Disclosed herein is a copolymer concentrate in a bio-solvent that can be further diluted into a slurry composition. The bio-solvent facilitates the formation of a viscosified base fluid with the mixing being carried out in a short period of time and at ambient, providing a free flowing, pumpable, and dispersible slurry. The slurry is characterized as having excellent stability, maintaining suspension over a wide range of temperatures. In embodiments, the bio-solvent is selected from terpene and terpene-derivative-containing solvents, fatty acid alkyl esters, and mixtures thereof. The bio-solvent can be first mixed with a styrenic diblock copolymer to form a concentrate prior mixing with a hydrocarbon solvent, forming a viscosified base fluid for subsequent mixing with a water-soluble polymer to form the slurry. The bio-solvent can also be used to dilute the hydrocarbon solvent, prior to mixing with the styrenic diblock copolymer to form the viscosified base fluid.