Nitrogen injection thermal recovery system for oil shale

The invention relates to an oil shale nitrogen injection thermal recovery system which comprises an underground heating device, an underground oil recovery device and a ground treatment device, the underground heating device comprises a first heat insulation pipe and a nitrogen generation device, an igniter is arranged on the first heat insulation pipe, and a nitrogen output port of the nitrogen generation device is communicated with the interior of the first heat insulation pipe; an air injection hole is formed in the bottom of the first heat-insulating pipe; the underground oil production device comprises a second heat insulation pipe, an oil well pump is arranged on the second heat insulation pipe, and the production well is communicated with the heat injection well through formation pores and cracks; the ground treatment device comprises a first-stage oil-gas separation device and a second-stage oil-gas separation device which are connected with each other, a liquid inlet of the first-stage oil-gas separa