Methods and limitations of NMR data inversion for fluid typing.

Area of Science:

• Geophysics
• Petrophysics
• Nuclear Magnetic Resonance

Background:

• Nuclear Magnetic Resonance (NMR) is crucial for characterizing fluid properties in porous media.
• Traditional 2D NMR inversion methods can be data-intensive and time-consuming.
• Extracting fluid saturations and properties from limited NMR data remains a challenge.

Purpose of the Study:

• To develop and present two novel 1D NMR inversion methods for fluid saturation extraction.
• To provide faster alternatives to 2D NMR for fluid typing and analysis.
• To address limitations in NMR inversion methods, particularly concerning fluid typing ambiguity.

Main Methods:

• Introduced two 1D NMR inversion techniques varying echo spacing and wait time.
• Method 1: Used a shift matrix to link individual fluid T2 distributions to the apparent T2 distribution.
• Method 2: Employed a global evolution matrix for CPMG echo trains, considering T1, T2 relaxation, and diffusion.

Main Results:

• Successfully extracted fluid saturations and T2 distributions by minimizing differences between model and measured data.
• Demonstrated the utility of these methods for scenarios with insufficient data for 2D NMR.
• Highlighted the speed advantage of these 1D methods over 2D approaches for fluid typing.

Conclusions:

• The developed 1D NMR inversion methods provide efficient tools for fluid saturation analysis.
• These methods are valuable alternatives when 2D NMR is not feasible or too slow.
• Acknowledged inherent ambiguities in NMR fluid typing due to matrix singularities, suggesting prior knowledge can mitigate this.