Predictive model for the growth of Bacillus sp. in biopolymer solid-free drilling fluids at different pH conditions

Abstract:

Microbially induced calcium carbonate deposition （MICP） technology provides a useful reference for the geological drilling industry to solve the problem of borehole wall instability in fractured formations. Exploring the growth pattern of microorganisms under the environmental conditions of drilling fluids is the primary prerequisite for the successful application of MICP technology to solve borehole wall instability in fractured formations. Therefore， in this study， we examined the growth of Bacillus sp. in XC drilling fluid at pH 7.0， 7.4， 7.8， 8.2， 8.6， 9.0， 9.4， 9.8， and 10.0， analyzed and fitted its growth pattern， and constructed its growth prediction model. The results showed that Bacillus sp. could grow normally under the experimentally set pH conditions. A comprehensive comparison of regression coefficient， mean square error， red pool information criterion， accuracy factor and bias factor of the models showed that the modified Gompertz model was more suitable to describe the growth of Bacillus sp. in XC drilling fluid， and the Arrhenius model was more suitable to describe the influence law of pH on the maximum specific growth rate of Bacillus sp. in XC drilling fluid. The results of the study lay a good theoretical foundation and provide a scientific basis for the successful application of using MICP technology to stabilize the borehole wall of fractured formations.