Experimental Study of the Effects of Wettability and Fluid Saturation on Nuclear Magnetic Resonance and Dielectric Measurements in Limestone
- Lalitha Venkataramanan (Schlumberger Doll Research) | Martin D. Hurlimann (Schlumberger Doll Research) | Jeffrey A. Tarvin (Schlumberger Doll Research) | Kamillah Fellah (Schlumberger Doll Research) | Diana Acero-Allard (Schlumberger Doll Research) | Nikita V. Seleznev (Schlumberger Doll Research)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- December 2014
- Document Type
- Journal Paper
- 572 - 586
- 2014. Society of Petrophysicists & Well Log Analysts
- 4 in the last 30 days
- 383 since 2007
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Results from experiments on three identical samples of oolitic limestone show the systematic effects of wettability and fluid saturation on nuclear magnetic resonance (NMR) and dielectric data in rocks partially saturated with brine and crude oil. Mercury porosimetry and image analysis of the samples indicate that the pore distribution is bimodal. All samples are from the same outcrop rock and are initially water-wet. They are systematically put through the complete saturation cycle. Midway through the cycle, the wettability of two of the samples is changed to mixed-wet by aging the samples. NMR, resistivity and dielectric measurements are performed at different stages of fluid saturation and wettability. Since the samples are identical in their petrophysical properties, it is possible to relate the differences between samples or different saturation stages to differences in wettability and/or fluid saturations. It is observed that wettability has a significant effect on NMR, dielectric and resistivity data. The relative permeabilities of the samples may also depend on wettability; this is evidenced in the presence of a trapped water phase in the mixed-wet samples. By helping improve our understanding of the effects of wettability and fluid saturations on NMR, resistivity and dielectric data, we expect that this study will be useful in exploring new avenues in the future, for integrating these measurements.
Wettability of a rock describes the preference of rock grains to be in contact with one fluid rather than another. The constituents of the rock grains, brine chemistry and oil composition play a role in governing rock wettability (Buckley and Monsterleet, 1998). Most reservoirs are thought to be water-wet prior to oil migration. Oil wettability affects the relative permeability of oil and water and therefore plays a critical role in primary and secondary recovery (Abdallah et al., 2007).
In a porous medium partially saturated with oil and water, water-wet (WW) and oil-wet (OW) rocks define the end members of a continuum, in which the surface prefers contact with water and oil, respectively. In a conceptual image of a WW rock, oil is considered to be in the center of all pores. The reverse holds true for an OW rock, with water at the center of pores. In a mixed-wet (MW) rock, some of the surfaces of the pores have a preference for oil while other parts of the surfaces and smaller pores are thought to have a preference for water (Salathiel, 1973).
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