Coupled Computational and Laboratory Investigations of Interface Interactions between Binary Polymers, Hydroxypropyl Guar, and Potassium Formate for Crosslinked Hydraulic Fracturing Fluids

Abstract

Summary Guar gum is an economically and environmentally important material. However, reduced rheological properties of hydroxypropyl guar (HPG) in saline conditions of potassium formate (PF) impeded its hydraulic fracturing (HF) applications. In this study, we coupled molecular dynamics simulation and bench experiments to design binary polymers that can be used to mitigate the reduced viscosity of the HPG-PF system and investigate the relevant physiochemical processes in the fluid. The modeling showed that binary polymer P(AM-AA) with acrylamide (AM) and acrylic acid (AA) monomers had the highest ability to bind water molecules in the HPG-PF solution among four representative binary polymers. Multiple analyses showed that adding P(AM-AA) decreased the number of formate ions around the HPG molecules, bonded with the HPG molecule through hydrogen bonds, and mitigated the coiling of the HPG molecular chain in PF solutions. Further experiments and characterization at the macro- and microscale showed that adding P(AM-AA) indeed improved the viscosity, microrheology, viscoelasticity, and thermal tolerance [>120°C (248°F)] of the HPG-PF solution (1.47 g/cm3) and its associated gel system. Our study indicates the potential application of HPG-PF-P(AM-AA) weighting crosslinked HF fluids (HFFs) for wells with stringent wellbore pressure constraints. It also highlights the significant role of binary polymers in enhancing rheological properties in gel-based crosslinked HFF and addressing complex fluid interface interactions through molecular dynamics simulations.