Lignin-based adhesives as wellbore strengthening agents in water-based drilling fluids

The efficient development of oil and gas resources in fractured reservoirs has long been constrained by complex geological structures, drilling fluid invasion, and wellbore instability, among which wellbore instability represents a critical technical bottleneck affecting safe drilling operations and efficient resource exploitation. To address this challenge, an environmentally friendly lignin-based wellbore strengthening agent (LSA) was developed in this study through the condensation reaction of renewable dealkalized lignin and furfural in a deep eutectic solvent system and applied to fractured shale stabilization in water-based drilling fluids. Experimental results show that LSA not only effectively improves the rheological properties and filtration control performance of drilling fluids, thereby enhancing cuttings-carrying capacity and wellbore protection, but also penetrates shale fractures and establishes strong physicochemical adsorption on rock surfaces. Based on adsorption tests, dynamic interfacial adhesion measurements, zeta potential analysis, SEM observations, and FTIR characterization, LSA is demonstrated to form a dense and stable cementing interfacial layer on shale surfaces through interfacial adsorption, fracture filling, and thermally driven curing. This process significantly enhances the overall bonding strength and failure resistance of fractured rock masses. This study provides a new strategy and theoretical basis for the development of high-performance and sustainable wellbore-strengthening materials for water-based drilling fluids. The innovation of this work lies in the use of a deep eutectic solvent to promote the reaction between lignin and furfural, thereby constructing a green functional material with excellent thermal stability, strong adhesion, and effective fracture-cementing capability. This strategy enables the synergistic integration of industrial lignin valorization and wellbore stability enhancement. Download: Download high-res image (236KB) Download: Download full-size image