Changing the resonant nucleus by altering the static field, compensation of γ and B 0 effects in T 2 and T 2 measurements of porous media

• Published in: Journal of magnetic resonance (1997) 2024-12, Vol.369, p.107811
• Main Authors: Rajeev, Rheya, Ansaribaranghar, Naser, Aguilera, Andrés Ramírez, Marica, Florea, de Zerón, Laura Romero, Balcom, Bruce J
• Format: Article
• Language: English
• ISSN: 1096-0856

Multinuclear H, C, and Na magnetic resonance (MR) has many advantages for studying porous media systems containing hydrocarbons and brine. In recent work, we have explored changing the nucleus measured, keeping the Larmor frequency constant, by changing the static magnetic field B . Increasing the static B field distorts the field in the pore space due to susceptibility mismatch between the matrix and pore fluid. Distortion of the magnetic field in the pore space scales with the applied static field. The gradients that result from the spatial variation of the distorted field will also scale with B . The equations that describe the inhomogeneous broadening in T * show that the MR result depends on γB . The diffusion through internal field gradients effect on T depends on the product of γ and G, with G depending on B . Increasing the static field to bring a nucleus with lower γ into resonance at the same frequency will result in the products γB and γG being constant, and therefore, inhomogeneous broadening and diffusion attenuation effects in porous media are predicted to be constant. We explore the T * hypothesis with Na and H measurements of brine in porous reservoir core plugs. We explore the diffusion through internal field gradients effect hypothesis with H and C measurements of decane saturated glass beads. The nuclei chosen for study: H, C, and Na are the three most important nuclei for studies of fluids (brine and hydrocarbons) in reservoir core plugs. These three nuclei have a common resonance frequency of 33.7 MHz at static fields of 0.79 T, 3.19 T, and 2.99 T, respectively. All three fields are readily achieved with our variable field superconducting magnet.