Staged cementing device and staged cementing method

A staged cementing device (10), comprising:

• a body (100) having an inner chamber (110), a circulating opening (120) extending through a wall of the body, and a liquid inlet recess (130) open to the inner chamber and formed on the wall of the body;
• an opening assembly (300) arranged in the body, the opening assembly comprising an opening sleeve (310) and an opening seat (320) located in the opening sleeve (310), wherein in an initial state, the opening sleeve (310) is connected with the body (100) through a first shear pin (180) and covers the circulating opening (120), and the opening seat (320) is connected with the opening sleeve (310) through a second shear pin (182) and covers the liquid inlet recess (130);
• and
• a packer (200), wherein the packer (200) comprises a packing valve body (210) connected with a downstream end of the body, and a packer rubber (220) arranged downstream of the packing valve body, the packing valve body (19) comprises a flow channel (230) in communication with the liquid inlet recess (130), and the packer rubber (220) comprises a liquid reservoir (240) in communication with the flow channel (230), wherein the liquid reservoir (240) contains an accelerant for a swelling fluid,
• wherein the second shear pin (182) is configured to be sheared off in response to a primary pressure build-up in the body (100), causing the opening seat (320) to move downward to open the liquid inlet recess (130) so that the swelling fluid in the inner chamber (110) of the body (100) enters the liquid reservoir (240) through the liquid inlet recess (130) and the flow channel (230) and reacts with the accelerant in the liquid reservoir (240).