Study of Hydrated Clay Reactions to Various Cations Using Low-Field NMR

ABSTRACT

Low-field NMR has been used in downhole logging tools for fluid and petrophysical evaluation of many petroleum reservoirs. In heavy oil and oil sand formation evaluation, clays have a signature response to low field NMR, that is similar to that of oil. A further study of clays alone is the key to evaluate and to better understand clay-water interactions in a fast and non-destructive way. Clays can be found throughout many sectors of the petroleum industry. From reservoir evaluation to environmental pollution, clays are known to have swelling properties that can pose problems including plugging of pore throats within the reservoir or possible lateral movement of contaminants on the surface. This paper is part of a larger study on clay characterization with low-field NMR. Of particular interest in this study is the interaction of clays with high salinity brines. Clays are typically surrounded by ionequilibrated water prior to exposure to high cation-content brines. In this study, four types of clays are used: kaolinite, illite, calcium-montmorillonite and sodium-montmorillonite. The clays are initially hydrated with distilled water and are then exposed to varying cation solutions. The cations used are Na +, Ca 2+ and Mg 2+, which are readily found in formation brines. NMR spectra of clays exposed to brines tend to show distinct characteristics of both amplitude and mean relaxation. Analysis of the NMR spectra correlates the NMR response to clay-chemistry of the individual clays.

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