Note: Descriptions are shown in the official language in which they were submitted.
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PCT/A x'98/00422
1
AN ERECTABLE ARM ASSEMBLY FOR USE IN BOREHOLES
FIELD OF THE INVENTION
This invention relates to an erectable arm assembly for use in
boreholes, and particularly relates to an assembly which can direct a fluid
cutter
into the borehole wall.
BACKGROUND ART
Whipstocks are well known in the mining and petroleum industries
and are used to change the direction of a drill hole (directional drilling).
Since the
earliest times, boreholes were made to deviate by placing tapered wedges or
'Whipstocks" in the borehole to force the bit sideways into a new direction,
and it
is well known that different bottom-hole assemblies had a tendency either to
increase or decrease the inclination of the hole. No one drilling method is
satisfactory for all radii of curvature. It is therefore customary to
distinguish
among these as long-, medium-, short-, and ultra-short-radius methods. The
invention relates to ultra-short-radius methods which are typically defined to
have
a radius of 2ft. (t).6m) or less.
Directionally drilled wells fall into two main categories. In the first
category, the task is to reach locations that are not accessible through
straight,
vertical holes. The objective is to reach a substantial distance horizontally
away
from the drilling location. The second category consists of wells in which
part of
the welt that lies in a particular oil or gas reservoir is given a particular
orientation
so as to increase productivity. An example of this second category is a
vertically
thin reservoir where a horizontal hole can contact a greater part of the
reservoir
than a vertical one, increasing the drainage contact area. It is this second
category to which the invention primarily relates.
Ultra-short-radius whipstocks have been developed that are
applicable to the second category of directional drilling.
A common feature of existing ultra-short-radius whipstocks is a
requirement to incorporate a device in the bottom-hole assembly that either
pushes the drill string around the ultra-short-radius and into the deposit
which is
to be drilled, or uses a complicated hydraulic piston drive arrangement. Drill
strings for use with these whipstocks are either segmented or coiled tubing.
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More elaborate devices are also known to turn a drill string and/or
cutter into the borehole wall. For instance, U.S. patent 5,197,783 describes a
cavity forming device for use in boreholes and which has an erectable arm
member provided with a fluid cutting jet to cut a large cavity in the
borehole.
U.S. patent 4,497,381 describes a drill string bending assembly
which has an extending arm portion to direct the drill string into the
sidewall.
A disadvantage with existing whipstocks and other similar
assemblies is in correctly determining various parameters in the down hole and
drilling process. For instance it is necessary to determine the distance
travelled
by the fluid cutter, whether the segmented or coiled tubing drill string is
feeding
properly through the bore, when the fluid cutter is properly retracted so that
the
arm member can be retracted, the orientation of the arm member, the degree of
inclination of the arm member, and so on.
The assembly of the invention can be used with a drilling system
that uses a high pressure hose as a flexible hose drill string and a self-
advancing
fluid jet cutting nozzle. Such a nozzle has been described in International
Application No. PCTIAU96/00783.
OBJECT OF THE INVENTION
The present invention is directed to a method for directional drilling
of lateral boreholes from an existing borehole, and to an assembly which can
be
towered down the existing borehole and where the assembly has an arm member
which can be erected to position a cutter and/or drill string into a side wail
of the
borehole.
Optionally, the assembly can cut a slot into the side wall of the
borehole as the arm is erected.
It is an object of the invention to provide a method and assembly
which may overcome the abovementioned disadvantages or provide the
consumer with a useful or commercial choice.
In one form of the invention, there resides,an erectable arm
assembly for use in a borehole, the erectable arm assembly comprising a
main body and an arm member, the arm member movable between a
collapsed position in which the assembly can be removed from the borehofe
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and an erected position, the arm assembly being adapted to house a fluid
drilling assembly comprising a fluid cutting device and a flexible hose drill
string such that during erection the arm member can contain at least part of
the fluid drilling assembly, and when in the erected position the arm member
is able to guide the fluid cutting device towards the borehole wall, the
assembly further including at feast one sensor for monitoring the arm
member or the fluid drilling assembly.
In a second form, the invention resides in a method for forming at
feast one lateral borehole from an existing borehole, the method comprising
lowering an erectable arm assembly into the borehole to a desired position,
the assembly having a main body and an erectable arm member, positioning
a self-advanceable fluid cutting device to be supported by the arm member at
least as the arm member is erected, operating the fluid cutting device to self
advance the fluid cutting device from the arm member and into the side wall
of the borehole to form a lateral bore in a direction dictated by the position
of
the arm member in the borehole.
In a third form, the invention resides in an erectable arm assembly
for use in a borehole, the assembly comprising a main body and an arm
member which can move between a collapsed position where the assembly
can be installed and removed from the borehole, and an erected position
where the arm member can guide a fluid drilling assembly towards the
borehole wall.
