NMR Relaxometry in Shale and Implications for Logging
- Ravinath Kausik (Schlumberger-Doll Research) | Kamilla Fellah (Schlumberger-Doll Research) | Erik Rylander (Schlumberger) | Philip M. Singer (Schlumberger) | Richard E. Lewis (Schlumberger) | Steven M. Sinclair (Matador Resources Company)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- August 2016
- Document Type
- Journal Paper
- 339 - 350
- 2016. Society of Petrophysicists & Well Log Analysts
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- 422 since 2007
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The quantity of light hydrocarbon and natural gas in tight-oil and gas shales respectively is one of the primary indicators of reservoir quality (RQ). The measurement of RQ therefore depends on the ability to distinguish the quantity of the light oil or gas from other fractions of the total organic carbon, namely the immobile hydrocarbons such as kerogen, bitumen, heavy oil and formation water. Additionally, the separation of the oil into fractions hosted in organic versus inorganic porosity is important for determining the potentially producible fraction. Although multidimensional diffusion-relaxation correlation experiments can distinguish hydrocarbons from other fluids in conventional reservoirs, their use is restricted owing to the presence of short relaxation times in most tight-oil and gas-shale plays. We demonstrate the feasibility of nuclear magnetic resonance (NMR) relaxometry for determining the different constituents in shale based on the frequency dependence of their relaxation times, using 2D NMR T1-T2 experiments. We determine the 2D T1- T2 relaxation distributions of the different fluid fractions in unconventional shale plays, and comprehend the T1/ T2 ratios based on the intrinsic relaxation mechanisms of each component. We also discuss the practical implications of these relaxation mechanisms by determining which fractions are identifiable in low-field NMR logs, thereby setting limits to fluid typing and saturation determinations, downhole. The NMR experiments discussed here together with associated log analysis could enable in-situ estimates of the potentially producible fluid volumes, thereby aiding well placement, completion methodologies and production predictions.
Nuclear magnetic resonance (NMR) core-analysis applications have been recently shown to be vital for the characterization of gas-shale samples. These studies have led to the understanding of the dynamics of the free and adsorbed gas in the kerogen nanopores, the relaxation distributions of the clay-bound water and methane gas in nanopores, and the effect of adsorption on the gas hydrogen index (Kausik et al., 2011). The understanding of the NMR relaxation and diffusion properties of the free and adsorbed gas, together with that of clay-bound water have also led to the development of new logging applications in these formations (Hook et al., 2011, Cao Minh et al., 2012). Furthermore, high-field NMR relaxometry based techniques have shown to be useful for monitoring gas transport and pressure induced fracturing in gas-shale samples (Wang et al., 2014).
|File Size||8 MB||Number of Pages||12|