Speaker
Description
Carbon mineralization is considered the most stable method for long-term carbon storage. Carbon mineralization is favored in mafic/ultramafic rocks due to their high content of reactive minerals which efficiently react with CO2 to form solid carbonates. We have spent the past few years exploring how NMR can be used to quantify changes in pore size distributions and pore surface relaxivity as a function of alteration, particularly carbon mineralization, in these rocks.
We have pursued experiments along two fronts. Firstly, NMR measurements on pre- and post-reacted samples are utilized to observe changes in T2-derived pore size distribution within plugs subjected to thermal fracturing and reactive CO2 transport core flood experiments. Secondly, the T2 distributions of a large suite of Newberry Volcano basalt samples from various depths have been recorded and integrated with other petrophysical data. In addition to the T2 data, SEM- and BET-based partial pore size distributions were also recorded on these samples. This data allowed the T2 relaxation time to be calibrated to pore size and the surface relaxivity of each sample derived. Correlating this surface relaxivity to alteration of the pores has given important insight into how carbon mineralization can effect pore surface chemistry.
In the first series of experiments, a highly reactive ultramafic dunite sample was exposed to CO2-laden brine. The sample was then saturated with inert fluid and the resulting T2 distribution was recorded. This distribution was then compared with that of a twin sample that had not undergone exposure to CO2. The pore volume of the sample which had undergone CO2 brine flow was reduced by nearly twenty percent as compared to its twin. This reduction in pore volume can be attributed to carbon mineralization.
In the second set of experiments, the T2 distribution of two different basalt core samples, one fresh sample and one altered by exposure to gases and in situ water were measured. In addition to the T2 distributions, partial SEM pore size distributions were also recorded. These distributions were employed to calibrate the T2 relaxation time with pore radius and derive a surface relaxivity constant for each basalt sample. The results showed that there is clearly a correlation between surface relaxivity with fresh vs altered samples.
The results display that NMR core analysis can be a valuable tool in assessing the feasibility of wells for carbon sequestration and storage.
| Country | Canada |
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