A method for treating a relatively permeable formation containing heavy hydrocarbons in situ may include providing heat from one or more heat sources to a portion of the formation. The heat may be allowed to transfer from the heat sources to a selected section of the formation. The transferred heat may pyrolyze at least some hydrocarbons within the selected section. A temperature proximate a selected portion of a heater well may be selectively limited to inhibit coke formation at or near the selected portion. A mixture of at least some hydrocarbons may be produced through the selected portion of the heater well.