A composition and method are disclosed. The composition includes a carrier fluid and a solids mixture combined to form a slurry, wherein the solids mixture comprises a plurality of volume-averaged particle size distribution (PSD) modes, wherein a first PSD mode comprises solids having a volume-average median size at least three times larger than the volume-average median size of a second PSD mode such that a packed volume fraction of the solids mixture exceeds 0.75, and wherein the solids mixture comprises a degradable material and includes a reactive solid. The method includes circulating the slurry through a wellbore to form a pack in a fracture and/or a screen-wellbore annulus; degrading the degradable material to increase porosity and permeability of the pack; and producing a reservoir fluid through the permeable pack.