Experimental Study of the Effect of Porosity on EICP Biomineralization in Dolostone and Shales Under Uniaxial Compressive Stress Condition

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.