Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
This invention relates to a method and apparatus
for drilling generally horizontal boreholes in a subterranean
earth formation, and more particularly to a method and
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 pr'oblem 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 borehole trajectory is also
important in exploratory drilling for coal or other minerals.
Description of the Prior Art
. .
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 ~.S. Patent No. 3,260,318.
The deflection means described therein 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.
Summary of the 'Invention
According to one aspect of the invention, a deflection
device for a drilling apparatus is provided. The deflection
device 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.
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Accordingly this aspect of the invention consists of a
drilling apparatus comprised of a drill shaft extending to a down-
hole motor at the end of said drill shaft, a drill blt rotatably
connected to said motor by a rotatable shaft, and a non-rotating
housing extending from said motor over said shaft and the improvement
wherein a deflection means is attached to said housing, said deflection
means extending radially beyond said housing at one side thereof.
In particular, the invention provides a deflection device
for use with a directional drilling system including a drill shaft,
a downhole fluid motor connected through a rotatable shaft to a drill
bit, and a housing having top, bottom and side surfaces over the
rotatable shaft, said deflection device comprising:
(a) a main body member adapted for sliding movement over
the side surfaces of said housing, said main body member including
a borehole wall-contacting surface at the top thereof and having
spring-containing recess means formed therein;
(b) a bottom body member attached to said main body member
and adapted to abut the bottom surface of said housing when said
main body member is in its uppermost position relative to said housing;
and
(c) spring means in said recess means, said spring means
adapted to constantly urge said wall-contacting surface away from
said housing with a force sufficient to deflect the trajectory of
a borehole being drilled and being the sole means for moving said
deflection device relative to said housing.
The method of using the deflection device includes period-
ically surveying the borehole being drilled, and adjusting the
orientation of the deflection device to maintain the borehole within
the boundaries of the mineral bed through which the borehole is
being drilled.
Accordingly this aspect of the invention consists of a
method of drilling a horizontal borehole through a subterranean
mineral bed with a drilling apparatus having a drill shaft connected
to a down-hole motor which provides rotation to a drill bit and the
improvement wherein:
(a) a deflection device having an outwardly biased wall
contacting surface is provided on said drilling apparatus between
said motor and drill bit and oriented relative to said borehole;
(b) said borehole is extended for a distance into said
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mineral bed while maintaining the orientation of said deflection
device;
(c) information regarding the trajectory of said borehole
is obtained; and
(d) said deflection devlce is rotated through part of a
turn whereby upon resumption of drilling the trajectory of said
borehole is modified.
Brief Desc iption of the Drawings
Figure l is an illustration of a drilling apparatus
showing the relation of the deflection device of the invention to a
drilling assembly.
Figure 2 is an exploded view showing the structural details
of the preferred embodiment of the deflection device.
Figure 3 is a cross section showing the re]ation of the
deflection device to the drilling apparatus.
Figure 4 is a cross section of the deflection device and
drilling apparatus taken along the line 4-4 of Figure 3.
Description of the Preferred Embodiment
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The relationship of the deflection device of this invention
to a drilling assembly 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
shaft housing 14 and connected to drill bit 13. Shaft housing 14
e~tends between motor 12 and bit 13. A deflection device 15 is
mounted over a section of shaft housing 14, and extends radially
beyond shaft housing 14 at one side. The portion of the deflection
device extending beyond the shaft housing includes . . . . . . . . .
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wall contacting surface 26 which contact~ the wall of
borehole 16 being drilled through a mineral bed.
The drilling assembly including the drill
~haft orienting sub, motor, ~haft 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 de~ice of this
invention, has been widely used in the drilling in-
dustry .
The details of the preferred version of
ths deflection device 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 21 of
deflection device 15 is formed to fit closely over
sides 18 and 19 of the reduced section of shaft
hou3ing 14 and to be slidable with respect thereto.
Reces~es 22 and 23 in main body member 21 are provided
for containing springs 24 and 25 which urge borehole
wall-contacting surface 26 of deflection device 15
radially outward from shaft housing 14~ Bottom body
member 27 attaches to main body member 21 with
fasteners 28 to encompass the reduced section of
shaft housing 14 and to compress ~prings 24 and 25.
The defleation force provided by the springs depends
to some extent on the particular drilling apparatus and
the rate of direction chan~e desired. When the
borehole has a diameter of from 75 to 150 mm (prefer-
ably 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
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i8 generally adequate.
Figures 3 and 4 show the assembled deflection
device. When it is assembled and unrestrained, the
springs 24 and 25 act to position the deflection device
~o that bottom member 27 abutts the bottom surface 20
of housing 14, and wall contacting surface 26 extends
outwardly beyond the shaft housing 14.
The apparatus described above is particu-
larly suited for drilling generally horizontal de-
l~ gasification holes in underground coal seams to re-
duce the methane concentration in a mine working area
in advance of mining the seam. To be effective, the
degaæification holes must be kept within the boun-
dari~s of the coal seam. The deflection device,
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 device of this in-
vention will now be described. The drilling apparatusis ~et up, and after drilling an initial surface hole
a 9hort distance into the seam, the apparatus as shown
in Figure 1 is inserted in the borehole and oriented
with the wall-contacting sur~ace 26 of the deflection
devlce oriented against either the top or the bottom of
the borehole. In order to guide the drill bit succes-
fully and contain it in the mineral bed, it is essen-
tial to know the position of the bit in relation to
- the roof and the floor of the mineral bed and the pitch
3a 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 or~enting sub, and information as to the posi-
tion of the borehole may be obtained. The surYey probei8 then removed, and if a change in direction of the
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borehole is indicated, the drill shaft is rotated
through a part of a turn, thereby also rotating the
de~lection device the same amount, and drilling is re-
sumed. Normally, the deflection device i8 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 device are rotated 180 to provide a
downward force to the drill bit. Drilling is resumed
until the surveying probe indicates that the borehole
is approaching the hottom layer of the mineral bed, at
which time the drill shaft and deflection device are
again rotated 180. ~his procedure i8 repeated until
the borehole extends the desired distance into the
minera~ bed.
The deflection device in accordance with the
invention has proven to be effective in drilling de-
gasification holes in coal seams in advance of mining.
Several degasification holes have been drilled through
coal beds for distances greater than 300 meters, there-
by providing significant reductions in methane concen-
trations at the time of actual mining of the coal bed.
It will be apparent to those skilled in the
art that variations and modifications of the structural
details of the deflection device described herein could
be made without departing from the true scope of the
invention as defined in the appended claims.