In another form, the invention resides in a method for forming at
least one lateral borehole of known distance from an existing borehole,
comprising lowering an assembly in the borehole to a desired position, the
assembly having a main body and an erectable arm member, positioning a self-
advanceable fluid cutting device to be supported by the arm member at least as
the arm member is erected, operating the fluid cutting device to self-advance
the
fluid cutting device from the arm and into the side wall of the borehole to
form a
lateral bore in a direction dictated by the position of the arm member in the
borehole.
It is preferred that the method comprises monitoring the length of
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the lateral bore by at least one sensor on the assembly.
The method can be used to form several lateral bores
approximately in the same plane but in different directions, and this can be
achieved by turning the assembly in the existing borehole before launching the
fluid cutter. The method may also be used to form several lateral bores in
different planes.
The method can include an assembly as described above and
having various sensors as described above.
The method and assembly can be used as a tight radius drilling
system (TRD) by which is meant that the flexible hose drill string can be
turned
through 90 degrees within a short radius, typically less than 300mm.
The method and assembly can be used to drill multiple lateral
boreholes from a single existing borehole in the same horizon andlor at
multiple
horizons, for instance to extract methane from coal seams. The existing
boreholes are typically vertical or near vertical. The lateral boreholes
generally
follow the direction of a coal seam and are typically horizontal. After
completion
of the lateral boreholes, production of gas from the well is started by
lowering the
water level in the existing borehole with a simple foot pump or the like. This
technique is extremely effective in coal seams where the methane desorption
pressure is equal to or less than the hydrostatic head of the ground water
table,
as is the case for the majority of the coal deposits in the world.
The current method and assembly can form horizontal lateral
boreholes in excess of 200 metres almost directly from the existing borehole
well.
In this manner it is possible to drain a relatively large area of coal from a
single
borehole. The borehole may extend to a depth of at least 400 metres and in
some cases may exceed 600 metres.
The tight radius bend helps eliminate a lot of the problems
encountered with dewatering larger radius deviated wells by requiring only a
basic foot pump inserted into the existing borehole to drain all of the
lateral
boreholes branching from that well.
The method and assembiy described above are adapted
particularly but by no means exclusively for use in recovering methane from
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underground deposits such as coal seams. Alternatively, one form of the
invention is a method and assembly for recovering methane from underground
deposits which incorporate the above described method for directional drilling
and the assembly.
Suitably, the main body of the assembly is elongate and has a
prismatic configuration or tubular configuration. The main body may have a
channel like cross section.
The arm member may be pivotally attached to the main body such
that it can move about a pivot axis between its retracted position and its
extended
position. It is preferred that the arm member, in the retracted position, sits
entirely within or substantially entirely within the main body. For instance,
the
main body may have an open front through which the arm member can extend.
Alternatively, the main body may be provided with a recessed portion in which
the arrn member lies when the arm member is in the retracted position.
The arm member may comprise a single member, or a number of
members coupled together. For instance, if the flexible hose drill string,
when
guided through the assembly, requires a larger degree of curvature, the arm
member may be formed from two linked members.
The arm member may comprise a single member, or a number of
separate members which can be hinged together, telescoped together, and the
like.
When the arm member is in the retracted position, it should not
form any hindrance to movement of the assembly in the borehole.
The arm member may be moved between its retracted and
extended position by an actuator. The actuator may be located within the main
body. The actuator may comprise a hydraulic or pneumatic ram, one end of
which is attached relative to the main body, and the other end of which is
attached relative to the arm member.
The arm member may comprise a sliding link arrangement. In this
arrangement the arm member may be hingedly coupled relative to the body. A
link member may be pivotally coupled to the arm member and to a slide. The
slide can move along a track and is coupled to an actuator. The actuator can
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cause the slide to move along its track which in turn can cause the arm member
to move between its retracted and extended positions.
It is preferred that the arm member is configured to allow it to
support a flexible hose drill string. Thus, when the assembly is placed in
position, and the arm member is moved to its extended position, the arm member
can be maintained in its extended position and a flexible hose drill string
can be
passed down the existing borehole through an upper portion of the tubular body
and along the arm member thereby positioning the drill string for lateral
borehole
formation.
To achieve this, the arm member may be tubular in configuration to
allow the flexible hose drill string to pass therethrough. Alternatively,
other
methods of supporting the flexible hose drill string are envisaged such as
struts,
guides, and the like.
In another form of the invention, the assembly houses a self-
advancing fluid cutting device. The fluid powered cutting device may be self-
propelled and may be steerable.
The cutting device may be connected to a flexible hose drill string
in the form of a tube or hose or combination thereof, through which high
pressure
fluid can pass to provide the required propulsion of the cutting device, and
optionally also to provide high pressure fluid to the forward nozzles.
