A method for treating a relatively low permeability 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 mixture of hydrocarbons may be
produced from the selected section. In certain embodiments, one or more heat sources
may be placed in an uncased wellbore.