Fluid Typing and Pore Size in Organic Shale Using 2D NMR in Saturated Kerogen Isolates
- Philip M. Singer (Rice University) | Zeliang Chen (Rice University) | George J. Hirasaki (Rice University)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- December 2016
- Document Type
- Journal Paper
- 604 - 619
- 2016. Society of Petrophysicists & Well Log Analysts
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- 281 since 2007
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There is increasing evidence that 2D T1-T2 NMR can be used for fluid typing and saturation in organic shale. More specifically, it has been generally observed that in organic-shale cores the T1/T2 ratio is higher for saturating hydrocarbons than for saturating water, which could be exploited as a technique for an NMR saturation log in unconventional reservoirs. This paper presents a fundamental study into the 2D NMR response of saturating fluids in the organic-matter pores of pelletized kerogen isolates, without complications from saturation history and wettability alteration of the organic pores.
In the case of heptane-saturated kerogen pellets, the T1-T2 map indicates two distinct peaks. One peak has a similar porosity to a random bead-pack, and is interpreted as heptane in the intergranular kerogen pores created during pelletization. The other peak has a large T1/T2 ratio, and is interpreted as intragranular or “absorbed” heptane in kerogen, possibly from bitumen-coated kerogen pores.
The T1/T2 ratio for heptane-saturated kerogen is found to be consistently larger than for water-saturated kerogen, across the entire T2 spectrum. The isolated kerogen results are compared with the saturated organic-shale rock (the same source rock used for the kerogen isolates) and with pelletized clay isolates, all of which corroborate with larger T1/T2 ratios for saturating hydrocarbons versus saturating water, thereby validating T1/T2 ratio as a technique for fluid typing and saturation in organic shale.
The NMR pore-size distribution and heterogeneous surface relaxivity of heptane-saturated kerogen are determined by integration with BET surface-area data, and are validated with SEM images. Data for kerogen saturated with partially deuterated water indicates that the hydrogen-hydrogen dipole-dipole interaction contributes to the underlying surface-relaxation mechanism in organic nanopores, which has broad implications on the interpretation of NMR measurements in organic nanopores.
|File Size||6 MB||Number of Pages||16|