In this form of the invention, the cutting device may be held by the
arm member, and if the arm member is tubular, may be positioned within the arm
member.
Guide members in the form of rollers, pulleys, and the like, can be
positioned within the tubular body and/or on the arm member to guide the tube
or
hose through the assembly as the cutting device moves away from the assembly.
The cutting device, in an embodiment, has a substantially tubular steel body
with
at least one forwardly directing high pressure water jet cutting nozzle, and
at
least one rearwardly facing thrusting jet to propel the device in a forward
direction.
The assembly can be positioned at a desired elevation in the
existing borehole and used to launch the cutting device to cut a series of
lateral
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boreholes. The assembly can be turned in the borehole before the cutting
device is again launched. A clamping means can be provided to clamp the
assembly in the borehole at the desired azimuth. The clamping means may be
provided on the assembly below the arm member and may comprise an
extendible member which can be actuated to clamp the assembly against the
borehole wall or casing.
To facilitate smooth movement of the arm member, at least one
flushing jet may be provided to flush away any cuttings which may settle on
the
assembly and especially around the arm member as the cutting device is
operative.
if the assembly has no self slotting capability, a cavity is required in
the existing borehole to allow the arm member to be erected. Conventional
cavity formers are welt known, but these devices are not generally able to
form
cavities of a precise size and shape. If the assembly is lowered into a cavity
which is too large, and the arm member erected, the free end of the arm member
may be some distance from the cavity wall. If the fluid cutting device is
launched,
it can become jammed between the end of the arm member and the cavity wall,
or can lose its desired orientation.
Therefore a cavity reamer can be provided which can cut cavities
of sufficient accuracy to allow proper working of the assembly. The cavity
reamer
may comprise a rotatable main body which can be lowered down an existing
borehole and a plurality of erectable arm members which can be moved between
a collapsed position substantially in line with the main body, and an
extending
position where the arm members contact the side wall of the borehole, the arm
members being provided with cutting means to cut a cavity in the borehole as
the
reamer is rotated in the borehole, and means to urge the arm members into the
extended position.
In another variation to the invention, the arm member can have
cutting means to cut a slot into the wall of the borehole as the arm member
moves towards its extended position. In this embodiment, the assembly can cut
a
slot as the arm member extends from the main body and therefore the need for a
cavity may be eliminated or an undersized cavity may be used.
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The cutting means may comprise any type of cutting means which
can cut into the side wall of the borehole as the arm member is extended.
Suitably, the cutting means comprises high pressure fluid which may pass
through one or more nozzles.
It is preferred that a number of cutting means are provided and
these may be spaced along the arm member. Suitably, the one or more cutting
means are located on a leading edge of the arm member, that is, the edge or
portion of the arm member that is proximal to the side wall of the borehole
which
is to be cut.
If the cutting means comprises high pressure fluid passing though
nozzles, it is preferred that the nozzles are spaced along the arm member such
that the spacing between a first nozzle and a second nozzle is about that of
the
working distance of the high pressure fluid. That is, if the high pressure
fluid is
able to efficiently cut a certain distance, the second nozzle is preferably
positioned at that distance such that high pressure fluid passing through the
second nozzle extends the cutting distance of the combined working fluids.
A number of sensors and/or instrumentation components can be
included in order to control the drilling system. Excess feed of high pressure
hose from the surface can cause bunching at the assembly entry. A hinge joint
on one of the rollers may have a strain gauge to measure force on the roller.
This gives an indication of tension on the high pressure hose through the
assembly. A position transducer in the hydraulic ram and a tilt transducer in
the
arm member can measure the arm member inclination. A contact or inductive
sensor can be located in the arm member to indicate the positive retraction of
the
drilling assembly from the lateral borehole. Pressure transducers and
temperature gauges may be located in the assembly to measure existing
borehole hydrostatic pressure and temperature. An optical sensor may be
located in the assembly to pick up reflected light from cuttings as they exit
the
lateral boreholes enabling colour change to be assessed. An assessment of the
strata in which drilling is carried out can therefore be made.
More particularly, location of the cutting device in the arm member
can be detected by an electro-magnetic sensor which detects the presence of
the
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steel body of the cutting device. The sensor can be positioned in the arm
member. In addition to, or as an alternative to the above electro-magnetic
sensor, an electric sensor can be provided which detects the steel body of the
cutting device by using the steel body to complete an electric circuit.
Correctly determining that the cutting device is fully within the arm
member is important to prevent jamming of the arm member upon its retraction.
The erection angle of the arm member is important to determine
the launch angle of the cutting device within the arm member. A sensor to
determine the extension of the ram can be used which will determine the
erection
angle of the arm member relative to the main body of the assembly. in addition
thereto, or alternatively thereto, an arm member inclination sensor can be
used.
This sensor can comprise a tilt transducer.
