GB2136852A - Drill rod stabilizing apparatus - Google Patents

Abstract

A drill rod stabilizing apparatus includes a housing 10 adapted to form part of the drill rod string (not shown) and having slidably mounted therein a piston 11 having cam surfaces 15 which bear against borehole wall engaging members 19. Movement of the piston 11 axially within the housing 10 by differential pressure of fluid flowing through a passage 12 in the piston 11 moves the wall engaging members 19 radially and this controls the effective diameter of the stabilizing apparatus. <IMAGE>

Description

SPECIFICATION Drill rod stabilizing apparatus This invention relates to drilling of boreholes through subterranean formations, and more particularly to directional control during substantially horizontal drilling through such formations.

The drilling of horizontal boreholes through coal seams in advance of mining for release of methane gas has recently been a subject of intense interest and activity. It is important in such drilling to be able to control the borehole trajectory so that it remains in the coal seam.

In an effort to provide this control, considerable work has been done in the area of stabilizers attached to a drill rod string. One such stabilizer is described in U.S. Patent No.

4,108,256, and a discussion of related work with stabilizers also appears in that patent.

Expandible borehole wall engaging means on a drill rod string are described in U.S.

Patent No. 3,797,489, but are intended for use in advancing the drill string rather than to provide dierectional control.

There has been a need for a drill rod stabilizer that can provide elevational control to a horizontal borehole being drilled, without the requirement of removing or relocating the stabilizer when a change in borehole trajectory is desired. Such a device provided by the present invention.

According to the invention there is provided a drill rod stabilizing apparatus comprising a housing adapted for series connection with a drill rod string, the housing having a piston slidably mounted therein including cam surfaces which co-operates with cam foilowers associated with a plurality of borehole wall engaging members of the apparatus, the arrangement being such that in use the piston is axially movable within the housing in response ta an increase in upstream fluid pressure from a first position wherein the borehole wall engaging members are retracted to a second, operative position wherein the members extend radiaily beyond the housing.

Thus, apparatus in accordance with the invention has a variable effective diameter and thus enables elevational control of for example a generally horizontal borehole being drilled through a subterranean formation. In a preferred embodiment the stabilizing apparatus piston has tapered outer surfaces which cam against the wall engaging members and movement of the piston axially within the housing is in response to differential pressure of fluid flowing through a passage in the piston.A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is an exploded view of a stabilizing apparatus in accordance with the invention; Figure 2 is a cross section of the apparatus shown in Fig. 1 in its inoperative condition; Figure 2a is a cross section of the forward part of the apparatus in the operative position; Figure 3 is a cross section taken through the line 3-3 of Fig. 2; Figure 4 is a cross section taken through the line 4-4 in Fig. 2; Figure 5 is a cross section taken through the line 5-5 of Fig. 2; Figure 6 is an illustration of a stabilizing apparatus in accordance with the invention in place on a drill rod string, the apparatus being in the inoperative condition; and Figure 7 is a view of the apparatus in place on a drill rod string, the apparatus being in the expanded position.

The operation of the stabilizing apparatus described herein in a drilling operation will be discussed in the context of drilling a generally horizontal borehole through a coal seam, but it will be appreciated that the apparatus has utility in drilling operations generally.

It is often desirable in degasifying a coal seam to drill a series of gas drainage holes for distances of 300 meters and more into the coal seam. Maintaining the bit on a horizontal trajectory parallel to the bedding planes of the coal bed is difficult. The natural tendency of the bit during horizontal drilling is to arc downward due to the forces of gravity. Other factors such as inclusions in the coal bed may also cause the bit to tend to deviate from the plane of the coal seam.

Heretofore, there were several approaches taken to maintain the bit trajectory along the desired path. The primary factors affecting the borehole trajectory are bit thrust and bit rotational speed. As a general rule, decreased thrust and increased rotational speed tend to cause a downward trajectory, while increased thrust and reduced rotational speed tend to cause an upward trajectory. It is also known that positioning a stabilizer on the drill rod near the drill bit increases the tendency of the bit to move upwardly. Using prior art procedures, it was sometimes necessary, upon encountering a downward dip in a coal bed, to remove the drill string from the hole and remove a stabilizer from adjacent and bit.This procedure is time consuming and costly, and it would be desirable to be able to eliminate the effect of the stabilizer without the necessity of removing the drill string from the hole, particularly after the hole has been drilled a substantial distance into the formation.

