GB2053053A - An over-the-top drilling rig with a combined bitching and coupling unit - Google Patents

Abstract

The unit (10) comprises a housing (11) which is rotatably mounted on a drilling table of the rig so that it can turn about the drilling axis (18) through a limited angular extent determined by a pair of blocks (31) and (32) which are fixed on the drilling table. The housing (11) contains a bifurcated bitching member (19) reciprocable within the housing by fluid pressure operated rams (24) and (25) between operative and inoperative positions. In the inoperative position the drilling pipe (2) is free to rotate and to move up or down, but in the operative position a narrow portion (23) of the bitching fork (19) brackets a pair of diametrically opposite flats (8) on the pipe (2) to bitch the pipe. The fork (19), and with it the housing (11), are rotated with the pipe, until the housing impacts against stop surfaces (31a, 32b), or (32a, 31b). This impact exerts a torque between the pipe (2) and the rig driving unit for coupling or uncoupling. <IMAGE>

Description

SPECIFICATION Improvements relating to over-the-top drilling rigs This invention relates to over-the-top drilling rigs. In such rigs the cutting head of the drill is mounted at the lower end of a drilling pipe which extends downwards through a drilling table into the bore hole and which is rotated about its axis by means of a rotary driving unit which is coupled to the upper end of the drilling pipe and is slidably mounted on a mast.

The drilling pipe comprises a number of hollow drill rods which are screwed together end to end and, as drilling progresses, the length of the pipe is periodically increased by fitting another drill rod to the upper end of the pipe. To do this it is necessary to stop drilling and to withdraw the pipe slightly from the bore hole so that the upper end of the pipe is just above the level of the drilling table. The drilling pipe is then bitched (i.e. it is clamped to hold it in position and to prevent it falling back down the bore hole when the driving unit is disconnected), and the joint between the driving unit and the drilling pipe is broken so that the driving unit can be disconnected and raised from the pipe to allow a new drill rod to be screwed into the upper end of the pipe.Similarly, if the upper drill rod is to be removed, it is necessary to withdraw the drilling pipe so that the joint between the top two drill rods is just above the level of the drilling table. The pipe is then bitched and the joint between the two drill rods broken so that the upper rod can be unscrewed and removed.

In over-the-top drilling rigs which are currently in use the drilling pipes are bitched by means of a pair of semicircular hydraulically operated clamps which are arranged to grip the pipe, or in some cases the drill rods are provided, near the upper end, with a pair of diametrically opposite flat forming overhanging portions by which the pipe can be suspended by bitching means moved into engagement with the flats. In order to break the joint between two drill rods or between the upper drill rod and the driving unit, a separate mechanism is provided for gripping the two members and hydraulically exerting an uncoupling torque between them. This uncoupling mechanism is both bulky and complex.

According to the present invention, the drilling table of an over-the-top drilling rig carries a combined bitching and coupling unit comprising a combined bitching member which is movable between an inoperative position in which the drilling pipe is free to rotate about its axis and an operative position in which the member bitches the drilling pipe and is angularly fixed relative thereto, the bitching member, in its operative position, being free to rotate with the drilling pipe through a limited angular extent determined by a pair of fixed stops.

With this arrangement, when the upper drill rod of the drilling pipe is to be removed, the driving unit is raised to lift the pipe, and the pipe is bitched below the joint between the top two drill rods. The rotary driving unit is then operated to drive the drilling pipe sharply in reverse, the bitched pipe turning until the bitching member, or some other part of the unit which turns with it, impacts against one of the fixed stops. This impact together with the torque exerted on the upper drill rod by the driving unit releases the joint between the two rods, and continued reverse driving un screws the upper drill rod until it is free from the rest of the pipe and can then be unscrewed from the driving unit. If the joint is not broken at the first attempt the process is simply repeated.It is hoped however that in most cases the joint will break first time, and towards this end, preferably the pressure at which the hydraulic driving fluid is supplied to the driving unit when operating in reverse is greater (e.g. one and a half times greater) than when the unit is operated in the forward direction.

When coupling a new drill rod or the driv ing unit to the bitched drilling pipe, the rod (already coupled to the driving unit) or the adaptor of the driving unit is screwed into the upper end of the bitched pipe using the rotary driving unit operating in the forward direction.

When the rod or adaptor is fully screwed in, the driving torque is transmitted to the bitched part of the drilling pipe which is then rotated until the bitching member or other part of the unit comes up against the stop at the other end of the limited angular travel of the bitching member. This impact serves to "lock" the coupling. The driving unit is then stopped while the bitching member is retracted to its inoperative position, and the rig is then again ready for operation.

