Numerical investigation of mineralogical composition effect on strength and micro-cracking behavior of crystalline rocks

Mineralogical composition has a great influence on the mechanical behavior and the micro-cracking process of crystalline rocks for CO2 and natural gas storage. This study numerically investigates the influence of mineralogical composition (i.e., quartz content) of a dominantly felsic phaneritic igneous rock with respect to rock strength and the associated micro-cracking behavior using a grain-based modeling approach in two-dimensional Particle Flow Code (PFC2D). First, numerical specimen models with different mineralogical compositions are generated. The generated numerical models have the same geometry of the assembled grain structure to minimize the effect of grain scale heterogeneity on the simulation results. Micro-parameters previously calibrated to match the macro-properties of the Bukit Timah granite are then assigned to the numerical models. In the numerical simulation of uniaxial compression tests, the strength and Young's modulus are found to increase with the increase of quartz content in the numerical model, while the Poisson's ratio and the maximum volumetric strain gradually decrease. The simulated strength behavior is in good agreement with the laboratory test results obtained from previous studies. However, the crack damage stress seems not to be affected by the quartz content. The total number of generated micro-cracks is also found to gradually increase as the quartz content in the numerical model increases. The rock strength shows a good correlation with the total number of generated micro-cracks. Two mechanisms are identified to initiate the nearly vertical macroscopic fractures which are generated in tension. At last, the influence of spatial distribution of mineral grains on the simulated strength property and micro-cracking behavior is discussed.