A patching construction method using a hydraulic variable-grade expansion tool for blocking during drilling, the variable-grade expansion tool comprising a conversion joint (1), a supporting central pipe (2), a supporting ring (3), an expansion pipe (4), pressure gradient piston subs (5), double female thread connection subs (6), T-shaped limiting subs (7), a tapered centering sub (8), double male thread central shafts (9), split supporting subs (10), an expansion cone (11), a piston sub with male and female threads (12), a T-shaped ball compressor (13), a lower U-shaped pressing sleeve (14), a ball-seat fixing sleeve (15), a reciprocating spring (16), a sealing ball seat (17), a sealing ball (18), a tapered guide sub (19), a first O-ring (20), a second O-ring (21), a third O-ring (23), a fourth O-ring (24) and a fifth O-ring (28);
- wherein one end of the conversion joint (1) is connected to a tubing string and an other end of the conversion joint (1) is connected to one end of the supporting central pipe (2) via threads, and the first O-ring (20) is provided between the conversion joint (1) and the supporting central pipe (2);
- the supporting ring (3) is connected to the supporting central pipe (2) via threads, and is in a clearance fit with the expansion pipe (4);
- an other end of the supporting central pipe (2) is connected to one end of one of the double female thread connection subs (6) which is adjacent thereto via threads;
- each of the pressure gradient piston subs (5) is connected to a corresponding one of the T-shaped limiting subs (7) via threads;
- the tapered centering sub (8), the expansion cone (11) and the split supporting subs (10) are each in a clearance fit with a corresponding one of the double male thread central shafts (9);
- a female thread end of the piston sub with male and female threads (12) is connected to one end of one of the double male thread central shafts (9) which is adjacent thereto via threads, and the fourth O-ring (24) is provided therebetween;
- the ball-seat fixing sleeve (15) is connected to a male thread end of the piston sub with male and female threads (12) via threads;
- and the tapered guide sub (19) is connected to one end of one of the pressure gradient piston subs (5) which is adjacent thereto via threads;
- wherein the method comprises:
- connecting the conversion joint (1) to the tubing string placing the variable-grade expansion tool to an expansion position;
- securing the tubing string on ground;
- pressuring drilling fluid by a pressure pump on the ground, enabling the drilling fluid to reach inner holes of the supporting central pipe (2) and the double male thread central shafts (9) through an inner hole of the tubing string, and enter each of pressure chambers which comprises a first pressure chamber (22), a second pressure chamber (25), a third pressure chamber (26) and a fourth pressure chamber (27) through circumferential holes of a corresponding one of the double male thread central shafts (9), enabling the drilling fluid with high pressure to push each of the pressure gradient piston subs (5) to move axially, and driving the expansion cone (11) to expand the expansion pipe (4);
- pushing the upper sealing ball (18) up by the tapered guide sub (19), compressing the reciprocating spring (16), enabling the internal pressure of the variable-grade expansion tool to decrease sharply;
- turning off the pressure pump on the ground, lifting the tubing string for one stroke, enabling the reciprocating spring (16) to be released, and pressing the sealing ball (18) downwards by the T-shaped ball compressor (13), achieving a seal by matching the sealing ball (18) with the sealing ball seat (17);
- repeating above-mentioned operations until completing a expansion operation;
- enabling positions of the tapered centering sub (8), the split supporting subs (10) and the expansion cone (11) to be exchanged so as to realize a front placement, a middle placement or a rear placement of the variable-grade expansion tool;
- and enabling a patching construction of an open hole and a casing damage well.