Alkali-Resistant Domestication of Bacillus pasteurii and Its Growth Kinetics in Sodium Carboxymethyl Cellulose Solid-Free Drilling Fluids

Abstract

Microbially induced calcium carbonate precipitation (MICP) provides a novel approach for use in addressing the instabilities of borehole walls comprising broken formations, but the highly alkaline environments of drilling fluids are unfavorable for microbial growth. Therefore, this study investigated the alkaliresistant domestication of Bacillus pasteurii commonly used in MICP. Using gradient domestication, B. pasteurii was domesticated under different pH conditions (pH 8.0, 9.0, 10.0, and 11.0) in sodium carboxymethyl cellulose solid-free drilling fluids. Its growth patterns and variations in urease activity were analyzed to assess the effectiveness of domestication. The Gompertz and logistic models were used to fit the growth patterns of B. pasteurii under different pH conditions, and growth kinetic models were constructed based on the mean square error, Akaike information criterion, and coefficient of determination. The bacterial concentration and urease activity of B. pasteurii were enhanced after alkali-resistant gradient domestication. The Gompertz model accurately described the growth patterns of B. pasteurii after gradient domestication at pH 8.0, 10.0, and 11.0, whereas the logistic model accurately described the growth pattern after gradient domestication at pH 9.0. This study provides scientific evidence and a theoretical basis for the use of B. pasteurii in maintaining the stabilities of borehole walls comprising broken formations.