Distribution characteristics of movable fluid in tight sandstone based on nuclear magnetic resonance

Movable fluid parameter is an important index to evaluate the seepage characteristics of tight sandstone reservoir. Combined with high-pressure displacement and nuclear magnetic resonance movable fluid testing principle, the nuclear magnetic resonance movable fluid characteristics of six typical tight sandstone core samples of Xujiahe Formation in Central Sichuan Basin were studied. Based on mercury injection capillary pressure curve, the nuclear magnetic resonance T2 spectrum distribution was converted into pore throat According to the radius distribution, the minimum pore throat radius of the movable fluid and the contribution of different pore sizes to the movable fluid are determined. The research shows that the movable fluid saturation of the tight sandstone reservoir in the second member of Xujiahe Formation in Central Sichuan is closely related to the pressure difference, with good logarithmic correlation, and the main contribution to the movable fluid saturation is the reservoir space > 0.1 μm. 70% of the total movable fluid saturation is injected at a lower pressure (about 5MPa). In the later stage, high pressure injection can only enter the reservoir pore with small pore size, and the total amount is small and increases slowly. Therefore, the total contribution of high pressure drive to gas saturation in the later stage is small.