Pore fluids are generally classified into movable fluid and irreducible fluid by one or two NMR T₂ cut-offs (T_2C). Fluid movability in tight sands may not be accurately characterized by pore size-based classification methods solely because of the complex pore structure and heterogeneity in pore size. In this study, we propose a nine-grid model to characterize fluid movability and calculate the percentages of free fluid (FF), capillary-bound fluid (CAF), and clay-bound fluid (CBF). The pore size distributions and capillarity boundaries are converted from T₂ and mercury injection capillary pressure (MICP). Three T₂ spectra (T_FF, T_CAF, and T_CBF) under water saturation, centrifugation, and heat-treatments are measured to classify pore fluids as FF, CAF, and CBF according to the pore capillary force needed to displace them. T_2C1 and T_2C2 are calculated to classify pores into three size categories. Finally, the nine-grid model that is composed of the three T₂ distributions and two T_2C is applied to explain results of a N₂ displacement test and evaluate fluid movability in two samples. The results suggest that the conventional classification method based on fixed T_2C results in the underestimation of CAF and overestimation of CBF. The macro-pores (T₂ > T_2C1) range in size larger than 85.20 nm and 113.64 nm and have pore capillary pressures lower than 6.46 MPa and 8.62 MPa. Micro-pores (T₂ < T_2C2) are smaller, ranging in size lower than 13.96 nm and 31.84 nm, and have high capillary pressures. Compared with conventional methods, the introduced model interprets the pore capacity-related displacement process well, especially for the remarkable displacement ratio of medium pores. The co-effect of fluid types and pore sizes in gas-displacing-water tests indicates that the process is primarily governed by fluid-matrix interaction and the connections among pores, rather than a simple sequential displacement of larger-to-smaller pores.

孔隙流体通常通过一个或两个 NMR T ₂临界值 ( T _2C )分为可动流体和束缚流体。仅由于复杂的孔隙结构和孔径的不均匀性，致密砂岩中的流体流动性可能无法通过基于孔径的分类方法准确表征。在这项研究中，我们提出了一个九格模型来表征流体的流动性并计算自由流体 (FF)、毛细管束缚流体 (CAF) 和粘土束缚流体 (CBF) 的百分比。孔径分布和毛细管边界由T ₂和压汞毛细管压力(MICP)转换而来。三个T ₂光谱( T _FF , T_CAF和T _CBF ) 在含水饱和度、离心和热处理条件下进行测量，以根据驱替它们所需的孔隙毛细管力将孔隙流体分为 FF、CAF 和 CBF。计算T _2C1和T _2C2以将孔隙分为三个尺寸类别。最后，应用由三个T ₂分布和两个T _2C组成的九格模型来解释N ₂位移测试的结果并评估两个样品中的流体流动性。结果表明，基于固定T _2C的常规分类方法导致对 CAF 的低估和对 CBF 的高估。大孔( T ₂  >  T _2C1 ) 的尺寸范围大于85.20 nm 和113.64 nm，孔隙毛细管压力低于6.46 MPa 和8.62 MPa。微孔（T ₂  <  T _2C2) 更小，尺寸范围低于 13.96 nm 和 31.84 nm，并且具有高毛细管压力。与常规方法相比，所引入的模型较好地解释了与孔隙容量相关的驱替过程，尤其是中孔隙的显着驱替率。气体驱替水试验中流体类型和孔径的共同作用表明，该过程主要受流体-基质相互作用和孔隙之间的连接控制，而不是由较大孔隙到较小孔隙的简单顺序置换。