EP0015137B1

EP0015137B1 - Apparatus for directional drilling

Info

Publication number: EP0015137B1
Application number: EP80300476A
Authority: EP
Inventors: Pramod C. Thakur; Stephen D. Lauer; Nathandale Farris
Original assignee: Conoco Inc
Current assignee: ConocoPhillips Co
Priority date: 1979-02-21
Filing date: 1980-02-19
Publication date: 1984-02-22
Also published as: PL124814B1; CA1122965A; PL222161A1; DE3066665D1; AU536113B2; ZA797051B; EP0015137A1; AU5418479A

Description

This invention relates to an apparatus for drilling generally horizontal bore-holes in a subterranean earth formation, and more particularly to an apparatus for adjusting the trajectory of such a borehole to maintain same within the upper and lower boundaries of a mineral bed such as a seam of coal.
The drilling of long generally horizontal gas drainage holes in coal beds is known in the art as a method for degasifying a coal bed in advance of mining. The gas drainage holes drilled in this manner are either vented or connected to a vacuum source to remove methane from a coal bed. The greatest problem encountered in drilling these gas relief holes is that of maintaining the bit trajectory within the coal seam such that the resulting holes are actually through the coal seam rather than through an overlying or underlying formation. Control of boreholes trajectory is also important in exploratory drilling for coal or other minerals.
A directional drilling system including a drill shaft, a down-hole fluid motor connected to a rotatable bit, and a deflection means is described in U.S. Patent No. 3,260,318. The deflection means described there is a shaft housing having a slight angle formed therein to divert the drill bit from the axis of the drill shaft. Rotation of the drill shaft and housing through part of a turn changes the direction of the borehole relative to the drill shaft. However this apparatus has been found to give poor results in controlling the trajectory of generally horizontal boreholes. An apparatus for drilling boreholes is disclosed in U.S. Patent No. 3,888,319 wherein a deflection means for drilling apparatus includes a deflection member which is urged by means of hydraulic pressure against a wall of the borehole. However such an arrangement is somewhat awkward mechanically.
According to the invention there is provided drilling apparatus as disclosed in US-A-3,888,319, comprising a down-hole motor, a rotatable shaft for connecting said motor to a drill bit, a non-rotating housing extending from said motor over said shaft, and a deflection member carried by said housing, said deflection member extending radially beyond said housing sufficiently to apply a deflection force to the wall of a borehole during drilling and being movable perpendicularly to the longitudinal axis of the housing, and is characterised in that the deflection force is provided solely by spring means acting between part of the housing and the deflection member, the deflection member being mounted on said housing in a manner to assure rotation of said deflection member corresponding to rotation of said housing and that said spring means continuously urge a borehole wall contacting surface of the deflection member away from one side of the housing and into engagement with the borehole wall with sufficient force to deflect the trajectory of the borehole during drilling.
In operation the deflection member applies a predetermined radial force to a drill bit, causing the trajectory of the borehole being drilled to be deflected in the direction of the applied force.
Further embodiments of the deflection member and the spring means are indicated in claims 2-5.
An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:-

Figure 1 is an illustration of a drilling apparatus showing the relation of a deflection member of the invention to the other parts of the apparatus;
Figure 2 is an exploded view showing the structural details of a preferred embodiment of the deflection member;
Figure 3 is an axial cross-sectional view of the apparatus in the region of the deflection member; and
Figure 4 is a transverse cross-section taken along the line 4-4 of Figure 3.

