5:15 PM - 6:45 PM
[SCG46-P23] Deformation experiments of the Oman peridotite and the effect of carbonation on the physical properties
Keywords:Carbon mineralization, Carbon capture and storage, Peridotite, Listvenite, Triaxial deformation experiment
Carbon mineralization has been proposed as a new method of CO2 sequestration in carbon capture and storage (CCS), one of the measures to combat climate change. This method involves CO2 injection into mafic or ultramafic rocks, such as basalt or peridotite, and stores it as carbonated minerals formed by reactions between CO2 and the rocks. This technique has several advantages, such as low risk of CO2 leakage and high sequestration potential compared with conventional sequestration in porous rock formations. In fact, carbon mineralization in basalt layers has been implemented since 2014 in a project called CarbFix in Iceland.Regarding the mineralization of CO2 in peridotite, ophiolites, which are large rock bodies formed when oceanic crust was uplifted in the past and deposited on continental crust, are potential sites. This is because mantle peridotite is widely exposed in these areas. Consequently, they are likely to be suitable for large-scale sequestration. However, carbon mineralization in peridotite has not been practical yet because some problems remain, such as the lack of indicators to quantify the abundance of carbonate minerals in peridotite after CO2 injection. Therefore, I conducted an experimental study focusing on physical properties of rocks, especially fracture strength and elastic velocity, to investigate whether physical properties of rocks are available to assess carbonate minerals in peridotite after CO2 injection.
In this study, I prepared five listvenites, carbonated peridotites, with different abundances of carbonate minerals mined in the Samail ophiolite in Oman. The mineral compositions of the samples were determined by EPMA mapping. The carbonate minerals in the samples were calcite and dolomite, and the carbonate mineral abundance of each sample was calculated from the sum of these carbonate minerals, ranging from 0.3 to 95.8%. I performed triaxial compression tests on these samples under dry conditions at a confining pressure of 20 MPa, room temperature and a strain rate of approximately 10-6 s-1.
Strain analysis showed that Young's modulus decreased with increasing carbonate content in samples containing more than 52% carbonate minerals. Fracture strength was calculated from axial displacement, and the three samples containing more than 25% quartz had higher fracture strengths than unaltered peridotite. Conversely, the other two samples with more than 86% carbonate minerals had lower fracture strengths, indicating a correlation between fracture strength and carbonate mineral abundance. While all samples had lower elastic wave velocities than unaltered peridotite, there was no clear correlation between carbonate mineral content and elastic wave velocity. However, compared with the elastic wave velocity of serpentinized peridotite, it suggested that serpentinization increased Vp/Vs values while carbonation either maintained or decreased them.
The mechanical results obtained from the experiments suggest that quartz and carbonate minerals formed by carbonation of peridotite affect the fracture strength of listvenite. In other words, the fracture strength of listvenite may be useful to estimate the mineral composition of listvenite and then quantify the amount of carbonate minerals. As for elastic wave velocity, it is difficult to directly evaluate the abundance of carbonate minerals, although the Vp/Vs values suggest that it is possible to estimate whether the peridotite has undergone carbonatation or serpentinization. These results suggest that rock physical properties may be available to monitor carbonated peridotite.
In this study, I prepared five listvenites, carbonated peridotites, with different abundances of carbonate minerals mined in the Samail ophiolite in Oman. The mineral compositions of the samples were determined by EPMA mapping. The carbonate minerals in the samples were calcite and dolomite, and the carbonate mineral abundance of each sample was calculated from the sum of these carbonate minerals, ranging from 0.3 to 95.8%. I performed triaxial compression tests on these samples under dry conditions at a confining pressure of 20 MPa, room temperature and a strain rate of approximately 10-6 s-1.
Strain analysis showed that Young's modulus decreased with increasing carbonate content in samples containing more than 52% carbonate minerals. Fracture strength was calculated from axial displacement, and the three samples containing more than 25% quartz had higher fracture strengths than unaltered peridotite. Conversely, the other two samples with more than 86% carbonate minerals had lower fracture strengths, indicating a correlation between fracture strength and carbonate mineral abundance. While all samples had lower elastic wave velocities than unaltered peridotite, there was no clear correlation between carbonate mineral content and elastic wave velocity. However, compared with the elastic wave velocity of serpentinized peridotite, it suggested that serpentinization increased Vp/Vs values while carbonation either maintained or decreased them.
The mechanical results obtained from the experiments suggest that quartz and carbonate minerals formed by carbonation of peridotite affect the fracture strength of listvenite. In other words, the fracture strength of listvenite may be useful to estimate the mineral composition of listvenite and then quantify the amount of carbonate minerals. As for elastic wave velocity, it is difficult to directly evaluate the abundance of carbonate minerals, although the Vp/Vs values suggest that it is possible to estimate whether the peridotite has undergone carbonatation or serpentinization. These results suggest that rock physical properties may be available to monitor carbonated peridotite.