Pore-scale Study of Bio-mineral and Bio-gas Formations in Porous Media

The potential of using bio-geo-chemical processes for applications in geotechnical engineering has been widely explored in order to overcome the limitation of traditional ground improvement techniques. Biomineralization via urea hydrolysis, referred to as Microbial or Enzymatic Induced Carbonate Precipitation (MICP/EICP), has been shown to increase soil strength by stimulating precipitation of calcium carbonate minerals, bonding soil particles and filling the pores. Microbial Induced Desaturation and Precipitation (MIDP) via denitrification has also been studied for its potential to stabilize soils through mineral precipitation, but also through production of biogas, which can mitigate earthquake induced liquefaction by desaturation of the soil. Empirical relationships have been established, which relate the amount of products of these biochemical processes to the engineering properties of treated soils. However, these engineering properties may vary significantly depending on the biomineral and biogas formation mechanism and distribution patterns at pore-scale. This research focused on the pore-scale characterization of biomineral and biogas formations in porous media.

The pore-scale characteristics of calcium carbonate precipitation via EICP and biogenic gas formation via MIDP were explored by visual observation in a transparent porous media using a microfluidic chip. For this purpose, an imaging system was designed and image processing algorithms were developed to analyze the experimental images and detect the nucleation and growth of precipitated minerals and formation and migration mechanisms of gas bubbles within the microfluidic chip. Statistical analysis was performed based on the processed images to assess the evolution of biomineral size distribution, the number of precipitated minerals and the porosity reduction in time. The resulting images from the biomineralization study were used in a numerical simulation to investigate the relation between the mineral distribution, porosity-permeability relationships and process efficiency. By comparing biogenic gas production with abiotic gas production experiments, it was found that the gas formation significantly affects the gas distribution and resulting degree of saturation. The experimental results and image analysis provide insight in the kinetics of the precipitation and gas formation processes and their resulting distribution and related engineering properties.