Distinguishing Rock Fracture and Pore's T2 Signals From NMR Experiments With Assisted X-Ray CT Imaging

Abstract

Nuclear magnetic resonance (NMR) is widely used to characterize fluids in rock pore spaces, but traditional methods have difficulty distinguishing fractures from matrix pores in complex carbonate formations. To address this, we developed a calibration method that integrates X-ray computed tomography (CT) imaging with NMR to identify fracture-related T₂ signals. The method quantitatively calibrates NMR T₂ spectra to fracture aperture sizes, improving the accuracy of fracture characterization. Fully saturated fractured samples were used, and fracture fluids were progressively removed using gas displacement techniques. NMR spectra were recorded before and after fluid removal to isolate fracture-specific signals. Fracture size distributions were estimated from CT images by pixel counting, and porosity was determined by fluid saturation measurements, with corrections for matrix porosity not captured by CT resolution. This workflow extracts fracture distributions from T₂ spectra and establishes a correlation between pore radius (r) and T₂, enabling subsequent applications in core analysis and NMR logging. The method improves differentiation between fractures and matrix pores, enhances the interpretation of NMR data, and can be adapted to heterogeneous reservoir systems.