The relationship of a deflection member of this invention to the other parts of a drilling apparatus is shown generally in Figure 1.
Figure 1 shows a drill shaft 10 connected to an orienting sub 11 and a down-hole motor 12. Motor 12 is preferably a Moyno type fluid motor having a rotatable shaft (not shown) extending through a shaft housing 14 and connected to drill bit 13. Shaft housing 14 extends between motor 12 and bit 13. A deflection member 1 is mounted over a section of shaft housing 14, and extends radially beyond shaft housing 14 at one side. The portion of the deflection member extending beyond the shaft housing includes a wall contacting surface 26 which contacts the wall of borehole 16 being drilled through a mineral bed.
The drilling apparatus including the drill shaft orienting sub, motor, shaft housing and drill bit is preferably of the type generally described in U.S. Patent No. 3,260,318. This type of drilling apparatus, without the deflection member of this invention, has been widely used in the drilling industry.
The details of the preferred version of the deflection member of this invention are shown in Figures 2, 3 and 4.
Shaft housing 14 is machined to provide a reduced section including a top surface 17, sides 18 and 19, and bottom surface 20. Shaft housing 14 includes an internal bore 29 through which a rotatable shaft (not shown) connecting the fluid motor and the rotating drill bit extends. The main body element 21 of deflection member 15 is formed to fit closely over sides 18 and 19 of the reduced section of shaft housing 14 and to be slidable with respect thereto. Recesses 22 and 23 in main body element 21 are provided for containing springs 24 and 25 which urge borehole wall-contacting surface 26 of deflection member 15 radially outward from shaft housing 14. Bottom body element 27 attaches to main body element 21 with fasteners 28 to encompass the reduced section of shaft housing 14 and to compress springs 24 and 25. The deflection force provided by the springs depends to some extent on the particular drilling apparatus and the rate of direction change desired. When the borehole has a diameter of from 75 to 150 mm (preferably 75 to 100 mm) a deflection force of at least 225 newtons is preferred. In order to provide the preferred rate of angle build of about 0.5°/3 m in a coal seam, a deflection force of 450 to 900 newtons is generally adequate.
Figures 3 and 4 show the assembled deflection member. When it is assembled and unrestrained, the springs 24 and 25 act to position the deflection member so that the bottom body element 27 abuts the bottom surface 20 of housing 14, and wall contacting surface 26 extends outwardly beyond the shaft housing 14 sufficiently to apply the desired deflection force to the wall of a borehole during drilling.
The apparatus described above is particularly suited for drilling generally horizontal degasification holes in underground coal seams to reduce the methane concentration in a mine working area in advance of mining the seam. To be effective, the degasification holes must be kept within the boundaries of the coal seam. The deflection member, properly used, enables an operator to maintain the borehole between the upper and lower boundaries of the coal seam.
The method of drilling a borehole in a mineral bed using the deflection member of this invention will now be described. The drilling apparatus is set up, and after drilling an initial surface hole a short distance into the seam, the apparatus as shown in Figure 1 is inserted in the borehole and oriented with the wall-contacting surface 26 of the deflection member oriented against either the top or the bottom of the borehole. In order to guide the drill bit successfully and contain it in the mineral bed, it is essential to know the position of the bit in relation to the roof and the floor of the mineral bed and the pitch and roll of the borehole. Borehole survey instruments which provide the required information are available. These instruments may be pumped down the drill shaft to a position near the motor where they are positioned by an orienting sub, and information as to the position of the borehole may be obtained. The survey probe is then removed, and if a change in direction of the borehole is indicated, the drill shaft is rotated through a part of a turn, thereby also rotating the deflection member the same amount, and drilling is resumed. Normally, the deflection member is oriented to provide either an upward or downward force to the drill bit, although in some cases a side force may be indicated. If the borehole is moving upward, and the surveying probe indicates that the borehole is near the top surface of the mineral bed, the drill shaft and deflection member are rotated 180° to provide a downward force to the drill bit. Drilling in resumed until the surveying probe indicates that the borehole is approaching the bottom layer of the mineral bed, at which time the drill shaft and deflection member are again rotated 180°. This procedure is repeated until the borehole extends the desired distance into the mineral bed.
The deflection member in accordance with the invention has proven to be effective in drilling degasification holes in coal seams in advance of mining. Several degasification holes have been drilled through coal beds for distances greater than 300 meters, thereby providing significant reductions in methane concentrations at the time of actual mining of the coal bed.

Claims

1. Drilling apparatus comprising a down-hole motor (12), a rotatable shaft for connecting said motor to a drill bit (13), a non-rotating housing (14) extending from said motor over said shaft, and a deflection member (15) carried by said housing, said deflection member (15) extending radially beyond said housing sufficiently to apply a deflection force to the wall of a borehole during drilling and being movable perpendicularly to the longitudinal axis of the housing, characterised in that the deflection force is provided solely by spring means (24, 25) acting between part of the housing (14) and the deflection member 15, the deflection member (15) being mounted on said housing (14) in a manner to assure rotation of said deflection member corresponding to rotation of said housing and that said spring means (24, 25) continuously urge a borehole wall contacting surface (26) of the deflection member (15) away from one side of the housing (14) and into engagement with the borehole wall with sufficient force to deflect the trajectory of the borehole during drilling.

2. Apparatus as claimed in claim 1, characterised in that the deflection member (15) comprises a main body element (21) adapted for sliding movement over side surfaces of the housing, the borehole wall contacting surface being formed at the top of said body element and the body element including recesses (22, 23) containing the spring means (24, 25), there being a bottom body element (27) attached to the body element (21) adapted to abut the bottom of the housing when the deflection member is in its uppermost position relative to the housing (14).

3. Apparatus as claimed in claims 1 or 2, characterised in that the spring means comprise a pair of coil springs (24, 25).

4. Apparatus as claimed in claim 3, characterised in that the pair of coil springs (24, 25) provide a deflection force at at least 225 newtons.

5. Apparatus as claimed in claim 4, characterised in that the deflection force is from 450 to 900 newtons.