Methods of servicing a wellbore include generating gas in a plugging composition in situ within a permeable zone in the wellbore, thereby improving the ability of the plugging composition to seal the permeable zone. The gas may be generated via a chemical reaction by, for example, introducing first and second reactants to the plugging composition that can react at ambient temperatures in the wellbore. In an embodiment, the first and second reactants are concurrently pumped into the wellbore via separate flow paths within two concentric conduits to the permeable zone where they are allowed to contact each other in the presence of the plugging composition. In another embodiment, the first reactant, the second reactant, and a retarder for slowing the reaction between the two reactants are concurrently pumped to the permeable zone. In yet another embodiment, one of the reactants is encapsulated to delay a reaction between the two reactants.