Stabilizing apparatus in accordance with the invention preferably forms a part of a drill rod string and is positioned adjacent a drill bit as illustrated in Figs. 6 and 7. The details of the preferred embodiment of the stabilizer itself are shown in Figs. 1 through 5.

As best seen in Figs. 1 and 2, stabilizer 31 comprises an outer housing 10 having an inner piston 11 mounted therein for axial sliding movement. Piston 11 includes an axial fluid flow passage through its length and terminating in outlet 1 3 which preferably is a hole drilled through the piston and intersecting passage 12. Piston 11 includes four enlarged shaped sections 14 including cam surfaces 1 5 mounted axially along piston 11.

Each shaped section 14 has an associated wall engaging member 1 6 shown formed of two sections joined by bolts 1 7 and including cam follower surfaces 1 8. When wall engaging members 16 are assembled surrounding a shaped section 14, as best seen in Fig. 2, it will be apparent that axial movement of piston 11 from right to left in Fig. 2 will result in movement of the outer surface 1 9 of wall engaging member 1 6 from a retracted position as seen in Fig. 2 to an expanded position as seen in Fig. 2a. Simultaneously, each of the wall engaging members will be extended to the expanded position shown in Fig. 2a.

Referring again to Figs. 1 and 2, a coil spring 20 extending from spring retainer 21 bearing against a shoulder formed in housing 10 at one end and against a rear piston surface 22 at the other end provides a bias force to piston 11 tending to maintain the stabilizer in the retracted configuration shown in Fig. 2. The extent of the bias force can be controlled by spring strength and by adjustable spring compression setting means comprising a rear piston 22 which is threaded onto an outer sleeve 23 affixed to piston 11.

Locking pin 24 maintains the position of rear piston 22 on sleeve 23.

Forward travel of piston 11 in housing 10 is limited by front stop member 25 which is bolted to housing 10 as seen in Fig. 2. Front piston member 26 is welded or otherwise attached to piston 11, and upon contact with front stop member 25, forward movement of piston 11 is stopped. Rearward movement of piston 11 is limited by contact of stop bolt 27 against stop member 25. Stop bolt 27 is threaded into the end of piston 11 as best seen in Fig. 1.

Fluid passage 1 2 through piston 11 begins at the right and end of the device as viewed in Fig. 2 and extends axially therethrough to fluid outlet 1 3. The forward end of passage 1 2 is blocked by stop bolt 27 such that all fluid flowing through passage 1 2 exits through outlet 1 3.

Front stop member 25, as best seen in Figs. 1 and 3, includes recessed notches 28 which allow fluid flow from fluid outlet 1 3 through notches 28 and on through the housing 10 and the remaining drill rod string and drill bit. This flow pattern occurs when the piston is in the position shown in Fig. 2.

When it is desired to change the stabilizer to the expanded configuration, fluid pressure upstream from the stabilizer is increased, resulting in an increased pressure drop from fluid flow through passage 1 2 which in turn overcomes the bias effect of spring 20 enabling piston 11 to move from the position shown in Fig. 2 to the position shown in Fig.

2a. In order to assure a positive stroke of piston 11, it will be seen that as fluid outlet 1 3 initially moves, it enters front stop member 25 thereby momentarily stopping flow of fluid through passage 1 2 and causing a large increase in the force acting on rear piston surface 22 whereby piston 11 is swiftly and positively moved to the position shown in Fig.

2a with fluid outlet 1 3 extending beyond front stop member 25 such that fluid flow through the stabilizer is resumed.

The force needed to actuate the stabilizer from a retracted to an expanded configuration is a function of several design variables including the strength and compression on spring 20, the size of fluid passage 1 2 and the angle of the cam surfaces which move the wall engaging members. Additionally, as best seen in Fig. 1. a reduced diameter orifice 29 can be placed in flow passage 1 2 and retained therein by orifice retainer 30 threaded into piston 11.

