**2. History of clay-fluid interactions**

Trends of research on interactions between formation clay minerals and fluids over the years have largely been determined by the exigencies of the petroleum industry. The drive for this is the need for in-depth understanding of reactions in order to characterise reservoirs and cap rocks, as close as possible to *in situ* conditions. Summary of research trajectories in major periods is explained in the following paragraphs and captured in **Figure 1**.
