**1. Introduction**

Clay minerals interactions with fluids have gained attention in the petroleum industry because of their presence in source rocks, reservoir rocks and seal rocks in petroleum systems. In conventional reservoirs, interactions between clay minerals and fluids have been studied in relation to wellbore integrity and fines migration during production. The inception of enhanced oil and gas recovery, hydraulic fracturing and carbon storage technologies, highlighted knowledge gaps in terms of interactions between clays and fluids injected into the subsurface. Research efforts are focused to understand the impact of clay-fluid reactions geochemistry on shale geomechanics, and deciphering the mechanisms that drive these interactions in order to optimise various technologies adopted by the industry.

In retrospect, studies on interactions between clay minerals and formation fluids have been going on in the petroleum industry well before introduction of the advanced technologies alluded to above. These studies were mainly focused on the relationship between clay minerals interactions with formation fluids during formation, migration and deposition of hydrocarbons. For example, Drits et al. [1] studied clay mineral-fluid interactions in order to gain insight into transformation processes in clay minerals during generation and migration of hydrocarbons.

This review seeks to present a concise overview of published studies on interactions between clay minerals and various fluids in the subsurface with particular emphasis on hydraulic fracturing fluids. Reaction mechanisms as well as geochemical and geomechanical impacts are assessed.
