Physics Department Seminar Series-FR

Event date(s): November 23, 2023
Time(s): 01:15 PM - 02:15 PM
Category: Fredericton
Location: Fredericton

Magnetic Resonance Relaxation of Water in Porous Media, Temperature Effect

Presented by Peiyuan Yan

Nov. 23,1:15 to 2:15 p.m.
Toole Hall Room 3

Surface relaxation at the fluid-solid interface in porous media is dominated by paramagnetic relaxation and hydrogen-hydrogen dipole coupling, in paramagnetic and diamagnetic materials, respectively. My current research has focused on temperature-induced changes in surface relaxation associated with paramagnetic impurities. This neglects the potential contribution of diamagnetic surface relaxation, which may be important in diamagnetic samples. We will discuss these two limits and propose a new hypothesis regarding the temperature-dependent changes in T2 applicable to diamagnetic porous media. 

In sandstones where T2 decreases with sample temperature, we emphasize the paramagnetic relaxation mechanism, utilizing well established BT theory to explain this phenomenon. With increasing temperature, a greater number of water molecules diffuse to and interact with paramagnetic ions, thereby enhancing surface relaxation and reducing the T2 lifetime. This temperature trend, along with BT theory, has allowed us to determine pore size and pore size distribution in certain classes of porous media. 

However, in other porous media, T2 increases with temperature. In such systems, hydrogen-hydrogen dipole-dipole coupling on the surface we believe is the predominant mechanism governing surface relaxation. The correlation time of hydrogen spins residing on the surface decreases with increasing temperature, thereby increasing the T2 time. This is a common behavior observed in many samples. This presentation will outline our experimental plans to validate and support these ideas.

Building: Toole Hall

Room Number: 3