Well cementation method for horizontal well

The invention provides a well cementation method for a horizontal well, and belongs to the technical field of oil exploitation. The well cementation method of the horizontal well comprises the steps that a pipe string is tripped into a preset position in a shaft, and the pipe string comprises a float shoe, a first casing pipe, a float collar, an air casing pipe, a float coupling, a second casing pipe, a packer, a grading collar and a third casing pipe which are sequentially connected; the floating coupling is opened; air in the shaft and air in the pipe string are exhausted; a ball is thrown into the pipe string, and the pipe string is plugged between the packer and the air sleeve; pressure is built in the pipe string, so that the packer is set; continuing to build the pressure in the pipe string until the grading hoop is opened; and cement paste is injected into the third casing pipe and replaced, and half-pass well cementation is completed. The floating casing running technology and the half-process well ce