Growth Kinetics of Bacillus pasteurii in Solid-Free Drilling Fluids

Area of Science:

• Geology and Petroleum Engineering
• Microbiology
• Materials Science

Background:

• Well wall instability in broken strata is a significant drilling challenge.
• Microbially induced calcite precipitation (MICP) offers a novel solution for wellbore integrity.
• Understanding microbial growth in drilling fluids is crucial for MICP application.

Purpose of the Study:

• To evaluate the growth of *Bacillus pasteurii* in various drilling fluid formulations.
• To develop a predictive model for microbial growth in drilling fluids.
• To identify optimal drilling fluid compositions for microbial activity.

Main Methods:

• Experimental analysis of *Bacillus pasteurii* growth in single and mixed-agent drilling fluids.
• Theoretical modeling using a modified Gompertz model to fit experimental data.
• Statistical evaluation of model fit using mean square error, bias, and accuracy factors.

Main Results:

• The modified Gompertz model accurately predicted *Bacillus pasteurii* growth in drilling fluids.
• Optimal single-agent fluid for growth: XC.
• Optimal two-agent fluids: XC and XC/PAC-LV.
• Optimal three-agent fluid: FA367, XC, and K-PAM.

Conclusions:

• The study provides a foundation for developing microbial drilling fluids for broken strata.
• Specific drilling fluid formulations support *Bacillus pasteurii* growth.
• Predictive modeling aids in optimizing microbial drilling fluid design.