A method of sealing a formation that includes drilling a wellbore through the formation while pumping a non-aqueous based wellbore fluid comprising an encapsulated first component into the wellbore, the non-aqueous based wellbore fluid forming a filter cake on the walls of the wellbore; and adding a second component to the wellbore fluid when fluid losses are registered during drilling, whereby the first and second components react to form a chemical sealing layer in the filter cake is disclosed.