In addition to the degree of extension of the arm member from the
body portion, it is important to determine the azimuth of the assembly to
correctly
position the arm member to enable lateral boreholes to be cut around the
existing
borehole. In one embodiment a compass can be used to determine the azimuth.
With the use of flexible hose as the drill string, there is a tendency
for the hose to coil or buckle in the borehole. Therefore, the length of hose
lowered into the existing borehole is not always a good indication of the
length of
the lateral borehole cut by the fluid cutter. The assembly may therefore
include a
sensor to detect the speed and the direction of hose travel through the
assembly.
The sensor may comprise an encoder wheel in the assembly which is biased
against the hose.
Other sensors may be provided which are not part of the assembly
but which determine various parameters of the flexible hose drill string. For
instance, a surface sensor may be provided to determine the amount of tension
in the hose feeding down the existing borehole, and this sensor can comprise a
load cell. The hose may be wound around a hose drum which may include a
load cell to determine the tension in the hose.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will be described with reference to
the following drawings in which
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Figure 1 is a diagrammatic view showing a vertical borehole and a
coal seam;
Figures 2, 2A and 2B are views of an assembly according to an
embodiment of the invention with the arm member in a retracted position;
Figures 3, 3A and 3B are views of the assembly of Figure 2 with
the arm in an extended position.
Figure 4 is a view of an alternative assembly having a single linked
arm member and without cutters, and in the extended position.
Figure 5 is a view of another assembly in the retracted position,
with fluid cutters, and with no provision for a flexible hose drill string to
pass
through the arm member. (ie a pure cutter).
Figure 6 is a view of the assembly of Figure 5 in the extended
position.
Figure 7 is a view of an assembly according to a further
embodiment of the invention and which contains a number of sensors.
Figure 8 is a close up view of the arm member of figure 7.
BEST MODE
Referring to the figures, and initially to Figure 1, there is shown
diagrammatically an ultra-short-radius drilling method and assembly for
cutting a
substantially horizontal bore 63 into a coal seam 10 from an existing vertical
borehole 11.
Figure 1 shows a vertical bore 11 pre-drilled into the ground and
extending through a coal seam 10.
An assembly 14 is shown in Figure 1 and which is positioned in a
pre-formed slot or cavity 60 in one side of vertical borehole 11.
A self-advancing steerable fluid cutting device 16 has been
positioned substantially horizontally into coal seam 10 by virtue of the
assembly
14.
The self-advancing cutting device 16 has a tubular steel body
about 40 - 80cm long and 5 - 15cm in diameter. The body has a number of
rearwardly facing high pressure retro jet thrusters which propel the cutting
apparatus in a forward direction. The front face of the cutting device is
provided
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11
with one or more high pressure water jet cutters to cut the bore. High
pressure
water is supplied to the cutting device by a surface pump 61 and through a
high
pressure flexible hose 62 which is attached to the rear of cutting device 16.
Hose
62 is flexible and can pass through the assembly 14 as the cutting device
moves
along the bore 63. To retract the cutting device 16 it is dragged back along
bore
63 by winding the flexible hose 62 onto hose winch 18, and until the cutting
device is back in the arm member 22.
The flexible hose drill string 62 which extends to the surface and to
a high pressure pump 61 and hose winch 18. High pressure fluid is passed
through hose 62 to power the forward water jet cutters of the device 16 and
also
the retro-thrusters which propels the device forwardly and against the coal
face
to be cut by the water jets.
The cutting device 16, in the retracted "at home" position, is initially
within erectable arm member 22 which can move from a collapsed position
where it is inside main body 20 of assembly 14 to an erect position as
illustrated
in Figure 1. Of course, the arm member can adopt a partially erect position,
with
the position of the arm member determining the point of entry of the fluid
cutting
device 16 into the cavity side wall.
Cutting device 16 can be lowered down the vertical borehole and
fed into arm member 22 when the arm member is in the collapsed position, or
can be prepositioned in arm member before the assembly is lowered into the
vertical bore. In both instances, the cutting device 16 is in the arm member
as it
is raised.
As the cutting device propels itself from the arm member 22 by
virtue of the retro thrusters on the cutting device, various sensors (better
described with reference to Figure 7) detect that the cutting device has been
released from the arm member 22 and track the distance of travel of the
cutting
device. The sensors also ensure that the cutting device is fully retracted
into arm
member 22 before the assembly is collapsed for withdrawal from the borehole,
or
for repositioning in the cavity to allow a further lateral bore to be cut by
the cutting
device.
Assembly 14 is releasably locked into position by a clamping
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means in the form of a borehole clamp 70. Clamp 70 is positioned on a the
centralising tail piece 64 of assembly 14 and below the cavity 60. The clamp
70
consists of an hydraulically operated ram, a number of link members, and an
expanding mechanism which pushes against the borehole casing thereby
securing the assembly against twisting in the vertical borehole. Hydraulic
power
can comprise pressurised water.
