GB1480811A - Internally pressurised load supporting mast - Google Patents

Abstract

1480811 Propelling and guiding elevators BAKER OIL TOOLS Inc 23 Aug 1974 37278/74 Heading B8L [Also in Division E1] A workover rig for pulling or snubbing well pipe, e.g. on an offshore platform 13, includes a vertical mast 11 and lift means 24 which are moved up and down the mast 11 by a linear hydraulic actuator 56 acting through a pulley system, the pressure fluid for the actuator 56 passing through the legs of the mast 11 to compensate for the load on the mast. As described the mast 11 consists of front and rear legs 16, 17 and 14, 15 and is pivoted at 19 to a frame 20 mounted on a skid member 12. The mast is raised by piston and cylinder 91 until the front legs 16, 17 rest on pads 22. The front legs 16, 17 are then connected, through frame 110, to the top 130 of the well casing so that loads imposed on the mast are transmitted to the well easing rather than the platform 13. The lift means 24 (Fig. 8) consists of a cross head 25 having rollers 26 which run up and down the front legs 16, 17. The cross head 25 carries a rotary table 33 and a pipe gripping assembly consisting of a slip bowl 37 and a snubber bowl 38. Similar pipe gripping means (not shown) are mounted at the top of the well casing. The cross head 25 is connected to vertical cables by clamps 29, 30. The mast carries crown pulley sheaves 41, 42, equalizer sheave 84, and base pulley sheaves 79, 80. The hydraulic actuator 56 consists of a piston and cylinder device, the piston rod being fixed to the top of the mast, and the cylinder being movable and guided by rollers 70. The cylinder carries pulley sheaves 74, 75, 76, 77. The cable system (Fig. 7) consists of a single cable which is anchored at 89 and passes around sheave 77, then base sheave 79, crown sheave 47, sheave 76 and then over equalizer sheave 84 to the opposite side which is identical to the first side. The lifting means 24 is clamped to the vertical runs of cable between the crown and base pulleys 41, 42 and 79, 80. This arrangement produces a double purchase whereby the stroke of the lifting means 24 is double that of the cylinder 56. The arrangement also allows the pipe to be snubbed into the well. Pressure fluid is supplied to the rod end of cylinder 56 through passages in the front legs 16, 17 and to the head end of cylinder 56 through passages in the rear legs 14, 15, the fluid pressure in legs 14 to 17 compensating for the compressive loads imposed on the legs during operation of the rig. The rig may be used in combination with a pair of winches 180 (Fig. 15) having cables 183, 184 which pass over additional pulleys 188, 189 provided at the top of the mast. The cables 183, 184 carry pipe elevators 190 and are used to transfer pipe between a pipe store and the rig as shown in Fig. 15. Each pipe elevator 190 (Fig. 10) consists of a cylinder 197 having a handle 200 and and axial opening 198 equal to the diameter of the pipe. A recess 199 receives the box end of the pipe to support the pipe.