Transverse relaxation processes in porous sedimentary rock

Abstract

Transverse relaxation rates of a number of water-filled porous rock samples have been measured as a function of static magnetic field strength and Carr-Purcell pulse spacing. At the lowest field and shortest pulse spacings, T 2 appears to be dominated by relaxation at the fluid-solid interface, while at higher fields and longer pulse spacings, there is clear evidence of molecular diffusion in a magnetic field gradient. This gradient is due to the magnetic susceptibility contrast between grain material and the pare fluid. Samples with small pores show the strongest evidence for restriction of diffusion, and a broad distribution of pore sizes is another important complicating factor. A theory which takes into account all the above effects in a consistent manner has been developed; the total relaxation rate is not simply the sum of the relaxation rates of the individual processes. With parameter selection guided by independent measurements of magnetic susceptibility and pore size, the theory adequately reproduces experimental results.