Single-stage well cementation anti-upside-down high-temperature large-temperature-difference cement paste system

The invention provides a single-stage well cementation anti-upside-down high-temperature large-temperature-difference cement paste system. The concrete is prepared from the following components in parts by weight: 100 parts of cement, 0-20 parts of superfine cement, 40-45 parts of silicon powder, 0-100 parts of a weighting agent, 0-15 parts of micro silicon, 0-4 parts of an anti-channeling agent, 0-0.5 part of a separant, 0-3 parts of an elastic-plastic agent, 6-8 parts of an anti-upside-down reinforcing agent, 6-8 parts of a high slow fluid loss agent, 2-3 parts of a drag reducer, 0.5-2 parts of a retarder, 1 part of a defoaming agent, 1 part of a separant, 2-3 parts of an expanding agent and 60-90 parts of water. The technical problems that in the prior art, the strength of the top of cement paste returned to the ground in a temperature-crossing area of a polymer cement paste system cannot meet the well cementation requirement of an ultra-deep and long cementation section, and the strength of top cement sto