Patent ID: 6343892
Filing Date: 2002-02-05
Classification: E21B

Abstract:
Derrick (12), comprising A number of hydraulic cylinders (42a,42b,42c) arranged in groups (42) having pistons and associated extendible piston rods for axial movement of a drill stem (13) in the derrick (12), where the piston rods at their upper ends are mutually rigidly connected to each other by a bridge portion (45â€²), characterised in thatthe derrick (12), in addition to the first-mentioned group (42) of hydraulic cylinders (42a,42b,42c), comprises additional groups (43,44) of hydraulic cylinders (43a,43b,43c44a,44b,44c) arranged over each other having respective piston rods connected in upper bridge portions (45â€²,45â€³, 45â€²â€³), each group (43,44) of the above standing cylinders (43a,43b,43c; 44a,44b,44c) being carried by the bridge portion of the group standing below; that each group (42,43,44) of cylinders (42a,42b,42c;43a,43b,43c; 44a,44b,44c) is arranged around a middle space for the drill stem (13), and the derrick carries arrangements (40) for rotation of the drill-stem (13), said arrangements (40) being releasably fixed to the bridge portion (45â€²â€³) for the uppermost group of pistons (44a-44c).