[SCG49-P08] Numerical simulations for reaction-induced fracture formation of layered gabbro during hydration process
Keywords:Oman Drilling Project, layered gabbro, permeability, Discrete Element Method, serpentinization
We conducted the two-dimensional DEM model, and the details of the model follows Okamoto and Shimizu (2015) and Shimizu and Okamoto (2016). We consider a simple volume increasing hydration reaction (A + H2O → B; 50% volume increase), and the reaction rate is defined as a linear function of fluid pressure. In the model, advective fluid flow occurs through apertures between particles, in response to difference of fluid pressure of individual domains. The rock model is consist of reactive part (it can change from olivine to sperneitne) and non-reactive part (e.g., plagioclase and clnopyronene). The reaction rate constant and aperture width of matrix and fracture are defined based on the non-dimensional numbers based on Shimizu and Okamoto (2016).
Firstly, we conducted the simulations for the model in which a single olivine exists in non-reactive matrix. When fluid is supplied through matrix, hydration of olivine starts, which produces the mesh-like textures inside the olivine grain and radial cracks within the unreactive matrix, which is consistent with those observed in the gabbro sample from CM1A. Second, we conducted a case where several olivine grains exist in matrix. In this case, we found the formation of fracture network that connects among the olivine grains, and positive relationship between the reaction rate and permeability. Finally, we tested the case of the layered structure that consists of olivine-rich layer and olivine-absent layer, and that fluid flows in direction perpendicular to the layers. The results of the simulations reveals that the development of vertical fractures in both olivine-rich and non-reactive layers, whereas the horizontal fractures are only developed in the olivine-rich layers. These features of fracture orientation are consistent with the natural observations and indicate that he reaction-induced fracturing could significantly enhance the fluid infiltration through layered gabbro.
Katayama I, Terada T, Okazaki K, Tanikawa W (2012) Nat Geosci 5:731–734.
Jamtveit B., Malthe-Sørenssen A., Kostenko O., 2008. Earth Planet. Sci. Lett., 267, pp. 620-627
Okamoto,A.,Shimizu,H., 2015. Earth and Planetary Science Letters 415, 9–18.
Shimizu, H., Okamoto, A., 2016. Contributions to Mineralogy and Petrology, 171, 73.