Abstract
In the geological core drilling industry, simple and low-cost drilling fluid formulations are required that are easy to apply and maintain. Currently, drilling fluid systems with simple formulations generally exhibit poor performance and do not satisfy the requirements of complex formations. The application of powder surface modification technology has been extensively investigated in several fields; however, few are the studies focusing on the modification of bentonite. Consequently, in this study, based on the surface modification technology of powders, bentonite is modified using the modifiers ZJ-1 and ZJ-2, giving it the characteristic of "one additive with multiple functions". This allows the construction of a new type of drilling fluid system with a simple formulation (water + modified bentonite), excellent performance, and easy application and maintenance. First, a new composite modification method named the dissolution and extrusion composite modification method was proposed, and the dosage of the modifier and the optimal ratio of each modifier were determined experimentally. Second, orthogonal design experiments were conducted to determine the optimal preparation conditions based on the rheological properties of the drilling fluid, dynamic plastic ratio, and filtration loss. Subsequently, the performance of the modified bentonite drilling fluid was analyzed by comparing it to that of a regular bentonite drilling fluid. Finally, the modification mechanism of bentonite was analyzed using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). It was revealed that a total modifier dosage of 2% and a ratio of ZJ-1 to ZJ-2 of 1.5:0.5 afforded a modified bentonite drilling fluid with significantly enhanced performance compared to a regular bentonite drilling fluid. The modified bentonite exhibited a filtration loss of 7.5 mL, funnel viscosity of 51.5 s, static shear force of 2.5 Pa, dynamic shear force of 9.198 Pa, apparent viscosity of 29 mPa·s, and plastic viscosity of 20 mPa·s. The experimental repeatability was good, and the optimal preparation conditions for modified bentonite involved a reaction time of 10 h, a reaction temperature of 100 °C, and a mechanical pressure of 0.5 MPa. Microscopic analysis showed that the modifiers were incorporated into bentonite through intercalation and surface adsorption and that the modified bentonite can form a dense filter cake. Our study provides a new drilling fluid solution for the geological core drilling industry, effectively promoting the advancement of drilling fluid technologies.