Biogeochemical-induced rock alteration is an evolving process that focuses on harnessing biologically induced chemical activities to change the mechanical properties and behavior of rocks. It often relies on enzyme-induced carbonate precipitation (EICP) which utilizes biomineralization by promoting the formation of calcium carbonate (CaCO3) in the rock pores and fractures. However, there is still a lack of knowledge on the effect of porosity on biomineralization in rocks from a mechanistic view. This study uses an experimental method to investigate the core-scale thermo-biogeomechanical alterations in low-permeability clay-rich rock (shale) and in high permeability dolomitic rock using the EICP treatment method. We first conducted EICP treatment of shale and dolostone samples using jack bean urease enzyme over a 3-day period at a distinct temperature. Subsequently, the mechanical properties were measured using uniaxial compression test. Finally, we analyzed the pre- and post-treatment changes in the dolomite-rich and shale rock samples to better understand the effect of enzyme-induced calcite precipitates on mechanical response of the rock samples. The results suggest that in dolostones with higher porosity, carbonate precipitation will have a greater impact on the mechanical properties than in shales with ultra-low porosity, when treated with EICP.
Biogeochemical processes can enhance mechanical and flow (porosity and permeability) properties of rocks (Phillips et al., 2015; Kirkland et al., 2020; Kolawole et al., 2021). Prior research has provided insights into the impact of such complex processes for various geotechnical and energy engineering applications (Kolawole et al., 2021, 2022; Whiffin et al., 2007; Gao et al., 2019; Kolawole et al., 2023; Kolawole, 2023). For instance, Kolawole et al. (2022) evaluated the effect of bio-induced precipitation on tight carbonates for long-term storage integrity. To investigate this, biological media was injected into low-porosity carbonate samples for 30 days and the mechanical strength of the treated samples was measured using the uniaxial compression test. The results of the study showed an increase (>100%) in Uniaxial Compressive Strength (UCS) of the carbonate samples. This increase in rock strength suggests that biogeomechanical alterations can enhance the strength of rocks and facilitate security of low-porosity carbonate caprocks.
