Ground-Truth Validation of T2 Estimates From Steady-State Surface NMR

Abstract

Steady-state sequences are a new protocol for surface nuclear magnetic resonance (NMR), that can yield high quality data in a short time. In addition to faster acquisition, steady-state surface NMR purports to measure the transverse relaxation time $T_2$, which is correlated with hydrogeological parameters like pore-size. This is in contrast to the effective transverse relaxation time $T_2^{\ast }$ associated with standard single pulse measurements, which may or may not be correlated with pore-size. While previous studies suggest that steady-state measurements have enhanced sensitivity to $T_2$, a ground-truth validation has not yet been done. We compare steady-state surface NMR results against borehole NMR logs at four locations. For relaxation regimes of $T_2$ > 10 ms, $T_2$ profiles from steady-state data are in excellent agreement with borehole measurements, provided the assumption of homogeneous horizontal layers is valid. Even in more complex geological environments, steady-state surface NMR delivers representative estimates of $T_2$.