Borehole clamp 70 prevents assembly 14 from undesired twisting
in the vertical bore as the cutting device is in operation. As the cutting
device
leaves arm member 22, the high pressure retro jets thrust against the sides of
the
arm member. Should the assembly twist, the arm member will twist away from
the borehole entrance formed by the cutting device, and this can cause a sharp
bend to form in the high pressure hose which can prevent advancement of the
cutting device.
An instrument housing 19 is provided above arm member 22 to
process the data from the various sensors.
Cavity 60 should be formed with good control of the cavity
diameter to ensure that the end of arm member 22, when erect, is against, or
spaced sufficiently close to the cavity wall, to ensure that the cutting
device 16 in
arm member 22 is launched correctly. For instance, the free gap between the
end of arm member 22 and the cavity side wall should be less that half the
length
of the cutting device.
The assembly of Figure 1 is supported by a tubular steel drill rods
17 which consists of rigid steel rods coupled together as is known in the art.
Alternatively, the assembly can be lowered down by coiled tubing as is also
known in the art. A control umbilical bundle 65 which incorporates cables and
hoses for electric, hydraulic and water control, is strapped to tubular steel
drill
rods 17 and sends sensor information from the sensors and instruments within
instrument housing 19 to the surface computer(s).
The assembly therefore allows accurate tracking of the position of
the fluid cutter relative to the assembly.
A surface skid 9 can be provided to contain the necessary
equipment to lower and raise the assembly and to control the cutting device
16,
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and the skid can contain the computers to decode the sensor readings.
Figure 1 is merely illustrative of the general parts and features of
the invention.
Figures 7 and 8 illustrate an assembly 80 provided with various
sensors and instrument packages. Like numbers have been used to identify like
parts. Assembly 80 has an arm member 22 in which a cutting device 16 is
located when the cutting device is in the retracted position. In this
embodiment,
arm member 22 is substantially enclosed to define a cage. Inside the arm
member is an electro-magnetic sensor 81 which detects the presence of the
steel
bodied cutting device 16 using an alternating magnetic field. Sensor 81 is
used
to detect when the cutting device 16 is fully retracted into the arm of the
assembly. It should be realised that failure to fully retract cutting device
16
before collapsing assembly 80 can result to jamming the assembly in the
vertical
borehole. Sensor 81 is positioned such that it detects the steel body of
cutting
device 16 only when the cutting device is fully retracted into arm member 22.
As a backup, a second electric sensor 82 is provided. This sensor
is also positioned on arm member 22 and detects full retraction of cutting
device
16 into the arm member by using the steel body of the cutting device to
complete
an electric circuit which in turn causes the resistivity of the circuit to
drop
significantly when the cutting device makes contact with the sensor.
Assembly 80 has an hydraulic ram 84 which extends and collapses
arm member 22. A ram position sensor 83 comprising a linear transducer is
incorporated into the ram rod. The signal from the transducer relates directly
to
the extension of the ram which can be related back to the angle of elevation
of
arm member 22.
As a backup to the ram position sensor 83, an arm inclination
sensor 85 is provided on arrn member 22. Sensor 85 is a tilt transducer
whereby
electrical resistance can be related directly to the relative orientation of
the
transducer around its central axis. Sensor 85 in combination with ram position
sensor 83 allows for a redundancy in determining the arm inclination, and in
the
event of mechanical failure of arm member 22, the sensors in combination will
provide some diagnostic information.
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14
Assembly 80 further includes a compass 86. Compass 86 is a flux-
gate magnetic compass which is used to indicate the azimuth of the front of
assembly 80. Sensor 86 is electronic and is mounted at the toe of the assembly
away from magnetic material. Sensor 86 is necessary for correctly positioning
the radial Eateral boreholes around the central existing borehole. Sensor 86
will
work in combination with fibreglass casing, as steel casing will cause false
readings. A gyroscopic compass will be used in applications with steel casing.
Assembly 80 further includes a flexible hose travel sensor 87.
Sensor 87 includes an encoder wheel which is used to detect the speed and
direction of hose travel through assembly 80. In the embodiment, sensor 87 is
a
roller wheel which is spring loaded against the flexible hose. As the hose
moves
through the assembly, the roller wheel rotates. A series of magnets are placed
circumferentially around both sides of the roller. Additional sensors are
situated
such that the magnets pass these sensors as the roller turns. A signal from
the
additional sensors can be interpreted for speed and direction of travel of the
hose. The hose travel sensor 87 gives a good indication of whether the cutting
device 16 is penetrating into the coal seam and helps prevent feeding too much
hose from the surface hose winch 18. (Too high a feed rate can cause bunching
of the hose and risk hose damage and jamming of the assembly in the existing
borehole).
