Reply  First the tens of thousand more heavy oil than lightr crude is false To get this figure you probably included all organic content in the lithosphere as if there was a remote chance to gzet anything usable from a  km deep shale with  of kerogen You got confused light oil and conventionnal oil what you categorized as lowgrade oil is for a large part not oil at all kerogen   Second there is a important notion you ignored  net energy yeld The vast majority of low grade fossil fuels like deep oil shale would consume more energy to extract than they would give Already the Athabasca oil sands have a selfconsumption of about   that could be reduced to some  with advanced technology The smallsclae oil shale projects that were teste had a nearzero net energy yields  except in estonia but the shales they used were among the richest known  Third extraction rate is as important as reserves Non conventionnal oil biodegraded oil bitumen oil heavier than water is very difficult to take out Kerogen from shale is even worst Even if these ressources are in the trillions of barrels they wont provide much help if we can only get a few million barrels out per day  Fourth nonconventionnal has an high environmental cost CO emeissions on a fullcycle basis from well to end use are much higher There are other problems like the destruction of ecosystems for openpit production of both oil shale of oil sands water use especially for oil shale water pollution disposal of wastes for oil shales These environmental costs would become catastrophic is nonconventional production was to be upscaled to the same range of output than current conventional production