GB2232177A

GB2232177A - Mule shoe assembly

Info

Publication number: GB2232177A
Application number: GB8912023A
Authority: GB
Inventors: Kevin John Burke; Clive Robert Bavington; Roger Michael Nursaw
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1989-05-25
Filing date: 1989-05-25
Publication date: 1990-12-05
Also published as: GB8912023D0

Abstract

A mule shoe assembly for a drilling arrangement incorporates a shuttle valve (7, 8, 9, 15, 16) adapted to open or close to allow liquid flow dependent upon the position of the assembly within a drill string. In use a piston 15 and seals 20 prevent the flow of fluid past the device to allow a probe to be pumped to the bit end of the drill string 1. When buffer 8 engages stop 6, rod 7 is shifted to move piston 15 to the position shown, uncovering part 17 and allowing the passage of fluid (to drive the drill motor) as shown by arrow 22. <IMAGE>

Description

MULL: SHOE ASSEMBLY This invention relates to a Mule Shoe Assembly in or for use with a drilling arrangement for drilling longholes in a strata.

In modern mining techniques where material is extracted from a seam, the seam is often proved in its quality, up to a 1000 metres ahead of a cutting face by longhole drilling in the seam along its length ahead of the face. A probe is inserted into the hole and ascertains the nature of the strata adjacent to the seam ahead of the face and also determines the direction of the hole and the angle of the drilling head in the hole to enable the drill and the hole to be maintained within the seam.

The information derived by longhole drilling is invaluable in ensuring that any problems, such as, faulting or seam deviation can be anticipated before a face arrives at a position of fault or deviation, and this allows pre-planning of the extraction technique to be applied to be prepared for well in advance.

Although the application of drilling long boreholes is generally applied to inseam surveying, it is not limited in its application to this, and may be also applied to drilling strata through which the borehole passes.

A drilling head is driven by a motor at the end of a drill string and the hollow tubular drill string advances into the borehole as the head cuts. Drilling fluid, such as water, is pumped down the drill string and flushes out drilled material from the drill head.

A probe is advanced behind the drill head and this probe is used at intervals to gather information fran the borehole.

This information includes the position of the borehole, its inclination and roll, and the proximity of the boundary of the adjacent strata. From readings derived from the probe, adjustments can be made to the orientation of the probe, to ensure that it continues within the seam or at a desired direction.

Previously it has been necessary to drill a length of about 1.5 to 3 metres and then insert the probe into the borehole, take a reading, and withdraw the probe. This has been very time consuming and with a new technique using a magazine, for supplying drill rods pre-threaded with a cable, which transmits information fran the probe and as is described in our

cpending application (ref 4956 the probe is able to be left down the hole and to take either continuous readings as it advances or to be stopped at any desired interval and to take a reading. There is consequential saving in time since the probe does not have to be constantly withdrawn and reinserted into the drill string everytime a new length of the drill string is added.

In order to ensure that there is not a build up of pressure behind the probe as the drilling advances, it has been necessary to incorporate a by-pass valve behind the drill head, and between it and the probe to operate on a pressure relief basis and to allow the passage of fluid.

According to one aspect of the present invention there is provided a mule shoe assembley in or for use with a drilling arrangement including a down hole drilling motor and a probe arranged to advance within a drill string in which the probe takes readings of the position and direction of the borehole being formed and is capable of changing its direction by orientation of the drill head, the probe and drill head being associated with a drill string and a drilling fluid being pumped down the drill string to advance the probe therein, wherein the assembly includes a spring loaded shuttle valve and a stop member, the shuttle valve being adapted to move against the stop when the end of the drill is reached to displace the piston to open a water passage through the assembly.

The piston preferably moves within a cylindrical housing contained within the drill string and having a external passage for water there around. The cylinder has a slot or a plurality of slots in its side wall, which in normal use are closed by the said piston, but on operation of the assembly are exposed to allow a passage of water.

Alternatively the outer wall of the assembly may be enlarged beyond the diameter of the drill string so as to enable a passage to be opened external to the assembly within the drill string. The fluid used is preferably water.

In order to assist with the understanding of the invention one construction of a mule shoe assembly in accordance therewith would now be described with reference to the single figure of the accompanying drawing. This drawing is a sectional view through the assembly and shows the end of a drill string (1) which is connected by screwing a tapered male portion (2) into a receiving female portion (3) of an adaptor shown generally at (4). The other end of the adaptor screws into a string end adaptor (5). The string end adaptor has secured to it a stop member (6) which is a rigid member secured to the inner wall of the string end adaptor (5) without blocking entirely the passage of the adaptor.

Within the adpator (4) a central shuttle valve is located. This comprises a needle (7), which is connected at one end to a buffer member (8), through a spring (9). The spring is received in an enlarged recess (10) within a sleeve member (11). The sleeve member (11), known as a 'mule shoe', is slidable over a limited amount within the housing of the adaptor (4) and is constrained in its orientation on rotation by a key (12) and in its limit of movement longitudinally by set screws (13) which are secured in the wall of the housing and project into slots (14) in a key body (24).

As its other end the needle (7) carries a piston (15) which is slidable within a mule shoe adaptor (16) which is in the form of a cylinder having an aperture (17) in its wall. A slotted spacer (18) surrounds the aperture (17). The mule shoe adaptor cylinder (16) has a pair of seals (20) surrounding it and moving with it. These seal the butt against the inner wall of the drill string (1) and in normal use provide an effective fluid seal to prevent fluid passing from the inside of the drill string through to the string end adaptor.

As can be seen the mule shoe adaptor cylinder has limited movement within the housing of the adaptor (4) and this movement is constrained by a disc spring washer assembly (21).

In use with the buffer (8) not engaging with the stop member (6) the spring (9) is fully extended and the needle (7) is in a position such that the piston (15) is in the position shown in dotted lines in the drawing. In this position the aperture (17) is completely closed and no fluid can pass there through. The seal (20) prevents this effectively.

When the pressure within the drill string (1) advances the assembly forward so that the buffer (8) impacts on the stop member (6) the spring (9) is compressed and relatively the piston (15) moves to the position shown in full line in the drawing to open the aperture (17) and to allow a passage through the mule shoe adapter cylinder (16) and the spacer (18) as indicated by the arrows (22).

The aperture remains open all the time drilling is in progress. Otherwise there would be no fluid to drive the down hole motor. The only time the aperture closes, is when the fluid has stopped pumping and the probe retracted with the wireline.

Claims

1. A mule shoe assembly in or for use with a drilling arrangement including a down hole drilling motor and a probe arranged to advance within a drill string in which the probe takes readings of the position and direction of the borehole being formed and is capable of changing its direction by orientation of the drill head, the probe and drill head being associated with a drill string and a drilling fluid being pumped down the drill string to advance the probe therein, wherein the assembly includes a spring loaded shuttle valve and a stop member, the shuttle valve being adapted to move against the stop when the end of the drill is reached to open a passage through the assembly.

2. An assembly according to claim 1 in which the shuttle valve includes a piston moveable within a cylindrical housing adapted for location in a drill string, the housing having an external passage therearound.

3. An assembly according to claim 2 in which the cylinder has at least one slot in its wall capable of being closed or opened by the piston.

4. An assembly according to claim 2 or 3 in which the piston is carried on a spindle having at the other end remote from the piston a buffer member adapted to abut the stop member.

5. An assembly according to claim 4 in which the spindle is provided with a spring adjacent the buffer member, the spring being received within and engageable with a sleeve member.

6. An assembly according to claim 5 in which the sleeve member is moveable to a limited extent

7. A mule shoe assembly substantially as hereinbefore described with reference to the accompanying drawing.