The operation of the stabilizer in accordance with the invention will now be described with particular reference to Figs. 6 and 7. A stabilizer 31 is attached to a drill rod string 32 having a drill bit 33 at its forward end. As drilling progresses through borehole 34, the pressure of fluid flowing through drill rod string 32 is maintained at a pressure low enough to enable stabilizer 31 to remain in the retracted configuration as shown in Fig. 6.

In this configuration, the drill behaves as if there were no stabilizer, and the natural tendency of the drill under these conditions is to develop a slight downward angle in borehole trajectory. After a period of time, determined by operator experience and/or borehole position measurements obtained by known techniques and apparatus, it is desired to develop a slight upward angle in borehole trajectory.

This can be accomplished utilizing the stabilizer of this invention by increasing the pressure of the fluid flowing through the drill rod string to the point where it overcomes the bias effect of spring 20 and enables the piston 11 to move forward, changing the stabilizer 31 from the retracted configuration shown in Figs. 2 and 6 to the expanded configuration shown in Figs. 2a and 7. In the expanded configuration, which is shown somewhat exaggerated in Fig. 7, the wall engaging members 1 6 extend to provide an effective diameter approximating that of the borehole 34. This has the same effect as having a fixed stabilizer near the drill bit.

However, it avoids the necessity of removing the entire drill rod string and inserting a fixed stabilizer to provide the upward trajectory to the borehole.

Thus, utilizing the stabilizer of this invention, an operator can control the trajectory of a borehole by alternately drilling with the stabilizer in the retracted and expanded configurations.

It will be appreciated that numerous variations from and modifications to the device as illustrated and described could be made without departing from the scope of the invention as defined in the claims. For example, the apparatus as described includes a wall engaging member at each 90 arc about the circumference of the stabilizer. More or fewer wall engaging members appropriately distributed could be utilized.

Claims (10)

1. A drill rod stabilizing apparatus comprising a housing adapted for series connection with a drill rod string, the housing having a piston slidably mounted therein including cam surfaces which co-operate with cam followers associated with a plurality of borehole wall engaging members of the apparatus, the arrangement being such that in use the piston is axially movable within the housing in response to an increase in upstream fluid pressure from a first position wherein the borehole wall engaging members are retracted to a second, operative position wherein the members extend radially beyond the housing.

2. A drill rod stabilizing apparatus as claimed in claim 1 wherein said cam surfaces are formed on a plurality of cam members axially spaced along said piston.

3. A drill rod stabilizing apparatus as claimed in claim 2 wherein four cam members and four associated borehole wall engaging members are provided, said cam members and engaging members being arranged such that in the extended position the engaging members are spaced at 90" intervals around said housing.

4. A drill rod stabilizing apparatus as claimed in claim 1, 2 or 3 wherein said piston has a flow passage therethrough and bias means are provided adapted to restrain movement of said piston within said housing in response to a first pressure drop of fluid flowing through said flow passage and to allow movement of said piston within said housing in response to a second, higher pressure drop of fluid flowing through said passage.

5. A drill rod stabilizing apparatus as claimed in claim 4 wherein said bias means is a coil spring surrounding part of said piston.

6. A drill rod stabilizing apparatus as claimed in claim 5 including adjustable spring compression setting means on said piston.

7. A drill rod stabilizing apparatus as claimed in any of claims 4 to 6 including a removable restricting orifice in said flow passage.

8. A drill rod stabilizing apparatus as claimed in any of claims 4 to 7 wherein a piston stop member is provided at the front of said housing, said stop member including longitudinal flow passages therethrough, and wherein the outlet of the flow passage throgh said piston is upstream of said stop member in the retracted position of the wall engaging members and downstream of said stop member in the operative position-.

9. Drill rod stabilizing apparatus substantially as herein described with reference to the accompanying drawings.

10. Drilling apparatus incorporating a drill rod stabilizing apparatus as claimed in any of the preceding claims.