| This dissertation explores the coupling of microstructural and continuum-scale failure through a fracture example, a bulk constitutive response example, and by developing a new AE signal processing technique. First, I explore the complexities of fracture propagation in Indiana Limestone by attempting to mimic two common fracture toughness test geometries (short-rod and notched 3-point bend) using a linear softening cohesive fracture model (LCFM). I find that the microstructural variations in shear strength and moduli relative to the strength and compliance of Indiana Limestone in tension lead to complications using the continuum-based LCFM. We find that the LCFM assumes that fracture processes remain constant in magnitude and timing throughout fracture propagation. The short rod tests comply with this requirement, but the notched 3-point bend tests do not. The second study focuses on understanding the deformation of the 3 sandstone lithofacies in the injection horizon in the Lower Tuscaloosa Formation at the SECARB Cranfield Detailed Area of Study'injection site. A range of compression tests were performed at near-reservoir conditions. To mimic reservoir conditions, tests were performed 100°C with 32 MPa pore pressure. Samples were saturated with a simulated brine that had been equilibrated with supercritical CO2. I find that (a) the weakening of some rock consituents, most likely the chlorite cements, through reaction with supercritical CO2 at temperature causes the onset of plastic strain before significant degradation of elastic moduli, (b) elastic moduli degradation obscures dilatant plastic strain, and (c) the weakening from the presence of CO2 is enough to cause the failure envelope of the conglomeratic sandstone facies (Facies A, the primary injection horizon) to decrease below the in situ stress estimates. My last study develops a new method to estimate the overlapping P-wave and S-wave arrival times in acoustic emissions (AEs). This is done by using filtered covariance metrics of scales of the continuous wavelet transform. This methodological advance will allow coupled estimates of AE locations, and independent estimates of changing bulk and shear modulus during failure. |
