Note: Descriptions are shown in the official language in which they were submitted.
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GAS SEPARATOR
FIELD OF THE INVENTION
This invention relates to a gas separator and in particular to a gas
separator for use as an inline, downhole toot for oil and gas well ciritling
and
servicing.
8ACKGROl1ND OF THE INVENTION
DISCUSS1O4V OF THE PRIOR ART
As described in the Latos et al US Patent No. 6,138,757, there are
occasions in the oil and gas industry when a gas is pumped down a well with a
tiquid, Coiled tubing deployed jetting services are commonly performed in
depleted wells using energized fluids - typically nitrogen and water.
Underbalanced operation with energized fluids reduces the potential for well
damage and helps to transport fluids and cuttings to surface. When nitrogen
and
water are jetted as.a two-phase fluid, the jot expands as it leaves the
nozz{e,
reducing the jet impact pressure. Two-phase flow in the jet nozzle may also be
sQnically choked - limiting the jet discharge velocity and effectiveness.
Moreover, fluid jets dissipate rapidly in the surrounding weltbore fluid. Alt
these
factors combine to reduce the effectiveness of a two-phase jet.
Removal of the gas from the fluid stream would enhance the performance
of jetting for well servicing. A single phase water jet has higher density and
stagnation pressure than a mixed-phase jet and would be more effective than a
two-phase jet. Under conditions found in oil and gas well service operations,
the
gas cut in the fluid discharge from the separator should be less than i vol%
to
ensure effective jetting. .
Shrouding the jets with the separated gas would reduce jet dissipation and
increase the effective range of the jet. Many weli service operations required
that
the jetting tools pass through small diameter tubing and obstructions before
cleaning larger diameter tubing, downhole equipment in side-pocket mandreis or
openhole wel4bores; increased jetting range will increase the effectiveness of
jetting tools compared to single-phase fluid jetting for these applications.
The use of energized fluid with a gas separator will also boost the
differential pressure and hydraulic power of the jet by reducing bottomhole
circulating pressure. Increased pressure and power will allow erosion of
harder
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material such as mineral scale, cement and rock, while increased power wii-
improve erosion rates_
An effective gas separator would maintain high efficiency over a relatively
high range of inlet gas fractions_ In a common applicativn, sufficient
nitrogen is
added to reduce the bottomhole pressure to 50% of hydrostatic. Under these
conditions compressed gas makes up 20 to 60% of the volume fraction of the
flow inside the coil. The volume fraction of gas entering the separator may
vary
substantially during a single run due to changes in pressure and temperature
as
the operating depth of the tool increases.
The Latos et al patent (supra) describes a downhole phase separator for
coiled tubing using a cyclonic separator design. This tool provides less than
5%
gas cut for a supply fluid with 30% to 40% gas rontent. Cyclanic separators
are
used to swirl fluid flow through a set of vanes. This approach generates very
high radial accelerations, which provide the separation forces. In small
diameter
tools, the high flow rate generates high turbulent mixing forces that overcome
the
separation forces and limit separation perforrnance.
Rotary gas separators are commonly used in two-phase producticn to
prevent gas from entering electric submersible pumps. The rotary gas separator
is powered by the pump shaft and spins at 3500 or 1750 rpm depending on the
electric motor and power supply. The system includes an inducer to pressurize
the two-phase flow entering the separator. The flow enters a shrouded vane
section where the flow spins and the water or oil moves to the outside due to
centrifugal forces. The shroud rotates with the vanes reducing turbulence in
the
separator. A crossover manifold at the top directs the fluid flow to the pump
and
the gas flow back into the well annulus. The claimed gas cut is less than 10%
for
a wide range of flow rates and gaslliquid flow ratios,
inline rotary gas separators are also used in pipelines to remove small
volumes of condensate from the gas f4ow. This style of separator uses a stator
to
induce swirling flow inside of a drum which includes rotor vanes in the gas
flow.
The rotor provides power to spin the drurn. This type of separator is designed
to
remove all fluid from the gas stream as opposed to providing a low gas cut in
the
fluid.
Yahiro et al in US Patent No. 4,047,580 disclose a method for shrouding a
submerged jet by introducing compressed air through the outer annular ring of
a
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concentric jet nozzle. The air shroud increased the range of the jet by a
factor of
four, The construction of annular gas nozzles is +r.ompiex, particulariy for
high-
pressure fluid jetting.
GENERAL DESCRIPTION OF THE INVENTION
A need still exists for an infine separator for efficiently separating a gas
from a liquid. An object of the present inventian is to meet this need by
providing
a relatively sirnple, compact separator for removing gas from a gas/liquid
mixture.
Another object of the invention is to provide an apparatus combining a
separator for separating gas from liquid and a jetting to+al for inline,
downhole
operations.
