Speaker
Description
Nuclear magnetic resonance (NMR) techniques have been used extensively for studying fluid behaviour in porous rocks, mainly through complementing other experimental processes, such as core flooding, as well as through NMR logging techniques. Common applications of these methods include determining the pore size distribution of the porous media, wettability characterization and fluid identification (Guo et al., 2020).
In this study, simple porous materials have been used as a substitute for rock samples, in order to look at the fundamentals behind the behaviour of brines within different porous media, which is of particular importance in applications such as enhanced oil recovery and CO2 sequestration. Specifically, NMR relaxation/diffusion experiments have been performed on silica gel and alumina catalyst pellets, saturated with NaCl brines of various salinities (from pure water to 25% w/v NaCl) in order to investigate the effects of salinity on the water behaviour in terms of thermal diffusion and adsorption within the pore structures.
The ratio between the longitudinal and transverse NMR relaxation times $T_{1}/T_{2}$ is known to be proportional to the strength of the surface interactions between the fluid and the solid surfaces of the porous medium (D’Agostino et al., 2014). In our experiments, by increasing the salinity of the brines, a steady decrease in $T_{1}/T_{2}$ has been observed for the brines within the alumina samples, while a slight increase has been observed in the $T_{1}/T_{2}$ values of the brines within the silica samples. The results therefore suggest that increasing the NaCl concentration weakens the surface interactions between the brines and the alumina, while it strengthens the interactions between the brines and the silica pore surfaces.
A steady decrease in the NMR diffusion coefficients of the brines has also been observed in both alumina and silica porous media. This implies that the presence of NaCl within the solution hinders the mobility of the liquid within the pore structures. These results are consistent with the increase in viscosity due to increased NaCl concentration as observed by other studies (Kwak et al., 2005), but could also be partially attributed to salt precipitation/deposition blocking the pore pathways.
References
Guo, J.-C. et al. (2020) ‘Advances in low-field nuclear magnetic resonance (NMR) technologies applied for characterization of pore space inside rocks: a critical review’, Petroleum Science, 17(5), pp. 1281–1297. doi: 10.1007/s12182-020-00488-0.
D’Agostino, C., Mitchell, J., Mantle, M. D., & Gladden, L. F. (2014). Interpretation of NMR Relaxation as a Tool for Characterising the Adsorption Strength of Liquids inside Porous Materials. Chemistry (Weinheim an Der Bergstrasse, Germany), 20(40), 13009. https://doi.org/10.1002/CHEM.201403139
Kwak, H. T., Zhang, G., & Chen, S. (2005, August). The effects of salt type and salinity on formation water viscosity and NMR responses. International Symposium of the Society of Core Analysts.
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| Country | United Kingdom |
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