Gravel pack composition containing gravel and a water-in-oil emulsion including (a) an organic continuous phase comprising 0.1 to 5 vol % of the emulsion of non-ionic or cationic surfactant and 0.25 to 3 vol % of the emulsion of sorbitan ester; (b) a dispersed aqueous phase comprising 0.05 to 3 vol % of the emulsion of a partial ester of a polyol with at least one C6 to C22 fatty acid and at least one of an acid, acid precursor, and a chelating agent; and (c) a density control agent. The fluid can display a delayed break of up to about 72 hours to enable clean-up of mud cake.