NMR Evaluation of Light-Hydrocarbon Composition, Pore Size, and Tortuosity inOrganic-Rich Chalks

Zeliang Chen, Philip M. Singer, Xinglin Wang, Harold J. Vinegar, Scott V. Nguyen, George J. Hirasaki

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


In this paper, we use core-log integration to estimate the hydrocarbon composition, pore size, and tortuosity in an organic-rich chalk formation. Our core analysis consists of pressure saturation of the as-received reservoir core plugs followed by in-situ NMR T1-T2 and D-T2 measurements. The saturating fluids include water and light hydrocarbons, including methane,  ethane, propane, n-butane, n-pentane, and n-decane. The laboratory-measured T2 distributions of the hydrocarbon-saturated cores are converted to the downhole T2app (T2 apparent) log by simulating the effects of diffusion in the magnetic-field gradient of the NMR logging tool. The simulated T2app log is compared to the actual log to estimate the qualitative downhole hydrocarbon composition by minimizing the least-squares error. The simulated downhole T1/T2app based on the laboratory-measured T1/T2 illustrates contrasts between saturating fluids and, therefore, can be used for qualitative fluid typing. We also find that methane and natural gas liquids (NGLs) can be well distinguished from water and heavier hydrocarbons by applying T2app and T1/T2app 2D cutoffs. The laboratory-measured restricted diffusivity indicates that the saturating methane can be distinguished from liquid-state hydrocarbons by its higher diffusivity. In addition, the laboratory-measured restricted diffusivities of different light hydrocarbons are fitted to the Padé approximation to estimate the mean pore size, heterogeneity length scale, and tortuosity of the light-hydrocarbon filled porosity.

Original languageEnglish
Pages (from-to)771-797
Number of pages27
Issue number6
StatePublished - 1 Dec 2019
Externally publishedYes

ASJC Scopus subject areas

  • Geotechnical Engineering and Engineering Geology


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