Biofilm-induced calcium carbonate precipitation : application in the subsurface

Abstract

Subsurface leakage mitigation strategies using ureolytic biofilm- or microbially-induced calcium carbonate precipitation (MICP) have been investigated for sealing high permeability or fractured regions. In the subsurface, this technology may help reduce unwanted preferential flow pathways thereby improving the storage security of geologically-stored carbon dioxide or sealing fractures caused by hydraulic fracturing. MICP has been researched for other applications, such as consolidating porous materials, improving construction materials and remediating environmental concerns. Injection strategies to control saturation conditions and region-specific precipitation were developed in sand-filled columns. Sporosarcina pasteurii biofilms were established and calcium and urea solutions were injected to promote mineralization. These injection strategies resulted in (1) promoting homogeneous distribution of CaCO 3 along the flow path, (2) minimizing near-injection point plugging, and (3) promoting efficient precipitation by reviving ureolytic activity. Additionally, a Darcy-scale model was calibrated and used to predict experimental results. The developed injection strategies were used to repeatedly seal a hydraulically fractured, 74 cm diameter Boyles Sandstone core under ambient pressures. To study meso-scale samples under relevant subsurface pressure conditions, a high pressure test vessel, rated to pressures of 96 bar, was developed. The hydraulically fractured sandstone core was loaded into the vessel and treated with MICP at 44 bar of confining pressure. After treatment, the permeability was reduced and the sandstone core withstood three times higher well bore pressures before re-fracturing compared to before MICP treatment. Additionally, MICP was promoted in three 2.5 cm diameter Berea Sandstone cores under 76 bar of pressure. The cores' permeabilities were reduced and their minimum capillary displacement pressures (MCDP) were increased. Exposure of the biomineralized cores to 24 hours of supercritical CO 2 did not negatively impact the permeability or MCDP achieved after mineralization. These studies suggest MICP may potentially seal and strengthen subsurface high permeability regions or fractures with the advantage that MICP technologies use low-viscosity fluids to penetrate small aperture pores that may not be reachable by traditional cement-based sealing technologies. These studies also point to the need for further research and development activities, particularly under subsurface relevant pressure conditions.