The Development of an Alginate Drilling Fluid Treatment Agent for Shale and a Study on the Mechanism of Wellbore Stability Sealing

In order to prevent and control the problem of wellbore instability during the drilling process in shale formations, this study, based on the unique rheological properties, water solubility, and thermal stability of sodium alginate (SA), systematically investigated the rheological properties, filtration properties, and temperature resistance of sodium alginate-based drilling fluids before and after salt contamination. Additionally, it explored the wellbore stability and plugging mechanism of these drilling fluids in shale formations. The research shows that the BF + 0.4 wt% SA system significantly improves the rheological properties of the drilling fluid, effectively reduces the filtration loss, and exhibits good stability under the conditions of salt contamination and a high temperature of 100 °C. Sodium alginate binds to clay particles through hydrogen bonds and ionic bonds, enhancing the hydration and dispersion ability of the particles. The absolute value of its zeta potential reaches 39 mV and 37 mV before and after salt contamination, respectively, which is better than that of the control group, thus improving the colloidal stability of the drilling fluid. At the same time, through the moderate flocculation of clay particles, low-permeability filter cakes with filtration losses of 14 mL and 25 mL before and after salt contamination are formed, realizing a wellbore stability mechanism that combines physical plugging and chemical inhibition.