This paper addresses how the surface relaxivity, ρ, of rock forming minerals as assesed from low field Nuclear Magnetic Resonance (NMR) spectrometry, is affected by temperature and Larmor frequency. This is relevant for connecting laboratory data and reservoir logging data while increasing the accuracy of predictions of petrophysical properties of various rocks with the use of NMR spectrometry. We perform laboratory transverse relaxation (T2) measurements on water saturated Gorm field chalk, Stevns Klint chalk, Solsort field greensand and Berea sandstone. These rocks are of particular interest in studies related to the North Sea oil and gas reservoirs, since they cover a wide range of formations, ranging from homogeneous to inhomogeneous chalk, chloritic and quartz mineralogy. Comparison of T 2 distributions at Lamor frequency of 2 and 20 MHz at 40 Â°C shows that paramagnetic minerals in the Gorm field chalk and Solsort field greensand have higher ρ at higher Larmor frequency. By contrast, ρ of the purely calcitic Stevns chalk and quartzitic Berea sandstone proved not to be affected by the changes in frequency. T2 distributions at temperatures ranging from 10 °C to 60 °C provided comparison between lab and field T2 measurements: ρ for calcite decreases with temperature; whereas ρ for quartz increases with temperature. These findings illustrate differences in the porosity and pore size distribution obtained in the lab, compared to those from logs using NMR tools.
- Nuclear magnetic resonance
- Surface relaxivity
- Larmor frequency
Katika, K., Fordsmand, H., & Fabricius, I. L. (2018). Low field NMR surface relaxivity studies of chalk and argillaceous sandstones. Microporous and Mesoporous Materials, 269, 122-124. https://doi.org/10.1016/j.micromeso.2017.06.035