Laboratory studies and field case histories are presented that demonstrate enhanced well productivity when selection and formulation of solids-free, high density completion fluids are optimized prior to field use. Results of return permeability studies and compatibility tests between completion fluids and formation fluids are presented. These results illustrate the tendency for high density completion fluids to form stable emulsions with certain crude oils. Studies supporting the treatment of these fluids with non-emulsifiers, surface tension reducing surfactants or mutual solvents to reduce formation damage are discussed. Preliminary data describing unique chemistry of calcium chloride, calcium bromide and zinc bromide solutions are provided. These properties influence recovery of high density fluids from oil or gas formations.