NMR physics

Today, I reviewed the basic knowledge of NMR so that I would be able to find the proper predictors of it.

Summary

Data selection

No diaelectric data because they are also very expensive.

Try to use GR, neutron, sonic, density, resistivity data to predict NMR.

NMR:

NMR porosity is independent of matrix minerals, and the total response is very sensitive to fluid properties. Differences in relaxation times and/or fluid diffusivity allow NMR data to be used to differentiate clay-bound water, capillary-bound water, movable water, gas, light oil, and viscous oils. NMR-log data also provide information concerning pore size, permeability, hydrocarbon properties, vugs, fractures, and grain size.

T1: the longitudinal relaxation time.

T2: the transverse or spin-spin relaxation.

The decay or relaxation time of the NMR signals (T2) is directly related to the pore size. The NMR signal detected from a fluid-bearing rock therefore contains T2 components from every different pore size in the measured volume. Using a mathematical process known as inversion, these components can be extracted from the total NMR signal to form a T2 spectrum or T2 distribution, which is effectively a pore size distribution.

The so-called ‘T2 cut-off’ in a T2 distribution is the T2 value that divides the small pores that are unlikely to be producible from the larger pores that are likely to contain free fluid. The integral of the distribution above the T2 cut-off is a measure of the free fluid (mobile fluid) in the rock.  The portion of the curve below the cut-off is known as bound fluid and is made up of the clay bound fluid and the capillary bound fluid.

Tomorrow, I will continue to learn more about NMR and try to find the proper predictors.