A method for producing hydrocarbons from subsurface formations at
different depths is first provided. In one aspect, the method includes
the step of heating organic-rich rock, in situ, within a subsurface
formation at a first depth. The result of the heating step is that at
least a portion of the organic-rich rock is pyrolyzed into hydrocarbon
fluids. Preferably, the organic-rich rock of the subsurface formation of
the first depth is oil shale. The method also includes providing at least
one substantially unheated zone within the formation of the first depth.
In this way, the organic-rich rock in that zone is left substantially
unpyrolyzed. The method further includes drilling at least one production
well through the unheated zone, and completing the at least one
production well in a subsurface formation at a second depth that is
deeper than the first depth. Thereafter, hydrocarbon fluids are produced
through the at least one production well.