(760e) Geomechanical and Geochemical Influences On the Permeability of Wellbore Cement Fractures Exposed to CO2-Rich Brine: An Experimental and Modeling Study

The objective of this work was to explore and quantify the relationships between chemical alteration, deformation, and permeability at the wellbore/caprock interface important to long-term geologic carbon storage through experiment and modeling.  The core flood experiments span variable pCO₂, flow rate, and cement – caprock fracture apertures at 60°C and 24.8 MPa.  We used x-ray computed micro tomography to spatially resolve the fracture surface and the extent of alteration, three dimensional digital image correlation to spatially resolve plastic deformation resulting from chemical alteration, and time dependent solution chemistry and pressure to track coupled evolution of chemical alteration and mechanical deformation.  The experimental data are used to constrain models of wellbore/caprock interface using a numerical simulator that couples reaction front chemistry, flow and transport of dissolved species, and elastic and plastic deformation.

Coupled processes between chemical alteration and material compressibility were largely responsible for decrease in permeability despite measured porosity increase at the cement/caprock interface as a result of the chemical alteration.  Our results show that CO₂-rich brines alter wellbore cement into distinct portlandite depleted, carbonate, and aluminum-bearing amorphous silicate layers and change the compressibility of cement at the wellbore/caprock interface.   Furthermore, dissolution of portlandite from the cement resulted in plastic deformation of the surface contacts enabling fluid flow paths. The deformation restricts flow paths and lowers the overall permeability.  Chemical alteration of the cement was controlled by diffusion of reactants and products through cement and its alteration layers, as well as calcite equilibrium at the carbonate/amorphous silicate boundary and analcime equilibrium at cement/caprock interface.