基于T2截止值确定致密岩心表面弛豫率

确定致密岩心样品表面弛豫率的最常用方法是平均值法和比表面积法，但平均值法结合了压汞测试，会对岩心造成永久伤害。提出了一种基于T₂截止值确定致密岩心表面弛豫率的无损新方法。首先，使用该方法确定岩心样品表面弛豫率；之后，将计算结果与平均值法和比表面积法进行对比，并通过选择合适的表面弛豫率将核磁共振T₂谱转化为孔隙直径分布；最后，获取样品残余油分布。结果表明，四块岩心样品最终表面弛豫率分别为5.85，2.98，4.66，2.17 μm/s；结合三种方法计算结果可获取中孔和大孔的孔隙直径分布；残余油主要分布在微孔和中孔。该方法是一种无损测试方法，有助于快速有效确定致密岩心表面弛豫率。 

Determination of surface relaxivity for tight sandstone cores based on T2 cut-off value

The surface relaxivity for tight cores is commonly determined by the methods of average pore radius (ARS) or surface-to-volume ratio (SVR). The ARS method is time-consuming, and permanent damage to core samples will occur due to the injection of mercury. In this study, a non-destructive method is proposed, instead of the ARS method, to calculate the surface relaxivity of tight core samples based on T₂ cut-off value. Firstly, surface relaxivity is calculated using the new method (pseudo T₂ cut-off, PTC). Secondly, the calculated surface relaxivity of ARS and SVR methods are compared. Thirdly, the T₂ spectrum is converted into pore diameter distribution by choosing appropriate surface relaxivity. Finally, residual oil distribution can be obtained. The ultimate surface relaxivity values for tight sandstone core samples are 5.85, 2.98, 4.66, and 2.17 μm/s. Moreover, we obtained the pore diameter distribution in mesopores and macropores by jointly using these three methods. Residual oil is mainly distributed in micropores and mesopores. The new method proposed in this study is nondestructive and is helpful to quickly and efficiently determine the surface relaxivity of tight cores.