Modeling Porosity Evolution Throughout Reaction‐Induced Fracturing in Rocks With Implications for Serpentinization

C. Nasika, F. Donze, F. Renard, L. Scholtès, L. Zhang, X. Zheng
Journal of Geophysical Research-Solid Earth
Discrete element modeling, porosity pulse, reaction‐induced fracturing, rock hydration, volumetric expansion

Numerical modeling based on the discrete element method was used to explore the kinetics and mechanics of fractures induced by mineral volumetric expansion during rock hydration. Two systems were considered: the hydration of periclase into brucite and the hydration of peridotite into serpentine. We modeled the coupling between mineral transformation, stress, volume increase, and deformation by simulating the volumetric growth of discrete elements based upon an Avrami‐type kinetics equation. The model was implemented to consider the effects of stress and temperature on reaction kinetics as well as the alteration of material properties during hydration reactions. We were able to reproduce experimental evidences observed during the transformation of periclase into brucite, including volume growth, fracturing of periclase, formation of a porosity pulse, as well as the slow‐down effect of effective stress on the kinetics of the transformation. The model was also applied to study the serpentinization process. We estimated a bell‐shaped relationship between temperature and reaction rate of peridotite transformation following observations made during serpentinization experiments. For both periclase and peridotite systems, we characterized a relationship between the formation of a porosity pulse and the rate of fracture development within the medium. During serpentinization, the amplitude of the porosity pulse and the duration of this pulse depend on the reaction rate and, therefore, on the temperature. Our investigations provide geomechanical explanations on how native dihydrogen formed during serpentinization can be expelled and initiates its migration process.

Keywords: rock hydration, volumetric expansion, reaction‐induced fracturing, porosity pulse, discrete element modeling,

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