Accordingly, the invention relates to an apparatus for separating a gas
from a liquid under pressure comprising:
a tubular housing having an inlet end and an outlet end;
a stator in said inlet end of the housing for causing swirling of gas-
containing liquid introduced into said inlet end;
a drum rotatably mounteq in said housing downstream of said stator in the
direction of liquid flow between said inlet and outlet ends of the housing;
a rotor in an inlet end of said drum for causing the drum to rotate in the
housing;
an end wall in a downstream end of said drum in the direction of fluid flow
through the housing;
liquid outlet ports in the periphery of said end waii for discharging liquid
from the drum;
a gas outlet port in the centre of said end wall for discharging gas from the
26 drum;
a liquid outlet passage in said housing for receiving liquid from said liquid
outlet port and discharging liquid from said housing;
a gas outlet passage in said housing for receiving gas from said gas outlet
port and discharging gas from said housing; .
a first flow restrtction in said liquid outlet for restrioting liquid flow
during
discharge from the apparatus; and
a second flow restriotion in said gas outlet for restricting gas fiow during
discherge from the apparatus.
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In another embodiment, the invention relates to a method of jetting
comprising the steps of passing a two-phase fluid stream through a jetting
tool,
removing gas from the two-phase fluid stream thereby producing a gas-rich
phase and a liquid phase containing less than 1 vol% gas. In a further
embodiment, the gas-rich phase and the iiquid phase are discharged from the
tool and the gas-rich phase shrouds the discharge of the liquid phase.
In yet another embodiment, the invention relates to a method of pumping a
two phase fluid containing a gas and a liquid into a wellbore and separating
the
gas phase phase frarn the liquid phase whereby the resulting liquid phase
contains less than 1 vol% gas.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described below in greater detail with reference to the
accompanying drawings, wherein:
F'igure 1 is a schematic, longitudinal sectional view of a combination
separator and jetting apparatus in accordance with the present invention;
Figure 2 is a schematic, longitudinal sectional view of a second
embodiment of a combination separatar and jetting tool in accordance with the
present invention;
Figure 3 is a schematic, longitudinal sectional view of a combination
separator and rotary jetting tool in accordance with the invention;
Figure 4 is a schematic, longitudinal sectional view of a second
embodiment of a combination separator and rotary jetting tool in accordance
with
the invention;
Figure 5 is a schematic, longitudinal sectional view of a third embodiment
of a combination separator and rotary jetting tool in accordance with the
invention;
Figure 6 is a schematic, longitudinal sectional view of a fourth embodiment
of the combination separator and rotary jetting tool in acGOrdance with the
present invention;
Figure 7 is a schematic{ longitudinal sectional view of a fifth embodiment
of a combination separator and rotary cutting tool in accordance with the
inventinn;
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Figure 8 is an end view of the separator and cutting tool of Fig. 7;
Figure 9 is an isometric view of a stator used in the tool of Fig. 7; and
Figure 10 is an isometric view of a rotor used in the tool of Fig. 7;
MCRiPTlf7N OF THE PREFERRED EMBODIMENT
Referring tcr Fig. 1, a separator in accordance with the invention includes
an elongated tubular housing I containing a rotatable drum 2_ A gas-containing
liquid is intraduced into the inlet end 3 of the housing I via a narrow
diameter
thmat 4. The liquid passes around the conical end 5 of a stator 6, which is
fixedly
mounted in the housing. The stator 6 includes vanes 7 connected to the housing
1 for causing the fluid entering the housing I to swirl. The swirling flow
causes a
rotor 9 to spin_ The rotor 9, which is connected to the drum 2, includes
straight
vanes 10 extending parallel to the longitudinal axis of the drum to ensure
that the
tangential flow of fluid in the drum 2 is small. The rotor 9 is rotatably
supported in
the stator 6 by a bearing 12. The flow of fluid through the rotor 9 causes
rotation
of both the rotor and the drum 2.
An end wall 25 of the drum 2 is rotatably connected to a discharge end of
the housing 1 by a bearing 14 wtiich has a restriction. The bearings 12 and 14
are formed of low friction materials and have a small diameter to limit
bearing
torque. The bearing 14 is a combined }ournal and thrust bearing, while the
bearing 12 is a plain journal bearing. A clearance seal 15 is provided between
the trailing end of the drum 2 and the trailing end 16 of the housing 1. Gas
in the
liquid entering the drum 1 via the stator 6 and the rotor 9 is separated from
the
mixture flowing past the conical trailing end 18 of the rotor 9 by centripetal
acceleration, which forces the liquid 19 to the outside and the gas 20 to the
center of the drum 2. Since the tangential component of fluid velocity is
small,
the total flow velocity is minimized which minimizes turbulent mixing forces
opposing separation.
