The invention discloses a method for staged fracturing of a well cementation
casing string and a tool for the method. The method and the tool are particularly suitable for implementation of staged fracturing and matched well completion after well cementation in oil-gas
well engineering. The method is characterized in that hydraulic reducing ball seat sleeve sliding sleeve switch tools (3) are connected in series in a
casing string (2) to descend a well, when the tools go down to the designed depth,
cement paste is pumped into the well for well cementation, a sleeve is fixed in a
ground layer (1), after well cementation, the sealing sleeves of all the hydraulic reducing ball seat sleeve sliding sleeve switch tools (3) are opened in sequence by colliding rubber plugs,
cement paste on the inner wall of the
casing string is removed, the pressure is built, the hydraulic reducing ball seat sleeve sliding sleeve switch tools (3) seal ball seats for
diameter change, and the diameters of the ball seats are increased from the bottom of the well to the top in sequence, so that ball throwing staged fracturing operation can be carried out. Compared with a similar technology, the method and the tool have the benefits that before colliding, the casing string has a drift
diameter which is the same in
diameter so as to ensure that the well cementation colliding rubber plugs descend smoothly;
cement takes the place of
cement paste in the clean casing string, so that the success rate of colliding is high.