一种估算砂岩核磁T_2谱新方法

根据核磁共振弛豫机制,基于三维数字岩心技术建立一种估算砂岩核磁共振横向弛豫(T_2)谱的新方法。采用过程模拟法重建砂岩三维数字岩心,通过Delaunay剖分将砂岩微观孔隙结构划分为多个四面体孔隙单元,再用几何方法和Monte Carlo方法相结合求出每个孔隙单元的表面积与体积之比(S/V),进而获得砂岩模拟的核磁T2谱。经过大量模拟试验筛选参数,减小计算误差。考虑单峰态和双峰态核磁T_2谱,模拟结果和实验结果基本吻合。该方法有助于研究粒度分布、孔隙结构等对岩石核磁共振响应的影响。

A new method of estimating NMR T2 spectrum of sandstone

Based on nuclear magnetic resonance(NMR)relaxation mechanism and three-dimensional digital core technology, a new method of estimating the spectrum of sandstone transverse relaxation time (T₂) is established. A process-based method was used to reconstruct 3D digital rock models of sandstone. Sandstone microstructures were divided into tetrahedral pore units using Delaunay tessellation. Considering the geometry and using a Monte Carlo approach, the surface-to-volume ratio (S/V) of each pore unit was calculated, and then the T₂ spectrum of sandstone could be simulated. After a large number of simulations, suitable parameters were selected in order to reduce calculation errors. Unimodal and bimodal T₂ spectrum were considered; both results agreed well with laboratory tests. This new method is helpful in studies of different NMR response effects with varying grain sizes or pore structures.