Instrument housing 19 includes circuit boards, provides a power
supply to the various sensors, receives signals from the sensors and sends
data
to the surface. Instruments housing 19 contains a temperature transducer 88 to
monitor the temperature inside instrument housing 19. A pressure gauge 90 is
provided to measure hydrostatic pressure.
On the surface, other sensors can be used to determine the
amount of tension in the hose feeding down the existing borehoie. For
instance,
load cells may be positioned on winch drums and supporting structures to
record
loads indicative of hose tension, to ensure that the hose is not
overtensioned.
An additional related sensor can be provided on the hose winch drum and can
consist of a load cell which indicates the torque provided by the hose drum
motor. This data helps determine the tension in the hose at the surface and it
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compliments the load cell situated in the foot of the goose neck.
A surface computer can be used to interpret the signals coming
from the instrumentation on the assembly and at various places around the
surface skid.
Referring now to Figures 2 and 3, there is illustrated in greater
detail the assembly 14.
Assembly 14 comprises a prismatic main body 20 which is
elongate and hollow throughout its length. Body 20 is half hexagonal and open
at the front in cross- section. Body 20 is sized to allow it to be lowered
down
borehole 11 to a desired position, for instance, adjacent a coat seam.
Body 20 is fully open at the front, except for some structural
stiffening members 21. This opening allows an internal arm member 22 to
extend from body 20. Arm member 22 in Figure 2 is positioned entirely within
body 20 thereby allowing the assembly 14 to easily move along bore 11.
Arm member 22, as shown in Figure 2, is formed from two
separate members being a first shorter arm member 23, and a second longer
arm member 22. Arm members 23, 22 are hingedly coupled together at 24 to
form a linked arm member system. The arm members are tubular or channei-
shaped to allow a flexible hose drill string to pass therealong.
The pair of linked arm members 22, 23 provide a larger degree of
curvature to a flexible hose drill string passing down the borehole, into body
20,
along first arm member 23 and along second arm member 22. This provides a
minimum friction path and also reduces the possibility of the flexible hose
drill
string kinking, becoming caught, or being damaged as the flexible hose drill
string passes from a vertical direction to a substantially horizontal
direction.
Guides in the form of rollers and the like 36 are located within arm
members 22, 23 to assist in guiding the flexible hose drill string along the
arm
members.
Arm member 22 is hingedly coupled to one end of an opposed pair
of plate members 27, the plate members being hingedly attached at 28 to body
20, thereby allowing the arm member to move between its extended position and
its retracted position.
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16
In a lower part of prismatic body 20 is an actuator 29 which is in
the form of a fluid ram having a ram body and a ram rod 29A, the ram rod being
able to move into and out of ram body in the usual manner. In figure 3, ram
rod
29A is attached to a slide block 50. Slide block 50 is mounted for sliding
movement within body 20 and can slide between an upper position shown in
Figure 3 and a lower position shown in Figure 2. Slide block 50 is moved
between its upper and lower positions by ram 29. This is better illustrated in
the
embodiment of figure 4.
Hingedly attached to slide block 50 is a link member 51. Link
member 51 is formed from two spaced apart link bars which nest around arm
member 22 when in the retracted position illustrated in Figure 2. This allows
the
assembly to be formed in a compact manner. Link member 51 is pivotally
attached to arm member 22 at a position approximately mid-way along arm
member 22.
Thus, when the ram is operated to extend ram rod 29A, slide block
50 is pushed to its upper position which in turn causes link member 51 to be
pushed out of body 20, which in turn moves arm member 22 to its extended
position illustrated in Figure 3. Retraction of ram rod 29A causes collapse of
arm
member 22 back into body 20. The actuator and link member arrangement
provides a stronger and more robust system.
Arm member 22 in the embodiment is a hollow steel member of
substantially rectangular cross section. On the upper or leading surface 30 is
a
cutting means which comprises pairs, or an array of spaced nozzles 31 - 34.
Nozzles 31 - 34 are attached to a high pressure fluid hose (not
shown) and high pressure cutting fluid can pass through the nozzles to cut a
slot
or cavity in the coal seam.
Nozzles 31 - 34 are spaced from each other by a distance
approximating the working distance of the high pressure fluid passing through
the nozzles. In this manner, efficient cutting of a slot in the coal seam
occurs as
arm member 22 is raised from the inside of main body 20.
Inside arm member 22 are a number of guides in the form of rollers
36. Rollers 36 function to guide the high pressure hose which powers the self-
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17
propelled steerable jet nozzle 16 illustrated in Figure 1. That is, rollers 36
prevent the hose from kinking as the hose passes from the inside of main body
20 to along the inside of arm member 22. Further guides in the form of rollers
37
are positioned inside main body 20 and on a pair of spaced apart plates
between
which the high pressure hose which powers the self-propelled steerable jet
nozzle passes.
