Polymeric and low molecular weight shale inhibitors: A review

Water-based drilling fluids (WBDFs) are widely used for drilling oil and gas wells. Water-based drilling fluids are considered economical and environmentally friendly compared to synthetic and oil-based drilling fluids. Water is one of the major constituents of WBDFs but causes the swelling of clay minerals in wellbore formations. Clay swelling in the wellbore has detrimental impacts on drilling operations and it leads to excessive costs of drilling operations and oil well construction. During drilling operations, the interactions of drilling fluid and clay swelling can be prevented by using various inhibiting agents that reduce the interactions of water contents with the wellbore. To develop high-performance shale inhibitors that can significantly reduce clay swelling, drilling operation costs, and environmental impacts, a significant amount of research on the industrial and academic level has been done. The available literature lacks a comprehensive understanding of polymeric, amine-based, ionic liquids, and surfactant-based shale inhibitors for the oil field applications. This review explains the mechanisms of clay swelling, techniques used for the measurement of clay swelling, and various inhibitors used to prevent clay swelling. Additionally, the effects on the process for various polymer-based inhibitors, nitrogen-based inhibitors, ionic liquids, and surfactants based shale inhibitors have been studied in detail.