Microbiological mineralization for self-healing cement sheath in oil and gas wells: A study on the integrity and sealing mechanisms of interface cracks

Cementing technology is crucial for wellbore stability in oil and gas exploitation. However, stratum fluid erosion causes micro-cracks at the cementing secondary interface, reducing extraction efficiency and posing safety risks. This study explores the effectiveness of microbiologically induced mineralization self-healing technology in enhancing cement sheath integrity and sealing, using the Chun Guang Oilfield’s cementing failure as a backdrop. Microbiological cementing simulation experiments were conducted to study the self-healing mechanisms of secondary interface cement under microbial mineralization. The results show significant improvements due to microbial-induced calcium carbonate precipitation (MICP). Under MICP, Type B specimens reached 7.5 MPa after 140 days, a 25 % increase compared to conventional methods (6 MPa). For Type A specimens in the microbial groups, strength rose from 0.5 MPa at 28 days to 0.7 MPa at 140 days, while the control groups had limited growth (from 0.3 MPa to 0.45 MPa). The microbial groups achieved an ultra-low permeability of 0.005 mD for Type A specimens. Fractured specimens in the microbial groups had a 60–75 % greater permeability reduction than the control groups. Pore structure parameters also improved: porosity decreased from 4.2 % to 3.2 % after 140 days, pore sphericity declined by 17.3 % (from 0.52 to 0.43), and the pore throat ratio increased from 1.53 to 1.71. Moreover, MICP led to a 98.5 % reduction in fracture volume in Type B specimens (from 0.41 % to 0.03 %) after 140 days of curing, better than the 90.2 % reduction in the control groups. The precipitate volume fraction grew linearly from 0.001 % to 0.023 %, indicating sustained microbial activity. Overall, MICP significantly enhances interface cementation properties by improving the internal pore structure, especially after long-term curing. It offers a promising solution for improving cementing quality and preventing stratum fluid intrusion. Microbiological mineralization mainly occurs at cracks, aiding in crack repair. This research provides new insights into improving the cement sheath-formation interface and theoretical support for downhole microbiological self- healing cementing technology. • Scalable MICP technology for interfacial strengthening in cement sheath-formation interfaces was demonstrated. • Quantitative multi-parameter characterization of pore and crack structure evolution under microbial remediation was studied. • The long-term self-repair capabilities through continuous carbonate precipitation were validated. • The mechanism of self-healing process of interface cracks was proposed.