Temperature Correction Models for NMR Relaxation Time Distribution in Carbonate Rocks
- Gabor Hursan (Saudi Aramco) | Shouxiang Ma (Saudi Aramco) | Wei Shao (Halliburton Energy Services) | Songhua Chen (Halliburton Energy Services)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- SPWLA 60th Annual Logging Symposium, 15-19 June, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors
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To date, nuclear magnetic resonance (NMR)-based formation evaluation interpretation models are developed and/or calibrated with laboratory core analysis conducted at ambient conditions, partially because high temperature laboratory NMR measurements are limited by instrument capabilities and also costly. Currently, the underlying assumption is that the difference between NMR relaxation time distributions measured at ambient conditions and those obtained from in-situ logs is negligible. While this may be true for reservoirs with major contrasts in their NMR relaxation properties, the environmental effect needs to be accurately described and properly corrected in complex carbonate reservoirs where NMR logs must detect subtle pore size variations with high sensitivity.
This paper describes data analytics approaches to derive a temperature correction model for T2 distribution data using laboratory NMR core measurements at four temperatures. Even though, ideally, a data analytics approach requires a great number of experiments, the simple method employed for the carbonate field in this study works well with a limited number of samples (28). With the temperature correction models, the laboratory developed NMR-based interpretation models can be adjusted to in-situ reservoir temperatures, thereby applicable to NMR logging interpretations. To the knowledge of the authors, this is the first systematic attempt in the industry to develop a spectral NMR temperature correction model for in-situ carbonate formation interpretation.
The temperature dependence of NMR relaxation times of fluids in porous media remains an unsolved challenge. Theoretical and experimental NMR studies in carbonates (Godfrey, et al, 2001a; Godfrey, et al, 2001b; Straley, 2002; Kwak et al., 2016) identified several mechanisms leading to different, if not opposite, temperature dependencies. In complex pore systems, such as carbonate rocks, the overall temperature dependence is likely governed by multiple underlying mechanisms with no straightforward first principle-based description. Therefore, no comprehensive temperature correlations of key NMR logging deliverables, such as the distributions and geometric means of T1 or T2, are available.
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