Growth Kinetic Models of Sporosarcina pasteurii in PAC Seawater-Based Drilling Fluid Under Low-Temperature Conditions

Marine natural gas hydrates, as a highly promising green energy source, are prone to wellbore instability during drilling and extraction due to their occurrence forms and the weakly cemented characteristics of the reservoir. Enhancing reservoir cementation and improving the strength of the wellbore surrounding rock are critical to overcoming this instability challenge. Microbially induced calcium carbonate precipitation (MICP) technology offers a novel approach to address this issue; however, elucidating the growth patterns of microorganisms in low-temperature seawater-based drilling fluids is a prerequisite for applying MICP to improve the wellbore stability of marine natural gas hydrate reservoirs. In this study, the growth of Sporosarcina pasteurii was monitored in polyanionic cellulose (PAC) seawater-based drilling fluid at 10, 8, 6, and 4 ℃, and the growth data were fitted to construct a predictive model. The results indicate that both the seawater environment and low temperatures inhibit the growth of S. pasteurii, prolonging its lag phase, and the bacterial concentration decreases with decreasing temperature. Notably, under 4–10 ℃ conditions, the growth of S. pasteurii in PAC seawater-based drilling fluid was superior to that in natural seawater. Model evaluation showed that, in the low-temperature PAC seawater-based drilling fluid system, the modified Logistic model is more suitable as a primary growth predictive model for S. pasteurii, while the square-root model is more appropriate as a secondary growth predictive model. These findings provide a critical theoretical foundation and scientific basis for applying MICP technology to mitigate wellbore instability during the drilling of marine natural gas hydrates.