In use, assembly 14 is passed down bore 11 until it reaches the
desired position (within a coal seam). Water under high pressure is then
supplied
to nozzles 31 - 34 and at the same time ram 29 is actuated to begin movement
of
arm member 22. Initially, the forward portion of arm member 22 (that is,
adjacent
nozzles 31 ) will contact the side wall of the bore and these nozzles will
begin to
cut into the coal seam. High pressure water passing through nozzles 31 - 34
will
also begin to cut into the coal seam as arm member 22 is further raised. The
amount of movement of arm member 22 can be controlled by the degree of
actuation of ram 29 and thus arm member 22 can be raised to 90~ or over, but
can also be raised partially, for instance, depending on the relative dip of
the coal
seam if the coal seam is not horizontal.
Once the arm member 22 has been raised to its desired amount,
high pressure water is shut off from nozzles 31 - 34 and a flexible hose drill
string
can be lowered down existing borehole 10 and into arm member 22. The end of
the drill string is provided with a cutter, such as a fluid cutter, to then
cut the
passageway into the coal seam.
In a variation, a self-advancing steerable jet nozzle can be pre-
positioned within arm member 22 before the assembly is lowered into the
borehole. In this variation, the high pressure hose which supplies the self-
propelled steerable jet nozzle is guided by rollers 36 and 37 and passes up
bore
11 to the high pressure pump and hose winch 18. Thus, the hose forms the drill
string to the self-propelled steerable jet nozzle.
Water from the high pressure water pump 61 is supplied via the
high pressure hose to the jet nozzle 16 at up to full pressure of 1150 bar at
234
litres per minute, thereby operating the cutting jet or jets and propelling
the
retrojet or jets. The self-advancing nozzle penetrates the coal seam, the
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18
continuous flexible hose drill string (that is, the high pressure hose) is
pulled
behind it.
The self-propelled nozzle can penetrate into the seam for a
distance of up to 200 metres or more with typical drilling times of less than
two
hours. The nozzle can then be retracted by winding the high pressure hose.
Ram 29 can then be actuated to return arm member 22 back into its retracted
position as shown in Figure 2. The assembly 14 can then be pulled up the hole,
or alternatively, can be rotated about its longitudinal axis and the arm
member
extended to cut another passageway into the coal.
The assembly 14 can be attached to the surface by means of a
conventional tubular steel drill rods or some other system such as coiled
tubing.
The tubular steel drill rods or tubing supports the assembly 14 within the
borehole. The drill string or tubing provides the conduit to allow high
pressure
fluid to pass through the drill string or tubing and into cutting nozzles 31 -
34a.
Alternatively, a flexible high pressure hose can be used to supply water to
these
cutters. Rollers 36 - 37 provide a suitable bend radius for the flexible hose
drill
string which is connected to the self-propelled drilling nozzle 16, thereby
allowing
the flexible hose drill string to feed smoothly through the assembly as the
nozzle
penetrates laterally away from the assembly.
Figure 4 illustrates an assembly 40 according to another
embodiment. In this embodiment, the assembly does not have any self slotting
capability, but does house a self-propelled fluid cutting device in the
extendible
arm member. The assembly is lowered down a borehole which has an already
formed cavity in it. Assembly 40 is similar to that described with reference
to
Figures 2 and 3 in that it has an main elongate body 41 which is substantially
hollow throughout its length. In body member 41 is an arm member 42 which
can be moved between a retracted position {not shown) and an extended
position illustrated in Figure 4. In the retracted position, arm member 42 is
entirely within or essentially within body member 41 to allow the assembly 40
to
be lowered into a borehole.
Guides in the form of rollers and the like 46 are located within arm
member 42 and a small mostly internal arm member 43 to assist in guiding the
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flexible hose drill string along main body 40 and along arm member 42 and to
minimise kinking of the drill string.
In a lower part of body member 41 is an actuator 47 which is in the
form of a fluid ram having a ram body 48 and a ram rod 49, ram rod 49 being
able to move into and out of ram body 48 in the usual manner. Ram rod 49 is
attached to a slide block 50. Slide block 50 is mounted for sliding movement
within body member 41 and can slide between an upper position shown in Figure
4 and a lower position (not shown). Slide block 50 is moved between its upper
and lower positions by operation of actuator 47.
Hingedly attached to slide block 50 is a link member 51. Link
member 51 is formed from two spaced apart link bars which can nest around arm
member 42 when arm member 42 is in its retracted position. This allows the
assembly to be formed in a compact manner. Link member 51 is pivotally
attached to arm member 42 at a position approximately mid-way along arm
member 42.
