔隙结构,理论分析表明可利用T_2谱构建毛管压力曲线,由此快速获取储层孔隙结构的信息.本文对18块岩样T_2分布和毛管压力曲线进行了分析,提出将T_2截止值作为幂函数的分段点,采用分段幂函数方法构建岩样的NMR毛管压力曲线,并与采用不分段幂函数方法获得的毛管压力曲线进行了对比.研究结果表明,与不分段幂函数方法相比,分段幂函数方法得到的结果和压汞实验测定的毛管压力曲线吻合度更高,平均拟合度(R2)达到0.9431,并且论证了T_2截止值作为分段点进行分段幂函数法构建NMR毛管压力曲线的合理性和可靠性.T_2截止值的引入提高了幂函数法构建NMR毛管压力曲线的精度,是利用NMR T_2谱构建岩样毛管压力曲线的有价值探索.

Construct NMR Capillary Pressure Curves by Piecewise Power Function Based on T2 Cutoff Values

To some extent, pore throat structures of the rock can be characterized by NMR T₂ distribution and capillary pressure curve. Theoretical analysis showed that NMR T₂ distribution of a rock could potentially be used to derive its capillary pressure curve, providing a quick and non-destructive way to obtain the pore structure distribution data of the reservoir. In this study, the capillary pressure curves of typical cores were constructed from nuclear magnetic resonance (NMR) T₂ distributions using a piecewise power function method. T₂ cutoff values were introduced as piecewise points for the power function. Then the capillary pressure curves constructed with the piecewise power function method and those constructed with the non-piecewise power function method were compared. The results showed that the proposed method had improved precision, with an averaged fitting degree of 0.943 1. Introducing of T₂ cutoff values was proven to be useful in constructing NMR capillary curves by the piecewise power function method.