Functional groups optimization at molecular-scale to improve polyamine treatment agent performance on sodium bentonite surface hydration inhibition under high-temperature/high-pressure failure

Application of water-based drilling mud systems poses challenges of wellbore instability due to overhydration and dispersion of contained Na-bentonite/montmorillonite (Na-Mnt), which readily experience hydration expansion, dispersing into the drilling fluids, reducing their performance. Alkylamine-organoclays' inhibition ability of Na-Mnt surface hydration weakens under deeper wellbore harsh conditions, degrading the drilling fluid performance. Functional groups are indispensable for the performance of organic inhibitors, thus keen selection of functional groups is necessary to improve inhibition action. The effect of aminomethyl, hydroxymethyl, ethyl, and N,N-dimethylacetamidomethyl functional groups on the inhibition of heptane-1,7-diamine and intermolecular interactions in the Mnt outer surface hydration system were investigated under high-temperature/high-pressure (HT/HP) using molecular dynamics simulation. Adsorption conformation, H-bond formation, hydration analysis, self-diffusivity, and interaction energy parameters were scrutinised. N,N-dimethylacetamidomethyl showed the best surface hydration inhibition improvement. HT/HP significantly reduced the inhibition effectiveness. This study conceptualizes the development of alkylamine-bentonite-based drilling fluid additives for deep and ultra-deep wellbore stabilisation.