The effect of wait time on T2 distributions from NMR experiments

Area of Science:

• Geophysics
• Petrophysics
• Nuclear Magnetic Resonance Spectroscopy

Background:

• Nuclear magnetic resonance (NMR) relaxation is crucial for characterizing porous media.
• Accurate interpretation of NMR relaxation data, particularly T2 distributions, is essential for reservoir characterization.
• The influence of experimental parameters like wait time on T2 distributions requires careful consideration.

Purpose of the Study:

• To investigate the impact of varying wait times on T2 distributions obtained from NMR relaxation measurements.
• To evaluate the effectiveness of a wait time correction method for restoring accurate T2 distributions.
• To analyze brine-saturated core plugs using Carr-Purcell-Meiboom-Gill (CPMG) sequences.

Main Methods:

• Measured T1 and T2 relaxation curves at 1 MHz on two brine-saturated core plugs.
• Extracted T2 distributions using Carr-Purcell-Meiboom-Gill (CPMG) sequences with varied wait times.
• Analyzed T2 distributions using both limited exponential fitting and continuous B-spline basis methods.

Main Results:

• T2 distributions exhibited strong dependence on the wait time between echo sequences.
• Analysis using a continuous B-spline basis demonstrated this wait time dependency.
• A wait time correction method successfully restored the T2 distributions to their true values.

Conclusions:

• Wait time is a critical experimental parameter affecting NMR T2 distributions in core plugs.
• The application of a wait time correction is necessary for accurate quantitative analysis of NMR relaxation data.
• This study highlights the importance of accounting for experimental conditions in NMR petrophysical analysis.