Patent GB-1362554-A (GB)
Title: Drilling apparatus
IPC: E21B3/02
Filed: 1971-09-16
Abstract: 1362554 Boring earth &c ROBBINS CO 16 Sept 1971 [24 Sept 1970] 43262/71 Heading E1F The threaded connection between the upper and next lower lengths of a drill string 100 supported by, a rotary head 60 is loosened by gripping the part 104 of the next lower length, to prevent rotation and arial movement of the string, coupling the part 104 of the upper length to the head by means 116, and rotating the head, the head being supported to accommodate thread travel at the loosened joint. A base plate 12 carries guide columns 18 connected by a frame 20 and a cross frame 22 sliding along the columns supports a gear casing 30, the gears being driven by motors 38 The cross frame is moved along the columns by three rams 41 connected by a frame 52 and each having a cylinder 42 secured to the cross frame and a piston secured to the baseplate. The gears drive a rotary housing 54 driving the head 60 by means of a splined connection. The head which is connected to the drill string has a support stem 66 connected by a swivel 68 to a linear motor 76 which is mounted on the frame 52 and counterbalances the weight of the head and drill string. The linear motor is linked with a variable voltage transformer or variable resistor connected in a circuit to give an indication of the position of the head. Drilling fluid supplied to the swivel passes down a passage 78 in the stem to the head and drill string. The drill string is built up of lengths 98 each comprising a section 102 and a sub 104, the threaded joint between a sub and a section being secured against separation by an epoxy bonding agent or by the thread design. Each sub has recesses 108, shoulders 110 and flats 112 (Fig. 11) for engagement by wrenches. The housing 54 has an extension 114 carrying the means 116 (a break-out wrench). The wrench 116 has three jaws 126 (Fig. 9) pivoted about pins 128 on a carrier 118 by linear motors 130. When the jaws are swung inwards to engage the sub they form a ring; compression loads being transferred from one jaw to the next. When the wrench 116 is positioned about a sub and rotated anticlockwise with the jaws 126 swung inwards to engage the shoulders 110 and when the sub of the next lower length is held by a holding wrench 152, the joint between the lengths may be broken. The holding wrench is mounted on the base plate and has three jaws 158 (Fig. 10) pivoted on pins 160. A control ring 164 connected to the jaws 158 by links 170 is rotated by linear motors 176 to close the jaws on the flats 112 of a sub. In the closed position the links transfer the loads on the jaws to blocks 174 supporting the control ring. When the string is being withdrawn from the borehole it is raised by the head and the holding wrench is engaged with the flats of the sub of the next to top length. The head is rotated in the direction opposite to the drilling direction to loosen either the joint between head and string or the joint between the two top lengths. If the joint at the head is loosened the breakout wrench is engaged with the upper sub and the head is rotated to remove the upper section. The head is lowered and engaged with the sub held by the holding wrench, the holding wrench is disengaged and the string is raised so the removal cycle can be repeated. If the joint adjacent the holding wrench is first loosened, the holding wrench is disengaged, the string is lowered, and the holding wrench is engaged with the upper sub and the head is rotated to loosen the joint at the head. The string is raised, the holding wrench is engaged with the second sub and the upper length is removed so that the operations for removing a length may be repeated. The linear motor 76 is supplied with sufficient pressure to bias the head upwardly and so avoid thread damage during breakage of the joint.