In a drilling rig in accordance with the present invention, not only is the combined bitching and coupling unit simpler in construction, more compact, and cheaper than the separate mechanisms which are currently in use, the actual operations of coupling and uncoupling a drill rod joint are both simpler and quicker with the combined unit.

Preferably the drilling rig in accordance with the invention is intended to be used with drill rods having a pair of diametrically opposite flats on the side of the rod near its upper end, and the bitching member comprises a fork which is slidable between the operative and inoperative positions and which, in the operative position, is arranged to bracket the flats of a drilling rod so that the fork is angularly fixed relative to the rod and the rod is bitched by means of overhanging portions of the rod above the flats resting on the fork.

Preferably the bitching member is recipro cated between the operative and inoperative positions within a housing which is mounted on the drilling table so that the housing, and with it the bitching member, can turn about the drilling axis, and it is the housing which engages the fixed stops to limit the extent of rotation possible for the bitching member and a bitched drilling pipe. The stops are preferably fixed on the drilling table, and are preferably positioned on opposite sides of the housing.In a preferred embodiment of the invention there are two pair of fixed stops which are positioned on opposite sides of the housing near its forward and rearward ends so that two diagonally opposite stops are engaged simultaneously by the housing to limit rotation in one direction, and the other two diagonally opposite stops are engaged simultaneously by the housing to limit rotation in the opposite direction.

Usually the drilling table of an over-the-top drilling rig carries a split sleeve through which the drilling pipe extends, the sleeve acting as a guide and lateral support for the drilling pipe. The sleeve is supported by means of an annular plate which is fixed to its upper end and which rests on the drilling table around the hole through which the sleeve and drilling pipe project. In this case the bitching member housing may be rotatably mounted on the drilling table by means of a circular recess in the underside of the housing into which the annular plate fits.

Preferably the bitching member is hydraulically or pneumatically driven so that it can be retained by fluid pressure either in the inoperative position or in the operative position as desired.

One example of the combined bitching, coupling and uncoupling unit of an over-thetop drilling rig in accordance with the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a perspective view of part of the drilling rig showing the combined bitching and coupling unit on the drilling table; Figure 2 is an axial section, to a larger scale, through the unit when it is in the bitching position in relation to the drilling pipe, the rotary driving unit of the rig not being shown; and, Figure 3 is a plan view of the unit as shown in Fig. 2.

The over-the-top drilling rig illustrated has a reversible hydraulically driven rotary driving unit 1 which is arranged to drive a drilling pipe 2 which extends vertically downwards through a drilling table 3 into the ground below. The driving unit 1 is coupled to the drilling pipe 2 by means of a driving adaptor 4 which is bolted to the output shaft of the unit 1 and is screwed into the upper end of the pipe 2. The driving unit 1 is mounted on a mast (not shown) so that it is movable up and down over the drilling table 3.

The drilling pipe 2 is guided through the drilling table 3 by a longitudinally split guide sleeve 5 (Fig. 2) which projects through a hole 6 in the drilling table 3 and which is supported in position by means of an annular plate 7 welded to the top of the sleeve 5 and resting on the table 3 around the hole 6. The drilling pipe 2 is formed by one or more tubular drill rods screwed together end to end and each being undercut near its upper end to provide two pairs of diametrically opposite flats 8 below overhanging portions 9 as shown in Fig. 2.

The combined bitching, coupling, and uncoupling unit of the rig is indicated generally at 10, and comprises a housing 11 having a base plate 12, a pair of spaced parallel side walls 1 3 and a cover plate 14. The base and cover plates 1 2 and 14 are provided with openings 1 5 and 1 6 respectively to accommodate the passage of the drilling pipe 2. The housing 11 fits over the annular supporting plate 7 of the guide sleeve 5, the plate 7 being received in a circular recess 1 7 in the underside of the housing base plate 12, and in this way the housing 11 is located on the drilling table 3 so that it is rotatable about the drilling axis 1 8 as defined by the axis of the drilling pipe 2.

Mounted within the housing 11 is a bifurcated member 19, forming a bitching fork, having its two arms 20 and 21 bracketing the drilling pipe 2. The distance between the arms 20 and 21 in a section 22 near the open end of the bitching fork 1 9 is greater than the maximum diameter of the drilling pipe 2, but in a narrower section 23 near the root of the fork the distance between the arms is only just greater than the distance between diametrically opposite flats 8 of the drilling pipe 2.

The bitching fork 1 9 is reciprocable in the housing 11 in a direction parallel to the sidewalls 1 3 under the action of a pair of fluid pressure operated rams 24 and 25 which are mounted in recesses 26 and 27 in the fork 1 9 so that they act between the fork 1 9 and the housing 11. Fluid to the rams 24 and 25 is supplied via lines 28 which pass through holes 29 in the cover 14 of the housing 11.

