On the calculation and interpretation of NMR relaxation time distributions

Keh Jim Dunn, G. A. LaTorraca, J. L. Warner, D. J. Bergman

Research output: Contribution to conferencePaperpeer-review

Abstract

We analyzed NMR relaxation time data using a multi-exponential model. The inversion of NMR data using such a model is an ill-posed problem. The answer is often not unique and requires subjective judgement. We studied two methods of regularization. One uses norm smoothing based on an article by Butler et al. We found that optimal norm smoothing depends on the input of measurement errors. The second method uses curvature smoothing which minimizes variations in the second derivative. The latter is more effective for suppressing fluctuations in the relaxation time distribution, but doesn't directly account for data quality. We studied NMR T1 data at full and partial saturations with desaturation pressures ranging from 15 to 400 psi (air/brine). As a general guideline, we found that the relaxation time cutoff which corresponds to irreducible water saturation is about 33 ms. For a limited number of samples, we found that the T1 relaxation time distribution has very little dependence on the frequency from 200 down to 1 MHz. We also found that T2 could be correlated to permeability.

Original languageEnglish
Pages45-54
Number of pages10
StatePublished - 1994
Externally publishedYes
EventProceedings of the SPE Annual Technical Conference & Exhibition - New Orleans, LA, USA
Duration: 25 Sep 199428 Sep 1994

Conference

ConferenceProceedings of the SPE Annual Technical Conference & Exhibition
CityNew Orleans, LA, USA
Period25/09/9428/09/94

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