Abstract: Methods disclosed for reducing the loss of a circulating fluid in a wellbore to an adjacent subterranean formation during a wellbore operation include coiled tubing milling, cleanout and gravel-packing operations. The methods include placing, either before, during, or before and during the operation, a first acid precursor material, and optionally fibers, in contact with the subterranean formation adjacent to the wellbore to at least partially form a temporary reservoir barrier and reduce hydraulic conductivity between the wellbore and the subterranean formation. The first acid precursor material has a first average particle size of about 3000 microns or less.