Multi-branch geothermal well system and construction method

A multi-branch geothermal well system comprises an overground heat exchange unit and an underground heat exchange unit, the underground heat exchange unit comprises a geothermal well and a heat exchange pipe, the heat exchange pipe is arranged in the heat exchange well and communicated with the overground heat exchange unit, the geothermal well comprises a main well and a plurality of branch wells, the main well is a vertical well, and the branch wells are communicated with the ground heat exchange unit. At least one well cementation sleeve is arranged on the inner wall of the main well, the fixed sleeve extends in the length direction of the main well, the open hole part of the main well and/or the fixed sleeve are/is provided with a plurality of branch wells which are obliquely arranged downwards, heat exchange pipes are arranged in the branch wells and the main well, and plugging layers are arranged at the joints of the heat exchange pipes and the branch wells and the main well. The heat exchange pipe is a