Preferably a balance pressure port 21 is provided in the rotor 9 for venting
a balance pressure chamber 22 between the stator and the rotor. Reduced
pressure in the chamber 22 reduces the thrust load imparted by the rotating
drum
2 on the thrust bearing 12. Ports 23 can also be provided in the drum 2 near
the
trailing end thereof. The ports 23 are located in a region of low velocity
liquid
flow, which is at a higher pressure than the high velocity region between the
stator 6 and the rotor 9. The ports 23 result in reverse circulation of fluid
which
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counteracts the leakage of gas through the space between the housing I and the
drum 2.
Liquid 19 is discharged from the drum 2 through ports 24 in the periphery
of the end wall 25 of the drum 2. The ports 24 define sections of an annulus.
The liquid flows through a passage 26 in the trailing end 16 of the housing 1
to a
restriction in the form of a nozzle 28. The gas is discharged through a
r,en#ral,
axially extending siphon tube 30 connected to the trai4ing end wall 25 of the
drum
2, and a passage 31 and an orifice 32 in the trailing end 16 of the housing 1.
Multiple gas outlets can be provided.
The gas orifice at the inlet end of the passage 31 is preferably sized as a
sonic nozzle which will pass the maximum volumetric flow rate of gas
anticipated
in a given operation. The gas ciynamics equations for sizing a gas orifice for
a
given pressure, temperature and flow rate are well known to those skilled in
the
art. The liquid nozzles 28 are sized to provide the maximum hydraulic jetting
power taking into account frictional pressure losses in the coil. If the
liquid flow
rate increases and the gas fraction decreases, the differential pressure and
flow
rate across the liquid jet nozzles and gas orifice increases. Liquid entering
the
gas orifice causes it to choke, which reduces the gas flow capacity. The gas
orifice therefore provides a simple and robust means of limiting liquid loss
from
the gas separator while maintaining pressure and hydraulic power of the liquid
jets as the gas flow rates decrease.
The trailing end of the housing I in the direction of fluid flow is closed by
a
jetting assembly 34, which contains parts of the passages 26 and 31, the
nozzle
28 and the orifices 32. The jetting assembly 34 is representative of a variety
of
more complex tools including rotary jetting tools, drilling motors and other
tools
relying on a restriction to fluid flow.
In a preferred embodiment of the invention, the gas orificc 32 is sized to
be slightly larger than required for the maximum flow rate of gas anticipated
in a
given operation. The gas dynamics equations for sizing a gas orifice for a
given
pressure, temperature and flow rate are well known ta those skilled in the
art.
The liquid nozzles 28 are sized for the pumped fluid flow rate at the desired
jetting pressure, taking into account frictional pressure losses in the cail.
If the
gas fraction decreases, fluid will start to enter the siphon tube 30 and the
orifice
32. The two-phase flow capacity of the gas orifice 32 is much smaller than the
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gas flow capacity. The gas orifice 32 therefore provides a simple and robust
means of limiting liquid loss from the gas separator due to variations in
inlet gas
fraction that may occur during operation. Gas separator bench tests show that
the liquid loss is 0,6 !o or smaller while the inlet gas fraction ranges from
29% to
The embodiment of the invention shown in Fig. 2 is similar to that of Fig. I
except that the rotor g is cylindrical with no conical trailing end, and the,
upstream
end 36 of the drum end wail 25 is conical to accelerate the flow of liquid
into the
outlet ports 24 without introducing sudden changes in flow direction which
could
trigger turbulent remixing of gas and liquid. The axes of the nozzle 28 and
the
orifice 32 intersect outside of the aetting assembly 34 so that a gas shroud
is
formed around the liquid jet. The orifice 32 in the embodiment of Fig. 2 is
restricted rather than bearing 14 as in the embodiment of Fig. 1.
Figure 3 shows an apparatus for applications requiring rotary jetting of
liquid leaving the apparatus. The apparatus of Fig. 3 is similar to that of
Fig. I
except that liquid discharged from the drum 2 via the siphon tube 30 passes
through passages 38 in the trailing end of the housing 1, and central axial
passages 39 and 40 via a brake assembly 42 and a head 43, respectively. The
brake assembly 42, which includes a tube 46 canying the head 43, is rotatably
mounted on bearings 47 in the housing 1. The passage of liquid through the
nozzles 44, which are offset from the longitudinal axis of the head 43, i.e.
inclined
with respect to radii of the head 43, causes the brake assembly 42 and the
head
43 to spin in the housing. The nozzles 44 are located beyond the trailing end
of
the housing 1, so that when deployed in a oil or gas production tube 49, the
fluid
jets will remove scale deposits 50. It will be appreciated that any rotary
motor
with an axial flow passage sufficiently large to accommodate the siphon tube
30
can be used in combination with the separator. For example, the Marvin et al
US
Patent Application 2005/6108541 discloses a reaction turbine jet rotor with a
large diameter, unobstructed axial flow passage.
