Note: Descriptions are shown in the official language in which they were submitted.
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DOWNHOLE FLOW REVERSAL APPARATUS
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
[0001] The present invention relates to a flow reversal arrangement for a
downhole water pump positioned within a coal bed methane well casing. More
particularly, the present invention relates to a water flow reversing
structure
positioned at a pump flow outlet, along with associated conduits for conveying
the
reversed flow to an elevation within the well casing that is below the
elevation of
the pump.
DESCRIPTION OF THE RELATED ART
[0002] An important source of methane, a major constituent of natural gas,
is subsurface coal seams that contain methane. Coal bed methane is a byproduct
of the decomposition of organic material and is held to coal particulates by
water
that is present within the coal seam. However, in such subsurface coal seams
the
gas is not readily available because it is trapped in the seam by the water.
Thus,
to liberate the gas, wells are sunk and include submersible pumps positioned
within well casings for removing the water from the coal seam to lower the
water
pressure and thereby liberate the gas. The gas passes into the well casing and
pumped to the surface, where it is collected at the surface after water has
been
extracted from the coal seam. Such wells are referred to as coal bed methane
wells.
[0003] The water withdrawn from the coal seams is generally pumped to the
surface by submersible pumps driven by electric motors that receive electrical
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power from the surface by means of an electric cable. The composition of the
water contained in such coal seams can vary, but in general it is of low
quality
because it contains large quantities of dissolved mineral solids, including
dissolved
sodium and bicarbonate. As a result, the water has salinity levels that make
it
unsuitable for plants and for discharge onto soils, although it can be and has
been
used as drinking water for livestock. Consequently, when large volumes of
subsurface water from coal seams are brought to the surface, a disposal
problem
is presented by the excess water that cannot otherwise be effectively and
economically utilized. One way to minimize the disposal problem is to reinject
the
water back into the ground, such as into seams that previously had the methane
gas liberated. Another way is to reinject into the ground at a different
elevation
from that from which the methane is being withdrawn.
[0004] There is therefore a need for a compact and simple flow reversal
arrangement that can be contained within a coal bed methane well casing for
injecting extracted coal bed seam water into lower strata.
SUMMARY OF THE INVENTION
[0005] Briefly stated, in accordance with one aspect of the present
invention, a fluid flow reversal apparatus is provided for subsurface pumping
systems and positioned in a well casing. The apparatus includes a pump having
an inlet and an outlet, wherein flow from the pump outlet issues in an upward
direction toward the surface. Means are provided for driving the pump, and a
flow
reverser is positioned adjacent the pump outlet for redirecting pump outlet
flow
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through an angle of about 1800 relative to the upward direction. Conduit means
are connected with the flow reverser for collecting reversed flow that issues
from
the flow reverser and for conveying the reversed flow in a downward direction
substantially 1800 from the upward direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The structure, operation, and advantages of the present invention
will become further apparent upon consideration of the following description,
taken
in conjunction with the accompanying drawings in which:
[0007] Figure 1 is an elevational view of a longitudinal section through a
typical coal bed methane well casing that includes a submersible pump that
forms
part of a coal bed methane recovery system;.
[0008] Figure 2 is an elevational view of the submersible pump portion of
the system shown in Figure 1, including flow reversing apparatus in accordance
with an embodiment of the present invention;
[0009] Figure 3 is a longitudinal cross-sectional view of an upper flow
reversing head assembly;
[0010] Figure 4 is a cross-sectional view taken along the line 4-4 of Figure
3;
[0011] Figure 5 is a perspective end view of the flow diverter of the upper
portion of the flow reversing head assembly shown in Figures 2 and 3, as
viewed
from the lower end of that assembly;
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[0012] Figure 6 is a perspective view of the lower section of the upper flow
reversing head assembly as viewed from the upper end of that section;
[0013] Figure 7 is an exploded perspective view of the upper flow reversing
head assembly;
[0014] Figure 8 is a longitudinal cross-sectional view of the downstream
collection head for collecting and directing reversed flow; and
[0015] Figure 9 is an exploded perspective view of the components of the
downstream collection head assembly as viewed from the top of that assembly.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] Referring now to the drawings, and particularly to Figure 1 thereof,
there is shown a longitudinal section through a typical coal bed methane well
10.
A borehole 12 extends into the earth through successive formation layers from
the
surface, and a tubular well casing 14 is provided within borehole 12. A
submersible pump 16 and an electric motor 18 are positioned within well casing
14. Pump 16 and motor 18 are in the form of a coaxial cylindrical assembly
that
has a smaller outer diameter that the inner diameter of well casing 14 to
define an
annular flow passageway 20 therebetween.
[0017] The upper end of the pump and motor assembly is connected with a
coaxial upper positioning pipe 22 that extends upwardly to and is secured to a
well
outlet 24. The well outlet includes a support for pipe 22, as well as a
methane gas
takeoff connection 26 that is in communication with annular flow passageway
20.