Thus, when the ram is operated to extend ram rod 49, slide block
50 is pushed to its upper position which in turn causes link member 51 to be
pushed out of main body 41 which in turn moves arm member 42 to its extended
position illustrated in Figure 4. Retraction of ram rod 49 causes collapse of
arm
member 42 back into main body 41.
Figures 5 and 6 illustrate an assembly similar to the assembly
illustrated in Figure 4 but now including fluid cutters 52 - 54. These cutters
are
similar to the cutters and arrangement illustrated and described with
reference to
Figures 2 and 3 except that they are rigidly linked to a tramming hydraulic
cylinder {not illustrated). This enables nozzles 52 - 54 to oscillate during
cutting.
In this embodiment, the assembly excludes the provision of a drill string
passing
through the main body and the arm member. This assembly simply creates the
required slots and can then be removed from the borehole after which the
assembly of Figure 4 can be inserted to allow drilling.
An air supply to an air lift device in the foot of the assembly may be
provided to assist in removal of cuttings from the borehole as lateral
penetration
of the drilling nozzle occurs, and as the assembly forms the required slot.
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In one embodiment of the TRD system, a brief description of
operation is as follows -
A borehole which is usually vertical is conventionally drilled from
surface {14'/:' diameter), intersecting the targeted seams for drainage. A
sump
of sufficient capacity to take the cuttings from both the reaming/slotting
operation
and horizontal turnouts, and to house the foot pump once the production phase
of the well commences is included. The well is lined with 95/e" casing. The
casing material over the seam intersections is fibreglass. Alternatively,
other
casing materials such as steel, fibreglass, aluminium or PVC may be used. The
casing is cemented into position. A conventional oilfields hole opener is
lowered
down to the bottom seam intersection and the casing and cement removed. The
hole opener is retrieved and a modified marine casing cutter is lowered down
the
hole and a cavity reamed to a diameter suitable to allow full erection of the
assembly such as over the full interval of the seam. Some coal may be left in
the
roof of the cavity if this improves the stability of the cavity. This
procedure is
repeated for all seams to be drained.
Once the cavities have been formed the TRD skid is moved into
position adjacent to the collar of the well. The assembly is attached to 23/a"
EUE
tubing and the flexible hose drill string is threaded through the assembly
such
that the water jet nozzle is housed in the erectable arm. The control bundle
is
attached to the assembly and a check made on the functionality of the assembly
and its associated instrumentation. The assembly is then lowered down the hole
by means of the tubular steel drill rods. The high pressure hose and control
bundle are fed down at the appropriate speed. The control bundle is strapped
to
the drill rods at regular intervals such that its weight is fully supported.
Centralisers are added every 10m to provide a low friction path for the
passage
of the flexible hose drill string once horizontal drilling commences.
Upon reaching the seam to be drained the assembly is orientated
to the correct azimuth by means of the onboard compass and is clamped against
the borehole wall and the arm is erected. This brings the water jet nozzle in
close proximity to the wall of the cavity. The preferred sequence of
horizontal
drilling is from bottom to top of the existing borehole. Before commencing
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21
drilling, the high pressure pump is brought up to full pressure (e.g. 1150 bar
at
234 litres per minute). The high pressure spinning jets emanating from the
front
of the nozzle commence to create a horizontal borehole. Forward thrust is
generated from the rearward facing high pressure jets. This thrust causes the
drilling assembly to move forward into the cavity wall as high pressure hose
is
fed from the drum on the surface.
In this manner, horizontal boreholes of up to 200 metres in length
are produced. Upon full extension, the pump pressure is dropped to around 700
bar and the drilling assembly retracted back into the erectable arm by means
of
the powered drum mounted on the surface skid. The erectable arm is collapsed,
the assembly unclamped and the assembly rotated to a new azimuth direction.
The assembly arm is again clamped and the assembly arm is erected and
another horizontal hole is drilled. This process is repeated until the
required
number of directional lateral boreholes are formed at each level in each
horizon.
The assembly is then pulled out of the hole. The cuttings formed during the
formation of the lateral boreholes are then cleaned from the sump by means of
a
reverse circulation system.
It can be seen that the assembly, and the combination of the
assembly with a self-advancing steerable drilling assembly within arm member
22 provides a number of distinct advantages over conventional devices. For
instance, the assembly contains an extensive range of instrumentation to
monitor
the borehole conditions and the operation of the lateral borehole formation in
the
self-advancing drilling system. This leads to effective formation of lateral
boreholes to a typical distance of 200 metres and in drilling times of less
than two
hours. The assembly allows rapid repositioning to allow multiple lateral
borehole
creation. This array of multiple lateral boreholes at one or more horizons is
particularly suitable for the extraction of fluids such as water and methane
through a single existing borehole.
The assembly can position the resultant cutting device more
accurately than conventional devices.
It should be appreciated that various other changes and
modifications may be made to the embodiment
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22
described without departing from the spirit and scope of the invention.
