CHARACTERISTIC OF PORE STRUCTURE AND FLOW PROPERTY IN SANDSTONES BASED ON LOW FIELD NUCLEAR MAGNETIC RESONANCE

Surface relaxivity is the most significant parameter that converts transverse relaxation time into pore size in porous media. However, the value of surface relaxivity is difficult to obtain. This paper focuses on measuring surface relaxivity to evaluate permeability of two types of sandstones (loose sandstone and tight sandstone), combining the high-speed centrifugation with nuclear magnetic resonance test. The results reveal the surface relaxivities for loose sandstones (1.89-2.20 μm/s) are larger than that for tight sandstones (0.69-0.87 μm/s). The measured surface relaxivity is consistent with that from the method of monolayer water adsorption. During centrifugation, the variation of water content is analyzed, including the pore with different size categories. Based on the measured surface relaxivity, the Schlumberger doll research model is used to estimate the absolute permeability of sandstones.