The siphon tube 30 conveys gas from the drum 2 to a centrai outtet orifice
51 in the head 43. The inlet end of the siphon tube 30 is freely rotatable in
the
end wall 25 of the drum 2. The outlet end of the tube 30 is fixed in the
rotatable
head 43, which rotates at a different speed from the drum 2. Thus, a gas
bubble
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forms at the outlet end of the head 51 and the outlet end of the housing 1, so
that
the liquid jets from the nozzles 44 into gas. .
The apparatus of Fig. 4 is similar to that of Fig. 3 except that gas
discharged through the siphon tube 30 passes through passage 54 and is
discharged via a cylindrical passage 65 bqtween the housing I and the
discharge
end 56 of the head 43. The liquid discharged through the ports 24 in the end
wall
25 of the drum 2 passes through a passage 57 in the trailing end of the
housing 1
into the passages 39 and 40, and through the brake assembly 42 and the head
42 to exit through the nozzle 44.
Referring to Fig. 5, another embodiment of the rotary jetting apparatus
includes all of the elements of the apparatus of Fig. 3, except that the
conical
trailing end 18 of the rotor 9 and the brake assembly 42 have been omitted,
and
the cylindrical end wall 25 of the drum has been replaced with an end wall
having
a conical inlet or upstream end 36.
Moreover, in the apparatus of Fig. 5, the head 43 itself is rotatably
mounted in the traiiing end of the housing 1. Liquid is discharged through
passages 38 and 40, and a plurality of inclined nozzles 44 in the trailing end
of
the head 43. The gas is discharged through the end wall 25 of the drum 2 via
the
siphon tube 30, a passage 58 in the trailing end of the head 43 and inclined
nozzles 59_ The trailing end of the siphon tube 30 includes a restriction 60.
The
axes Qf the nozzles 44 and 59 intersect outside of the head 43 so that the
liquid
jets are shrouded in gas.
The apparatus of Fig_ 6 is used for cutting through a formation 60. The
apparatus is similar to that of Fig. 4, except that the rotor 9 is cylindrical
with no
conical trailing end, the trailing end wall 25 of the drum 2 has a conical
leading
end 35, and the brake assembly 42 is omitted. Liquid is discharged via ports
24
in the drum end wal125, a passage 57 in the trailing end of the housing 1, a
central passage 40 in the head 43 and orifices 44. The gas passage 54 defining
a siphon tube contains a restriction 62.
With reference to Fig. 7, another embodiment of the combination separator
jetting apparatus includes a separator including the housing 1 with internally
threaded inlet and outlet ends 64 and,65, respectively for receiving couplings
67
and 68. A stator 70 is fixedly mounted in the inlet end 64 of the housing 1.
As
best shown in Fig. 9, the stator 70 incltides a cylindrical body 71 with a
generally
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hemisphedcat leading end 72. Arcuate vanes 74 extending outwardly from the
body 71 connect the stator to a sleeve 75, which connects the stator to tho
housing I _
A cyiindrical rotor 77 is rotatably mounted on a bearing 78 on the trailing
end of the stator. The rotor 77 (Fig. 10) includes a cylindrical body 80 with
radially extending vanes 81.
The and wall 25 of the drum 2 is rotatably mounted on a bearing 14 at the
inlet end of a sleeve 83 on the siphon tube 30. The bearing 14 is connected to
the inlet end of the coupling 68 by a sleeve 84. The downstream end of the
coupling 68 is connected to a second housing 85 containing a speed governor
87. The speed governor 87 includes a central, tubular shaft 88, which is
rotatably
mounted on bearings 89 in the coupler 68 and bearings 91 in a coupler 92.
Centralizers 93 in the shaft 88 center the siphon tube 30 in the speed
governor.
Segmented weights 94 around the shaft 88 govern the speed of rotation of the
shaft by sliding outwardly against the housing 85.
A jetting assembly indicated generally at 96 is rotatably supported on the
end of the coupling 92 by bearings 97, 98, 99, 100 and 101. The assembly 96
includes a housing 102 carrying a rotatable head 43. The bearing 97 includes a
mid-face vent 104, which vents to the rotatable head 43 and forms a mechanical
face seal with the bearing 98. The bearing 100 is fixed to the rotatable head
43.
The bearing 100 forms a mechanical face seal with the bearing 101 _ The
diameters of the bearing contact surfaces are sized to minimize the mechanical
contact load on the mechanical face seals while maintaining +sffective sealing
under high pressures.
Liquid discharged.from the drum 2 through the ports 24 in the end wall 25
flows through three jet nozzles 106 (one shQwn) in a cap 107 on the rratating
head 43. Gas discharged from the drum 2 travels through the siphon tube 30
and is discharged through a gas orifice 109 in the end of the siphon tube 30
and
through three discharge ports 110 (one shown) in the cap 107 to form shrouds
around the liquid jets.
9