When the rams 24 and 25 are retracted, the bitching fork 1 9 adopts an inoperative position, illustrated by the chain dotted line 30 in Fig. 3, in which the wider section 22 of the fork brackets the drilling pipe 2. In this position the drilling pipe is able to rotate and move up or down perfectly freely. However, when the drilling pipe 2 is in a position as shown in Fig. 2 and the rams 24 and 25 are operated to advance the bitching fork 19, the fork is able to move into an operative position, as shown in Figs. 2 and 3, in which the narrower section 23 of the fork brackets one of the pairs of opposite flats 8 at the upper end of the pipe 2.In this operative position the drilling pipe 2 is bitched, the arms 20 and 21 serving to support the drilling pipe through the overhanging portions 9 of the pipe, and in addition the fork 1 9 is angularly fixed relative to the drilling pipe 2 so that the complete unit 10 is able to rotate with the pipe 2 about the drilling axis 18.

Rotation of the unit 10 with the drilling pipe 2 in the bitched position is however limited by means of a pair of heavy blocks 31 and 32 which are fixed to the drilling table 3 adjacent the sidewalls 1 3 on opposite sides of the housing 11. Each of the blocks 31, 32 is provided with a pair of flat stop surfaces a and b, and the arrangement is such that, when the unit 10 is turned with the drilling pipe 2 in one direction, the housing 11 simultaneously comes up against the stop surfaces 31 a and 32b, the walls 13 of the housing lying flat against these stop surfaces. Similarly, when the unit 10 turns with the drilling pipe 2 in the opposite direction the housing comes up against the stop surfaces 31 band 32a. As will be seen, in this example the stops 31a, 31b and 32a, 326 permit a maximum angular travel of the unit 10 with the drilling pipe of about 30 degrees.

The use of the unit 10 in coupling and uncoupling a joint in the drilling pipe 2 is as described hereinbefore.

Claims (11)

1. An over-the-top drilling rig in which the drilling table carries a combined bitching and coupling unit comprising a bitching member which is movable between an inoperative position in which, in use, the drilling pipe of the rig is free to rotate about its axis and an operative position in which the member bitches the drilling pipe and is angularly fixed relative thereto, the bitching member, in its operative position, being free to rotate with the drilling pipe through a limited angular extent determined by a pair of fixed stops.

2. A drilling rig according to claim 1, for use with drill rods having a pair of diametrically opposite flats on the side and near the upper end, thereby providing the drill rod with overhanging portions above the flats, the bitching member comprising a fork which is slidable between the operative and inoperative positions and which, in the operative position, is arranged to bracket the flats of a drilling rod so that the fork is angularly fixed relative to the rod and the rod is bitched by means of the overhanging portions resting on the fork.

3. A drilling rig according to claim 1 or claim 2, in which the bitching member is reciprocated between the operative and inoperative positions within a housing which is mounted on the drilling table so that the housing, and with it the bitching member, can turn about the drilling axis. the housing engaging the fixed stops to limit the extent of rotation possible for the bitching member and a drilling pipe bitched thereby.

4. A drilling rig according to claim 3, in which the drilling table carries a sleeve for guiding the drilling pipe, the sleeve being supported by an annular plate which is fixed to its upper end and which rests on the drilling table around the hole through which the sleeve and the drilling pipe project, and the bitching member housing is rotatably mounted on the table by means of a circular recess in the underside of the housing into which the annular plate fits.

5. A drilling rig according to claim 3 or claim 4, in which the stops are fixed on the drilling table and are positioned on opposite sides of the housing.

6. A drilling rig according to claim 5, in which there are two pairs of fixed stops which are positioned on opposite sides of the housing near its forward and rearward ends so that two diagonally opposite stops are engaged simultaneously by the housing to limit rotation in one direction and the other two diagonally opposite stops are engaged simultaneously by the housing to limit rotation in the opposite direction.

7. A drilling rig according to any one of the preceding claims, in which the limited angular extent through which the bitching member is permitted to travel by the fixed stops is substantially 30 .

8. A drilling rig according to any one of the preceding claims, in which the bitching member is hydraulically or pneumatically driven so that it can be retained by fluid pressure either in the inoperative position or in the operative position as desired.

9. A drilling rig according to any one of the preceding claims, in which the rotary driving unit of the rig is hydraulically driven and the pressure at which the hydraulically driving fluid is supplied to the driving unit when the unit is operating in reverse is greater than when the unit is operated in the forward direction.

10. A drilling rig according to claim 9, in which the hydraulic driving fluid pressure when the unit is operated in reverse is one and a half times greater than that when the unit is operated in the forward direction.

11. A drilling rig according to claim 1, substantially as described with reference to the accompanying drawings.