A method for treating a relatively permeable formation containing heavy hydrocarbons in situ may include providing heat from a first set of heat sources to a first section of the formation. The heat provided to the first section may pyrolyze at least some hydrocarbons in the first section. Heat may also be provided from a second set of heat sources to a second section of the formation. The heat provided to the second section may mobilize at least some hydrocarbons in the second section. A portion of the hydrocarbons from the second section may be induced to flow into the first section. A mixture of hydrocarbons may be produced from the formation. The produced mixture may include at least some pyrolyzed hydrocarbons.