A Copolymer as Asphalt Replacement: Enhancing the High-Temperature Performance of Oil-Based Drilling Fluids

Oil-based drilling fluids (OBDFs) are widely employed in deep oil and gas drilling operations. Asphalt materials, as key additives for OBDFs, suffer from high toxicity and poor environmental compatibility, limiting their sustainable application. To address this issue and enhance the comprehensive performance of OBDFs with reduced environmental risks, a polymer (LDBA) was synthesized via suspension polymerization using isobutyl acrylate (BA), acrylic acid (AA), lauryl methacrylate (LMA), and diacetone acrylamide (DAAM) as monomers. The performance of LDBA was evaluated by testing the high-temperature and high-pressure filtration loss (FLHTHP), viscosity, and demulsification voltage (ES) of LDBA-containing OBDFs. Results showed that LDBA outperformed traditional acrylic resin and asphalt additives. At an optimal dosage, LDBA significantly reduced the FLHTHP of OBDFs after high-temperature aging while maintaining excellent rheological and emulsion stability. It is worth noting that its biological toxicity test (EC50) is 307420 mg/L, far exceeding the nontoxic threshold, confirming its excellent environmental compatibility. To elucidate its working mechanism, systematic analyses of the oil absorption behavior and filter cake microstructure were performed. The key mechanism encompasses the intermolecular interactions of LDBA, its robust thermal stability inherent to the molecular structure coupled with stable dispersion in the oil phase, oil absorption-induced swelling to plug the pores and fractures of the filter cake, and the adaptive optimization of filter cake structure; these effects collectively reduce filtration loss and enhance the stability of OBDFs. This study provides a green and high-performance alternative to asphalt-based additives, thereby facilitating sustainable development of deep drilling operations.