Enhancing wellbore cement integrity with microbially induced calcite precipitation (MICP): A field scale demonstration

Abstract

The presence of delaminations, apertures, fractures, voids and other unrestricted flow channels in the wellbore environment substantially reduces wellbore integrity. Compromised cement may cause a loss of zonal isolation leading to deleterious flow of fluids between zones or to the surface with multiple potential negative impacts including: loss of resource production, reduction of sweep efficiency in EOR operations, and regulatory non-compliance. One potential solution to enhance wellbore integrity is microbially induced calcite precipitation (MICP) to plug preferential flow pathways. MICP is promoted with micrometer-sized organisms and low viscosity (aqueous) solutions thereby facilitating fluid transport into small aperture, potentially tortuous leakage flow paths within the cement column. In this study, MICP treatment of compromised wellbore cement was demonstrated at a depth interval of 310.0–310.57 m (1017–1019 feet) below ground surface (bgs) using conventional oil field subsurface fluid delivery technologies (packer, tubing string, and a slickline deployed bailer). After 25 urea/calcium solution and 10 microbial (Sporosarcina pasteurii) suspension injections, injectivity was reduced from the initial 0.29 cubic meters per hour (m3/h) (1.28 gallons per minute (gpm)) to less than 0.011 m3/h (0.05 gpm). The flow rate was decreased while maintaining surface pumping pressure below a maximum pressure of 81.6 bar (1200 psi) to minimize the potential for fracturing a shale formation dominant in this interval. The pressure decay immediately after each injection ceased decreased after MICP treatment. Comparison of pre- and post-test cement evaluation logs revealed substantial deposition of precipitated solids along the original flow channel. This study suggests MICP is a promising tool for enhancing wellbore cement integrity.