The Adhesive Strength and Water Resistance Performance of an Improved Sodium-Lithium Silicate Bonding Agent for Enhanced Drilling in Unconsolidated Formations

Summary Water-induced degradation often constrains the use of sodium silicate (SS) as a bonding agent in drilling operations, thereby compromising its long-term adhesive strength. In this study, we introduce an adhesive composed of SS (modulus = 2.0), lithium silicate (LS), and silicon phosphate (SP), capable of binding sand particles together into a cohesive, waterproofing aggregate. The optimal formulation (10% SS, 5% LS, and 0.5% SP) achieved a Brazilian splitting tensile strength of 1.458 MPa under dry conditions, exhibiting 93.7% retention (1.367 ± 0.035 MPa) after 2 hours of water immersion and preserving structural integrity for 48 hours with 72.1% residual strength (1.052 MPa). Microstructural analyses via optical microscope, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) revealed that the interparticle connections were strengthened by rigid bonding bridges and water-resistant films, predominantly composed of amorphous silica. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) results demonstrate that LS increased silica sources and promoted Si-O-Si network formation while confirming lithium ions’ competitive displacement of sodium ions within the silicate gel framework. Through this study, we provide a potential method for improving the stability of unconsolidated formations using a composite silicate binder, offering new insights into the development of chemical bonding agents in complex geological and engineering environments.