Energy recovery medium (150) for insertion into a ground hole (200) in a ground (202) comprising a recoverable energy carrying medium (270), wherein the energy recovery medium (150) comprises a base liquid (100),a carbohydrate-based thickener (102) mixed in the base liquid (100), a salt (104) dissolved in the base liquid (100) and configured for increasing a density of the base liquid (100), and proppant particles (106) dispersed within the mixture of the base liquid (100), the thickener (102) and the salt (104).