Abstract
This paper summarizes experimental studies using Nuclear Magnetic Resonance (NMR) to evaluate cement porosity, pore size distribution, and other characteristics such as Calcium Silicate Hydrate (CSH) gel structure and morphology. The first known paper on NMR experiments to investigate cement pastes was published in 1978. Two main NMR parameters, the so-called longitudinal T1 and transverse T2 relaxation times, are commonly measured and analyzed, representing the water response which is trapped in the cement. The hydration process reported in this paper was found to be monitored from as low as 10 min to longer than 365 days. Other studies conducted experiments by using NMR, especially during the 1980s. These studies employed variations in methodologies and frequencies, making data comparison difficult. Additionally, different spectrometers and NMR concepts, as well as operating characteristics, were used. Therefore, it is challenging to reconcile results from previous NMR studies on cement. Other significant hurdles are different cement types, water/cement ratio, and curing conditions. One notable observation is that there has not been any comprehensive laboratory work related to NMR on oilfield cement types, including porosity and hydration. Two recent studies have presented NMR measurements on class G and class H cements.
Highlights
Materials such as cement or rock contain pores that are filled with a fluid, typically water
Our paper has shown that Nuclear Magnetic Resonance (NMR) is useful in characterizing cement properties that are Our paper has shown that NMR is useful in characterizing cement properties that are valuable for well integrity studies, the cement porosity evolution
We found that two major NMR methods are commonly used today: H NMR, which investigates the hydrogen spin and provides information about the water trapped and porosity, and Si magnetic spinning angle (MAS) NMR, which focuses on identifying the nanostructure of silicate composites
Summary
Materials such as cement or rock contain pores that are filled with a fluid, typically water. The water contains hydrogen, which possesses a single proton. These protons can be activated and aligned by the application of a magnetic field. The initial alignment strength is directly proportional to the number of hydrogen atoms in the system; this is a measure of porosity in most cases. An oscillating magnetic field is applied to tip the protons away from this alignment. The rate at which these protons realign depends on surface relaxivity, viscosity, and pore size. The realignment analysis produces a spectrum of relaxation times, which represent a distribution of pore bodies in typical cases
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