A system for producing hydrocarbons in situ from a heavy-oil and tar sand fixed bed, hydrocarbon deposit distributed substantially within a porous formation. The system includes at least one injection well and at least one production well drilled into the formation. A heated thermal-energy carrier fluid is circulated into the injection well and through a hydraulic fracture in the formation. The fracture is disposed between the injection well and the production well. The carrier fluid mobilizes hydrocarbons in situ by heating the hydraulic fracture and producing mobilized hydrocarbons through the production well. The hydrocarbons are then divided into at least two fluid fractures having differing chemical compositions.