The pump and motor assembly is positioned adjacent to a coal seam 28 for
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withdrawing water from the seam in order to liberate trapped methane gas that
is
contained within the coal seam. Connected to and extending below the pump and
motor assembly is a water downflow pipe 30 that extends to a lower seam 32
that
is at a lower elevation than coal seam 28. A sealing arrangement 34, which can
be in the form of a mechanical packer, or the like, is positioned between
water
downflow pipe 30 and well casing 14 in order to seal off upper coal seam 28
from
lower seam 32.
[0018] Well casing 14 includes a number of upper openings 36 provided in
the casing wall opposite coal seam 28. Upper openings 36 in well casing 14 can
be a series of circumferentially and axially spaced apertures of any desired
form
and size to allow flow therethrough of a sufficient volume of water from coal
seam
28 into annular flow passageway 20. The upper openings allow water from the
coal seam to enter the annular space above sealing arrangement 34 and between
well casing 14 and the pump and motor assembly, and to be drawn into the inlet
of
pump 16 to be pumped from the level of coal seam 28. Normally, water withdrawn
from coal seam 28 would be pumped to the surface through upper support pipe
22, but with the present invention the coal seam water is, instead, directed
downwardly to lower level seam 32.
[0019] In addition to upper openings 36, well casing 14 also includes a
number of lower openings 38. The lower openings in the well casing are
provided
at a level below sealing arrangement 34, and they can have a similar form and
distribution as upper openings 36, if desired. Lower openings 38 serve to
allow
flow of water that issues from the pump and motor assembly to flow through
water
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downflow pipe 30 into well casing 14 below sealing arrangement 34 and into
lower
seam 32, either to replenish previously-withdrawn water from that seam, or to
add
water to that seam and thereby obviate the need to handle and dispose of
withdrawn water at some point above the surface.
[0020] The pump and motor assembly is shown in enlarged form in Figure
2. As shown, pump 16 is a centrifugal pump, although other pump types that can
be accommodated within the well casing can also be utilized. Pump 16 is driven
by submersible electric motor 18 that receives electrical power through a
power
cable (not shown) that extends from the motor to the well surface to connect
with a
surface source of electrical power. Pump motor 18 is supported at its lower
end in
an annular inner collector head 40 that forms part of a downstream flow
collector
42 with an outer collector conduit 44. The upper end of motor 18 is drivingly
connected with the lower end of the pump at a point adjacent to the pump
intake
46.
[0021] The upper end of pump 16 includes a discharge conduit 48 that
communicates with and is connected to a flow reversing head 50. Flow reversing
head 50 includes an inner flow divider 52 that receives and divides pump
outlet
flow and is of annular form, and an outer flow diverter 54 that is connected
to inner
flow divider 52 for receiving pump outlet flow and for changing the direction
of flow
of the pump discharge. Extending from flow reversing head 50 to downstream
flow collector 42 are a number of parallel, circumferentially disposed, outer
conduits 56 that collectively surround pump 16 and motor 18, and that convey
water discharged by the pump and into flow reversing head 50 in a downward
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direction to downstream flow collector 42. Although described and illustrated
herein as a number of individual outer conduits, a single annular conduit can
instead be utilized, if desired.
[0022] Figure 3 is a longitudinal cross-sectional view of flow reversing head
50, showing flow diverter 54 and flow divider 52, each of which components is
coaxial with the other component. Inner flow divider 52, which is of annular
form,
includes an internally threaded inlet 58 for connection with pump discharge
conduit
48 to receive water flow that issues from pump 16. Inlet 58 communicates with
a
cylindrical flow channel 60 that terminates at a converging section 62 that is
immediately upstream of flow outlet 64. The outlet includes an annular lip 66
that
extends into the interior of flow diverter 54. Additionally, and as shown in
cross
section in Figure 4, positioned outwardly of and substantially parallel to
cylindrical
flow channel 60 are a series of circumferentially spaced, axially disposed
outer
flow passageways 68 that extend from an inwardly-directed annular step 70 to
end
face 72 of flow divider 52. A longitudinally-extending cable groove 74 is
provided
in the outer surface of the flow divider between two of outer flow passageways
68
to accommodate an electrical cable (not shown) for providing electrical power
to
pump motor 18.
[0023] Referring once again to Figure 3, flow diverter 54 is of generally
circular cross-sectional form and includes a lower end 76 of generally annular
form
that defines a circumferential flange that is received on and is in surface-to-
surface
contact with inwardly-directed annular step 70 of flow divider 52. Flow
divider 52
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and flow diverter 54 are joined together by a circumferential weld at the
outer edge
of the circumferential flange-annular step interface.
[0024] Flow diverter 54 includes an inner annular chamber 78 that includes
a centrally-positioned, conical flow splitter 80. The flow splitter extends
into inner
annular chamber 78 and includes a pointed apex 82 that is spaced axially from
flow outlet 64 of flow divider 52 from about 0.1 in. to about 0.4 in. Inner
annular
chamber 78 has an outer wall surface 84 that is of generally cylindrical form
and
that includes a series of circumferentially spaced, axially-extending inner
arcuate
recesses 86 (see Figure 5) that are equal in number to, that are equal in
circumferential spacing to, and that have radii that are substantially equal
to those
of outer flow passageways 68 of flow divider 52. Between conical flow splitter
80
and outer wall surface 84 of inner annular chamber 78 is a chamber annular end
wall surface 88 that is concavely curved and that can have a radius of from
about
0.5 in. to about 2.0 in. End wall surface 88 provides a smooth, uninterrupted
transition between the outer surface of conical flow splitter 80 and the inner
surfaces of arcuate recesses 86. As also shown in Figure 5, the outer surface
of
flow diverter 54 includes a cable groove 90 that is aligned with cable groove
74
provided flow divider 52.
[0025] The interior of flow diverter 54 is clearly shown in the perspective
view of Figure 5, in which the form of inner arcuate collector recesses 86 is
visible.
And when flow reversing head 50 is in assembled form, as shown in Figure 3,
the
circumferentially disposed inner collector recesses 86 in flow diverter 54
each
communicate with a respective one of the circumferentially disposed water
outlet
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flow passageways 68 in flow divider 52, which are also clearly shown in the
;perspective view of flow divider 52 in Figure 6. Further, as shown in the
exploded view of Figure 7, flow diverter 54 and flow divider 52 are
circumferentially
arranged so that the respective electrical cable grooves 74, 90 are aligned
with
each other to allow the electrical cable (not shown) to pass from a source of
electrical power at the well upper surface to pump motor 18.
[0026] Referring now to Figure 8, downstream flow collector 42 includes
inner collector head 40 and outer collector conduit 44. Inner collector head
40 is a
substantially cup-shaped member that includes an inner threaded recess 92 for
receiving an outer threaded pump motor connector for supporting motor 18. A
number of circumferentially spaced, axially-extending flow passageways 94,
corresponding in number and in radial and circumferential position with
respective
outer conduits 56 extending from flow divider 52, are provided in annular
outer wall
96 of inner collector head 40. Flow passageways 94 open into the interior of
outer
collector conduit 44, which, as shown, can be of converging form from the
connection with inner collector head 40 and the flow outlet of outer collector
conduit 44.
[0027] Figure 9 shows an exploded perspective view of downstream flow
collector 42, in which inner threaded recess 92 and the circumferentially-
spaced
flow passageways 94 in inner collector head 40 are clearly visible. Outer
collector
conduit 44 and inner collector head 40 are joined to each other by a
circumferential outer weld (not shown). As earlier noted, and as shown in
Figure
2, outer conduits 56 extend between and interconnect flow reversing head 50
and
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downstream flow collector 42. The number and orientation of outer conduits 56
corresponds with the number and orientation of flow passageways 68, 94 in each
of flow divider 52 and inner collector head 40, respectively.
[0028] In operation, and as viewed in Figures 2 and 3, pump motor 18 is
energized to drive pump 16, which, as shown, can be a centrifugal pump. By
virtue of the sealing arrangement 34, which can be a mechanical packer, and
the
upper casing openings 36, water in upper coal bed seam 28 is drawn from the
seam and into pump 16, which directs the withdrawn water into flow reversing
head 50. In the meantime, methane gas that is liberated as a result of the
withdrawal of the water from upper coal seam 28 enters annular passageway 20
between well casing 14 and the pump/motor assembly, from which the methane
gas is withdrawn at the wellhead at methane gas outlet 26.
[0029] The water that is discharged from pump 16 flows through flow
channel 60 of flow divider 52 and exits through flow outlet 64 and into inner
annular chamber 78 of flow diverter 54. The water flow stream leaving the
outlet
of the pump impinges against conical flow splitter 80, which deflects the flow
stream and directs it radially outwardly over 360 along annular end wall
surface
88 of annular chamber 78 and redirects the flow into the several peripheral
collector recesses 86 of flow diverter 54. The water flow stream thus
undergoes a
180 reversal of flow direction within flow diverter 54, from an upward axial
direction to a downward axial direction, and shifts the flow stream radially
outwardly of the longitudinal axis of flow diverter 54.
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[0030] After entering peripheral collector recesses 86, which divides the
flow into a number of individual flow paths, the water flows enter the several
outer
water flow passageways 68 in flow divider 52. From flow divider 52, the
individual
water flows enter into and flow within each of the several outer conduits 56
to inner
collector head 40 of downstream flow collector 42, from which the several
individual water flows enter outer collector conduit 44, where they rejoin
into a
single flow stream to issue from collector tube flow outlet 98 into water
downflow
tube 30, and then into the lower annular chamber defined between sealing means
34, well casing 14, and the floor of the well. By virtue of the pressure under
which
the water is discharged by pump 16, the water passes through lower casing
openings 38 and into lower seam 32, thereby disposing of the extracted upper
coal
seam water and obviating water disposal problems at the wellhead.
[0031] Although particular embodiments of the present invention have been
illustrated and described, it will be apparent to those skilled in the art
that various
changes and modifications can be made without departing from the spirit of the
present invention. Accordingly, it is intended to encompass within the
appended
claims all such changes and modifications that fall within the scope of the
present
invention.
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